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- Optical Design and Education in Optics
- Poster Session
- Fabrication and Tolerancing
- Illumination System Design
- Other Design Issues
- Testing Based on Imaging
- Optical Testing I
- Interferometry I
- Spectrometry
- Space Optics
- Aspheric Optics
- Infrared Optics
- Display Systems
- Optical Testing II
- Interferometry II
- Profilometry
- Novel Designs
- Integrated Optics
- Poster Session
Optical Design and Education in Optics
Optical instruments and imaging: the use of optics by 15th-century master painters
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We discuss some of the details of the optical technology that was known at the dawn of the Renaissance. We shown that it is quite easy to fabricate concave mirrors of suitable focal length, diameter, and resolution for 15th century artists to have used to project images. The information in this paper complements information on the actual optical evidence that we have presented elsewhere.
Distance-learning postgraduate education in optics and optical design
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Although optics is a common area of activity among professional physicists and engineers, the subject itself is typically not a significant component of Bachelor degrees in physics or engineering. Consequently, large numbers of scientists and engineers find themselves working in the field of optics without formal education in the subject. Although such education would often prove valuable to them, it is not conveniently available via conventional full-time courses. Another group of persons includes those who are not working in an optics-related field, but would like to be, and yet cannot contemplate the cost and dislocation associated with a conventional full-time Masters course. For both these groups, a flexible Masters course in optics by distance-learning could be appropriate. It is for these reasons that interest has arisen recently in such forms of optics education. This paper describes a flexible distance-learning model for postgraduate education in optics that has been implemented at the University of Reading, England, where there has been a full-time optics Masters course in Applied and Modern Optics for almost 40 years. The model is modular and credit-based, and includes various levels of qualification from CPD to Masters. A distance-learning module on optical design is discussed as an example, and it is hoped to make this module freely available on-line via the internet to delegates at this conference for them to explore in their own time. The importance of choosing optical-design case studies appropriate to this learning style is discussed. The problem of lab work within a distance-learning optics course is described, and current and possible future solutions are discussed.
The kurtosis parametric characteristics of light beams passing through aberrated fractional Fourier transforming systems
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Based on the Collins diffraction integral formula and irradiance moment definition, the propagation characteristics of the kurtosis parameter of a Gaussian beam through fractional Fourier transformation (FRFT) systems with spherically aberrated lens are studied in detail. By using the efficient algorithm introduced in this paper, some numerical calculations are done. It is shown that the kurtosis parameter of a Gaussian beam passage through FRFT systems with spherically aberrated lens is very different from that of a Gaussian beam through ideal FRFT systems. What’s more, the effect of different kinds or values of spherical aberration coefficients on the kurtosis parameter is in great difference. The values of the kurtosis parameter of a Gaussian beam through the two types of Lohmann’s systems respectively are no longer equal even in the case of the same fractional orders and the same spherical aberration coefficients. The kurtosis parameter of a Gaussian beam passage through ideal FRFT systems keeps invariable and its value is 3 in the one-dimensional case.
Intensity distribution topography on pupil’s image in EPR
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Eccentric photorefraction (EPR), which is used to determine the refractive error of eye, is greatly relied on the crescent pattern of the pupil image or on the intensity gradient in the principal meridian across the pupil. The vignetting image of the pupil, which is formed by a camera lens aperture with an eccentric light source, and contains a lot of refractive information of the subject eye, has been studied by many authors expecting to get more accurate measurement. In this paper, we have investigated the formation of the crescent image of the pupil. A mathematical expression that calculates the relative intensity in the whole pupil is derived. The intensity distribution is shown in a topography figure that gives a more clear understanding of the pupil image. Based on the discussion of the point light source, light sources are then further extended to other shapes such as line, circle or rectangular form for more general cases, simply by integrating the point source over the scale of the actual geometric form. The analysis and calculation presented are based on Gaussian optics for simplicity. The investigation results show that line source with 0 eccentricity at its one end is suggested in the EPR, in which the intensity slope is much sensitive to the refractive states.
Poster Session
Numerical methods to compute optical errors due to thermo-elastic effects
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A method to compute optical errors subject to temperature variations in the optical components is presented. In general, temperatures, displacements and stresses at arbitrary located FE nodes can not be input directly into optical software. This paper discusses integrated techniques coupling finite element analysis and optical design software. The theory of the method is Zernike polynomials are useful to describe optical surface deformations and wave-front error due to thermal variations and mechanical stress. Thus Zernike polynomials act as the data transmission tool between optical and finite element analysis programs. The coefficient of Zernike polynomials as computed by which we designed codes may be output as CODE V files to evaluate the mechanical effects on the optical performance. An example is demonstrated for thermo-elastic affects the optical performance of a primary mirror of Cassegrain telescope.
Fabrication and Tolerancing
Study on tolerance sensitivity reduction in lens optimization
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A scheme is proposed for the automatic control of tolerance sensitivity during the course of lens optimization. The criteria used in the scheme involve the lens form parameters (S and W) suggested by Sasian and Descour, which quantify the symmetry of the optical system and the optical power distribution among the individual lens elements. It is demonstrated that design results with smaller values of S and W tend to achieve better aberration balance. Thus systems of small S and W values can usually provide good image quality with loose tolerances to manufacturing errors. A test program is developed using the Macro-PLUS language in CODE V. A penalty function is added to the error function for optimization in order to reduce the values of S and W during the automatic design process. Results of manufacturing simulations are given for systems optimized with or without the penalty function, which show that our scheme can successfully reduce the tolerance sensitivity of the design results.
Optical specifications for optical design, testing, and production
W. Andrew Cheng
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We review some of the considerations in establishing optical specifications in taking an optical design through testing and production.
Novel simulation technique for efficient fabrication of 2-m class hexagonal segments for extremely large telescope primary mirrors
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2m class hexagonal primary mirror segments for extremely large telescopes such as OWL and EURO50 receive an increased attention from the optics fabrication community world-wide. We report the development of a novel simulation technique offering cost-effective mass fabrication strategies for such mirrors of tight specifications. A family of static tool influence functions (TIFs) was derived using the Preston’s material removal equation. We then confirmed that the mathematical TIFs can re-produce the material removal foot prints of the bulged precessing tooling reported elsewhere. For fabrication simulation, these TIFs are fed into the in-house developed polishing algorithm that uses a combination of the fixed tool path patterns and the floating trajectory management based on the error grid weighting and the irregular tool paths. The algorithm also optimizes other control parameters including dwell time and tool pressure in real-time as the machine runs. Trial simulation runs using various combinations of the TIFs and the polishing algorithm showed the feasibility of producing the 2m class primary segments with the bulged precessing tooling. The details of the simulation technique together with the results and implications for mass fabrication are presented.
Deformation analysis of a lightweight metal mirror
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The weight of the optical elements of a system used in the aviation and aerospace industry must be as light as possible, on condition that the imaging performance of the system satisfies user’s demand. However, optical elements will deform easily under internal or external pressure if it becomes thinner, and then influences the imaging performance of the whole optical system. In this paper, the main mirror of the Cassegrain system is studied with finite-element analysis (FEA) to predict its surface deformation through simulating its working conditions. The surface deformation is also tested and analyzed after machining and mounting. The obtained interferometric data, Zernike coefficients, is written into CODE V, an excellent software for designing optical systems, to analyze the imaging performance of the designed optical system. Through analyzing the deformation of the metal mirror it can be found that the maxima RMS change of the whole optical system is 0.0059λ, which is only 1.52 percent of the designed value. In the full field of view, the RMS error is less than 0.07λ, that means the imaging performance of the whole optical system is close to the diffraction limit.
Illumination System Design
Noise tolerant illumination optimization applied to display devices
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Display devices have historically been designed through an iterative process using numerous hardware prototypes. This process is effective but the number of iterations is limited by the time and cost to make the prototypes. In recent years, virtual prototyping using illumination software modeling tools has replaced many of the hardware prototypes. Typically, the designer specifies the design parameters, builds the software model, predicts the performance using a Monte Carlo simulation, and uses the performance results to repeat this process until an acceptable design is obtained. What is highly desired, and now possible, is to use illumination optimization to automate the design process. Illumination optimization provides the ability to explore a wider range of design options while also providing improved performance. Since Monte Carlo simulations are often used to calculate the system performance but those predictions have statistical uncertainty, the use of noise tolerant optimization algorithms is important. The use of noise tolerant illumination optimization is demonstrated by considering display device designs that extract light using 2D paint patterns as well as 3D textured surfaces. A hybrid optimization approach that combines a mesh feedback optimization with a classical optimizer is demonstrated. Displays with LED sources and cold cathode fluorescent lamps are considered.
Optical design of free-face reflective headlamps
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Headlamps are installed at the head of automobiles for road lighting. About the illumination and anti-dazzle, some standards such as the standard of ECE are established. Now more and more free face reflective headlamps (FFR headlamps) are applied, and the light distribution design of FFR mirror becomes an important subject in the field of automobile assembling part. In this paper the surface shape of FFR headlamps is analyzed and described as a multi-partition aspherical surface with some simple parameters. According to the fundamental principles of geometrical optics and using the theory of ray transmission with energy, millions of real rays emitted from lower beam filament and high beam filament are traced and the relative intensity of illumination at the test screen with distance of 25m from the automobiles is obtained. In this paper the description of FFR mirrors is discussed, the algorithm of FFR headlamp design is presented, the flow chart is given and the light distribution simulation software with friendly interfaces is developed. In the light distribution graphic interface of the software, the illumination area could be dragged to a certain position while the parameters of current partition at the FFR mirror will be automatically changed. Using this software the FFR headlamps satisfying criteria will be designed very quickly and the 3D coordinates of any points at the mirror will be obtained. This makes CAM of FFR headlamps easy.
Computer-aided design and optimization of free-form reflectors
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The design theory and method for illumination systems with free-form reflectors are studied. Uniform bicubic B-spline surfaces are used to describe the shape of the reflector, and the control point coordinates are calculated by equation solving after the shape points of the reflector are obtained. An iterative method is developed to calculate the coordinates of the intersection point of an incident ray with a B-spline surface in 3D space. Formulae are given to calculate the direction cosines of the surface normal at the intersection point. For segmented reflectors, a method is presented to rapidly determine the segment with which the incident ray strikes, which can greatly improve the efficiency of ray-tracing for segmented reflectors. The damped-least-squares method is used to optimize the B-spline surface reflector. The Z-coordinates of the control points are adjusted through the optimization, so that the light distribution generated by the reflector with a real (extended) source meets the design requirements.
Reflector optimal design for segmented reflector lamp
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This paper analyzes the error types for segmented reflector lamp, and puts out an optimal design method for segmented reflector based on error analysis. The paper establishes optimization model for segmented reflector considering the error analysis in manufacturing process of segmented reflector. Based on this optimization model it could give out shapes of reflector patches for segmented reflector which is low sensitive to the errors, and direct the plan process efficiently and get out the final reflector consistent with the designed one, which is important for auto lamp design.
A novel LED illumination system used in hand-held projector
Wei Lu,
Peifu Gu,
Mo Shen
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Recently high brightness LED developed rapidly and would be a suitable replacement for hand-held projector compared with UHP lamp. Generally, uniformity and low etendue is required in illumination system of projection display, while the emitting distribution of HB-LED always has non-uniformity and large view angle. In this paper, we have designed a preliminary illuminator consisted of two curved reflective fly’s eyes especially for the lighting characteristic of HB-LED. By means of the asymmetric configuration we can get the small exit ray angle which reduces the etendue of illumination system. Because of reflective system, the embodiment is shorter than 20 mm. The uniformity is above 80% and the efficiency of the illuminator is better than 75%.
Rigorous electromagnetic analysis of Talbot effect with the finite-difference time-domain method
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We present the electromagnetic analysis of Talbot effect with the finite-difference time-domain (FDTD) method. To our knowledge, it is the first time that FDTD method is applied to analyze the performance of a Talbot illuminator. Furthermore, self-imaging performances of a grating with different flaws are analyzed. The FDTD method can be applied to analyze this kind of diffraction. Of course it also can be analyzed with the Fourier transform method. But for this non-period grating, it will be more complex. In addition, the grating employed here is a high-density grating. The Fourier transform method is not rigorous enough. For these reasons, the FDTD method can show the exact near-field distribution of different flaws in a high-density grating, which is impossible to attain with the conventional Fourier transform method.
Other Design Issues
Studies on dynamic behavior of rotating mirrors
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A rotating mirror is a kernel unit in a Miller-type high speed camera, which is both as an imaging element in optical path and as an element to implement ultrahigh speed photography. According to Schardin’s Principle, information capacity of an ultrahigh speed camera with rotating mirror depends on primary wavelength of lighting used by the camera and limit linear velocity on edge of the rotating-mirror: the latter is related to material (including specifications in technology), cross-section shape and lateral structure of rotating mirror. In this manuscript dynamic behavior of high strength aluminium alloy rotating mirrors is studied, from which it is preliminarily shown that an aluminium alloy rotating mirror can be absolutely used as replacement for a steel rotating-mirror or a titanium alloy rotating-mirror in framing photographic systems, and it could be also used as a substitute for a beryllium rotating-mirror in streak photographic systems.
Testing Based on Imaging
Eye gazing direction inspection based on image processing technique
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According to the research result in neural biology, human eyes can obtain high resolution only at the center of view of field. In the research of Virtual Reality helmet, we design to detect the gazing direction of human eyes in real time and feed it back to the control system to improve the resolution of the graph at the center of field of view. In the case of current display instruments, this method can both give attention to the view field of virtual scene and resolution, and improve the immersion of virtual system greatly. Therefore, detecting the gazing direction of human eyes rapidly and exactly is the basis of realizing the design scheme of this novel VR helmet. In this paper, the conventional method of gazing direction detection that based on Purklinje spot is introduced firstly. In order to overcome the disadvantage of the method based on Purklinje spot, this paper proposed a method based on image processing to realize the detection and determination of the gazing direction. The locations of pupils and shapes of eye sockets change with the gazing directions. With the aid of these changes, analyzing the images of eyes captured by the cameras, gazing direction of human eyes can be determined finally. In this paper, experiments have been done to validate the efficiency of this method by analyzing the images. The algorithm can carry out the detection of gazing direction base on normal eye image directly, and it eliminates the need of special hardware. Experiment results show that the method is easy to implement and have high precision.
Research on modern testing technique of optical system magnifying ratio based on CCD imaging theory
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The paper discusses a new kind of modern testing method used in magnification of telescopic optical system, which applied the technique of photoelectric imaging creation automatically based on DLP theory and the technique of collecting image based on CCD imaging theory. This method simplifies customary measuring process, realizes objective and automatic measuring, and avoids subjective error which artificial factor leads to with using customary testing method, so as to attaining higher testing precision.
Research on testing technique of image inclining and graduation inclining of optical system based on CCD imaging theory
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This paper brings forward a kind of technique of creating photoelectricity imaging automatically with DLP, the technique of CCD photograph and the modern testing method between the technique of computer imaging disposing and the technique of optics system image and graduation lean. This method can remove a lot of vice, which is tiredness of examining method by eyes, the effect of man-made factors, and so on. So it can make measuring, the degree of automatization more veracity, even realize digitalization.
Design of a synchronized scanning system for size measurement of human body
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In this paper, a structured light system based on synchronous scanning technology is developed for meeting the need of body surface acquisition. The proposed system is composed of a
fixed CCD camera, a fixed structured light projector and a mirror scanner. While the mirror is reflecting light stripes and scene images, the camera acquires a series of body section images from the scanner. After extracting the trace of laser stripes and calculating the relative 3-D coordinate of the illuminated pixels on the series of CCD images, the system can acquire the spatial profile of the
inspected body surface. Moreover, a prototype is developed according to the results from geometrical analysis mentioned above. The experiment data obtained from the scanning system are shown. This synchronized scanning system can be widely applied in the custom design, surgery navigation and the other optical measurement field in the future.
Optical Testing I
Implementation of Hartmann test for measuring 0.9-m aspheric mirror
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Most aspheric mirrors have been measured by null lens test or computer generated hologram method. This approach, however, requires that the surface be close to the target shape; otherwise, the testing may not be possible or correct. Hartmann test has an advantage in that it has larger dynamic range than the general interferometer, which means that the surface can be measured with a Hartmann test from the early stage of polishing process. In this paper, authors show the measurement capability of Hartmann sensor, compared to the ZYGO phase-shifting interferometer and implement the Hartmann test to the measurement of 0.9 m aspheric mirror from the beginning of the polishing process. In order to increase the measurement accuracy and reduce the measurement time, authors develop the special null optics. The early stage of aspheric mirror was measured with the inteferometer and Hartmann sensor together, to show the great usefulness of Hartmann test in the measurement of large wavefront error, which can in turn reduce the manufacturing time of large optics.
An automatic system for measurement of retardation of wave plates based on phase-shifted method
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A practical system is described to measure the retardation of wave plates with phase-shifted method. The tested wave plate is put in and the original angle between the axis of it and the analyzer is random, not 45 degree. For the measurement is made rapidly and automatically, a standard wave plate act as a compensator, the stepping motor is used to drive the analyzer to realize phase shifting and a grating encoder is used to measure its rotating angle. At the same time, while the beam comes out from the analyzer, the photoelectric detector gets its intensity, and then the signals is magnified, filtered and sent to computer through its serial port. The results show the system has the advantages of costing little time and high accuracy.
Method to enhance the accuracy of the retardance measurement of quarter-wave plates
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A novel method used for the enhancement of the accuracy of the measurement of the retardance of a quarter-wave plate employing two polaroids and a prism is reported under the condition of knowing the direction of the fast axis of the plate. The theoretical analysis of the principle and the uncertainty formula are given. An application example is also demonstrated. The measured result of the example is verified with an experiment. The main advantages of this method include the accuracy enhancement, simple measuring setup and easy operation.
Research and development of heterodyne dispersion meter
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A heterodyne dispersion meter based on total-internal reflection effects and common-path configuration is presented. It is used to measuring the dispersion power of an optical material or component for many applications in industries. The phase difference between S and P-polarizations at the total-internal reflection condition can be extracted and measured accurately by using heterodyne interferometry. The constants of dispersion formulas built by traditional ways could be revised by this method. It has some merits, such as, high resolution and stability, easy to operate, and real-time measurement.
Measurement of the linear birefringence inside bulk glass current sensing elements with a retarder
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Linear birefringence inside the sensing head can obviously affect the performances of optical (fiber-optic) current transformers. Therefore, it is important to measure the linear birefringence for the design and the property enhancement of optical current transformers. A method employing a retarder to measure the linear birefringence inside the bulk glass current sensing head is reported. The theoretical analyses of the principle and the measurement uncertainty of the method are given using Jones Matrix as a mathematical tool. An applied example is also given. The main advantage of this method is that it can uniquely determine the value of the linear birefringence inside the sensing head, which overcomes the shortcoming of that only a trigonometric function value of the birefringence can be determined by the method reported before. Furthermore, there are some other advantages such as simple structured, practical and that the devices needed are easy to obtain.
Interferometry I
Improved straightness interferometer for nanometrology
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The interferometers which measure the displacement parallel to the measurement axis are called linear interferometers, while those measure the displacement orthogonal to the measurement axis are called straightness interferometers. Theoretically, the orthogonal characteristic between the displacement and the measurement axis does not introduce optical path difference (OPD) and thus, makes null signal. These lead to the straightness interferometer difficult to be implemented. A generalized laser interferometer system based on three design principles, the heterodyne frequency, the avoiding mixing, and the perfect symmetry, is described. These design principles give rise to the interferometer a highly stable system with no periodic nonlinearity. A novel straightness sensor, consisting of a straightness prism and a straightness reflector, is incorporated into the generalized system to form a straightness interferometer. With the help of a Hewlett-Packard commercial linear interferometer, the validity of the developed straightness interferometer has verified. Based on the present design, the interferometer has a gain of 0.348, a periodic nonlinearity of less than 40 picometers, and a displacement noise of 4 pm/√Hz at bandwidth 7.8 kHz. This system is useful in precision straightness measurement.
A radial-shearing interference system of testing laser-pulse wavefront distortion and the original wavefront reconstructing
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It is an important part to measure the distortion and divergence of laser pulse wavefront in ICF (Inertial Confinement Fusion). The paper described a radial shearing interference system with spatial phase modulation. It can be used for testing the wavefront distortion and control the beam quality. Because it is a cyclical common path interference system and no any reference surface, both radial sheared wavefront are formed by a Galilean optical system. A 512x512 pixels CCD camera recorded interference pattern. The wavefront reconstructed is finished by means of optical information processing method and software. The software procedure consists of the Fourier transform, shifting frequency, inverse Fourier transform, unwrapping 2π and wave iterations reconstructed. The interferometer has been used for testing a wavefront distortion of laser pulse with 1064nm near-infrared wavelength and 10 ns pulse time width. Results of the pulse wavefront quality and distribution of energy can be displayed by a perfect software procedure. Diameter of beam be measured is up to 150 mm. The testing precision of RMS(root-mean-square) is better than 1/15 wavelength.
A multifunctional phase-shifted interferometer with small dimension
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A portable phase-shifted interferometer with multiply usages is described. Several techniques are studied and used in this interferometer. In order to test an optical piece with obscuration or irregular edge, we study the seed-algorithm for wavefront reconstruction. For testing a corner cube reflector (CCR), we investigate the model to calculate its exit wavefront and angle error. To measure the figure of a convex or concave spherical surface, we develop a series of reference transmission spheres.
Research of Doppler velocity interferometer system for laser-driven shock wave
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VISAR is an effective tool to measure very high-speed motion objects. However, because of the limitation of response speed of the detector, it is unable to resolve the number of shifting fringes in
a very short time at the beginning of motion of the object, which lead to a question of fringe lost. The Double-sensitivity VISAR is one of ways to solve the question. In this article, we advance an
improved double-sensitivity VISAR that only uses a set of velocity interferometer and detection system.
Real-time measurement of concentration and temperature of solution by two different wavelengths Mach-Zehnder interferometry during crystal growth
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Real-time measurement of the variation of the concentration and temperature of the solution in liquid-phase by the use of contactless Mach-Zehnder interferometry was presented in this paper. The relationships between the temperature, concentration and refractive index of solution were investigated. The feasibility of the measurement of the temperature and concentration variation separately when they altered simultaneously was discussed. Consider the practical application, Koster prisms were chosen to built the Mach-Zehnder interferometer instead of common mirrors and beamsplitters. The use of Koester prisms made the optical system compact and increased the system stability. Utilizing two wavelength interference measurement we can work out the variation of temperature and concentration from the variation of the refractive index data using fitted second order polynomial was drew. The experiment of measuring the solution concentration and temperature by use of the undersaturation aqueous solution of KDP was done.
Spectrometry
Low polarization sensitivity resolution of the new moderate-resolution imaging spectrometer
Linghua Guo,
Zhaojun Liu,
Jun Gao,
et al.
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Radiation of most target scene has the polarization characteristic. Especially, polarized light, which is from the earth and the atmosphere, of visual band, near infrared band, and short wave infrared band is so strong. The polarization degree of blue band and green band is more than 25%. This new moderate resolution imaging spectrometer is a remote sensor for acquiring dynamic spectral and image data from the surface of land, water and from lower atmosphere. The radiance of target scene detected by the remote sensor is the result of polarization characteristic of the remote sensor and the target scene. So, low polarization sensitivity design is the key technology of such remote sensor. We have applied a high efficient scan subsystem, which is new, light, double-sided, to this instrument. Further more, polarization sensitivity was decrease by the additional polarization compensator, the change of optical axis and etc. The engineering model (EM) was completed. Its performance goal is better than required and for 0.4μm≤λ≤2.2μm, the linearly polarized sensitivity is less than 2%.
Spectrophotometer for measuring spectral transmittance and reflectance of large-aperture optical element
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It is a difficult task to measure the optical uniformity of an optical coating with very large aperture. Here an automatic near-UV/VIS/NIR spectrophotometer has been developed for spectrum analysis of optical coatings on very large aperture optical elements. It can give two-dimensional scanning result of a sample with substrate surface size of 600mm*350mm and 70mm thickness. The testing beam can be s- or p-polarized, at an incident angle from 0° to 70°. The equipment is composed of optical system, mechanical structure, photo-translating module and computer control system. Because of the light deflection after passing through the very thick sample, an integrating sphere and a sphere moving structure was involved. The measuring beam is guided in a quartz fiber with a special interface that can improve coupling efficiency from the monochromator to fiber. The two-dimensional scanning work platform has the position accuracy about 0.05mm and a reproducibility of 0.01mm. The beam incident angle accuracy is controlled within 0.1°. The measurement results show that in the near-UV/VIS/NIR region, the overall photometric accuracy can get 0.1% and 0.2% for transmittance and reflectance, respectively. The wavelength scale is accurate to be within 0.4nm with a reproducibility of 0.05nm.
Improved subpixel analysis algorithm for geometrical superresolution in miniature spectrometer
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This paper aims at reducing the bias distortion in familiar sub-pixel analysis algorithm in miniature spectrometer. The process of sub-pixel analysis is modeled and the fallibility in reported sub-pixel analysis algorithm is discussed. The discussion suggests that an important inducement for distortion is cumulated errors. Hence, an averaged sup-pixel analysis algorithm is put forward. According to the new algorithm, the same iteration is executed twice but in opposite directions and results of the same sub-pixels are averaged. Relative simulation indicates that compare with old ones the new algorithm reduces bias distortion by several times and contributes to an enhanced resolution and wavelength accuracy.
Self-focusing x-ray spectrometer using mica as the dispersive element
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A new crystal spectrometer has been designed and fabricated for measuring laser-plasma x-ray in the 0.99-1.83-nm region. The cleaved mica crystal with 0.2-mm thickness was curved and glued on an elliptical substrate as the dispersive element. The x-ray source and exit slit are respectively placed at the first and second focal point of the elliptical crystal. The x-ray is diffracted by the mica crystal and focused at the exit slit. An x-ray sensitive charge coupled device or streak camera can be easily amounted in the perpendicular orientation to record the space and time resolved x-ray spectra. The spectrometer was tested at the XG-2 laser facility, and the experimental result shows that the maximum spectral resolution is 999.
Space Optics
The optomechanical design of Amon-Ra instrument
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The EARTH-Sun-Heliosphere INteractions Experiment (EARTHSHINE) is a novel space mission designed to answer key questions about how Earth's climate and space environment are influenced by the Sun. One of the four EARTHSHINE instruments called Amon-Ra is a unique Earth reflectance monitor and is a combination of two detectors; one imaging the photon fluxes over the visible wavelength range and the other bolo-metrically measuring global emissions while the satellite orbits about the L1 Lagrange point. Both detectors view both the whole Sun and whole Earth. In order to minimise the differential degradation of front-end optics and detectors, the measurements of the Sun and Earth light are designed to be performed using as many common components of instrument as possible. As the ratio of the radiance emitted from the Sun to Earth's albedo is nearly a factor of 300,000:1, the optics for the Sun channel has to incorporate a smaller aperture and an attenuator. The instrument enclosure is designed to fit into a compact volume including electronics, all mounting feet, connectors, and fixings so that it is expected to make the entire satellite structure compact and cost-effective, whilst meeting the scientific measurement specifications. The optomechanical design we have developed for Amon-Ra is presented in this paper.
An inflatable circular membrane mirror for space telescopes
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The performance of ground telescopes is limited by atmospheric distortion. Nowadays all large ground telescopes adopt adaptive optics for overcoming this limitation. Sending space telescopes outside the troublesome atmosphere might be a natural solution to overcome the atmospheric distortion. However, the cost of development and launch, and the size of launch fairing severally limit this option. Inflatable optics is major candidate for overcoming these technical and budget limits. In this study, we performed thickness optimizations of a membrane mirror for the mirror to be parabolic. Our optimization showed that this optimized mirror is still not good enough for visible observation. However, with limiting the effective optical surface area, the mirror was demonstrated to be used as a primary mirror in infrared bands. In addition, the wavefront errors are also shown to main contributors: piston, defocus and spherical aberrations. Adapting an adaptive secondary mirror with 19 actuators, which has been developed for ground telescopes, could remove the major wavefront errors. Therefore, combining an inflatable primary mirror and an adaptive secondary mirror can be a candidate for future large space telescopes.
A new kind of three anastigmatic mirrors system
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This paper describes the results of the design effort for a new kind of three-mirror anastigmatic system (TMAS) and its tolerance exercise. The system’s focal length is 100mm and the relative aperture is f/10, its total length is nearly f’/3~f’/3.5 and field of view (FOV) is 10° x 1°. The final optical system is a three-mirror unobscured telescope. It achieves diffraction-limited imagery at visible wavelengths. Finally, we can draw two conclusions: 1) design of unobscured optical system is still best approached using fundamental optical design principle; 2) time spent in careful modeling of fabrication, testing will result in more relaxed tolerances and a higher probability of success for the assembled system.
Polarization aberration in resource satellite system
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Polarization aberration is one of the most important factors affecting the performance of optical systems, especially in systems which have many reflectors. The polarization response characters of the reflectors will change the polarization state of the incident light and the polarization aberration will affect the imaging quality of the system. In many resource satellites R-C reflective systems are often used in primary optical systems. The main elements of the R-C reflective systems are reflectors coated with thin films, so polarization aberration must be controlled to improve the imaging quality of the systems. In this paper ZEMAX software is used to realize the simulation of the optical system of a resource satellite and polarization analysis of the system is presented. According to the results of the polarization analysis, the whole optical system is optimized and the ways to control the polarization aberration are summarized. As a result of the study, a conclusion can be drawn that polarization is an important aspect in optical design. To achieve good imaging quality, polarization aberration must be controlled very well, moreover, optical thin film design should be considered while designing optical systems.
Aspheric Optics
Subaperture approaches for asphere polishing and metrology
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This paper summarizes some of QED Technologies’ latest developments in the field of high-precision polishing and metrology. Magneto-Rheological Finishing (MRF) is a deterministic sub-aperture polishing process that overcomes many of the fundamental limitations of traditional finishing. MRF has demonstrated the ability to produce optical surfaces with accuracies better than 30 nm peak-to-valley (PV) and surface micro-roughness less than 0.5 nm rms on a wide variety of optical glasses, single crystals, and glass-ceramics. The MR fluid forms a polishing tool that is perfectly conformal and therefore can polish a variety of shapes, including flats, spheres, aspheres, prisms, and cylinders, with either round or rectangular apertures. QED’s Sub-aperture Stitching Interferometer (SSI) complements MRF by extending the effective aperture, accuracy, resolution, and dynamic range of a phase-shifting interferometer. This workstation performs automated sub-aperture stitching measurements of spheres, flats, and mild aspheres. It combines a six-axis precision stage system, a commercial Fizeau interferometer, and specially developed software that automates measurement design, data acquisition, and the reconstruction of the full-aperture map of figure error. Aside from the correction of sub-aperture placement errors (such as tilts, optical power, and registration effects), our software also accounts for reference-wave error, distortion, and other aberrations in the interferometer’s imaging optics. By addressing these matters up front, we avoid limitations encountered in earlier stitching work and significantly boost reproducibility beyond that of the integrated interferometer on its own.
The intelligent controlling of active lap based on CMAC neural network
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A tool named active lap could fit the aspheric optical surface to grit and polish controlled by CMAC neural networks is introduced. The solution to control the surface of active lap by CMAC neural networks is depicted based on the analyses of active lap control system. The structure and principle of CMAC neural networks model are introduced. A method to test and reconstruct the surface of active lap is put forward. We have the pulse voltage and Zernike polynomial coefficients of surface as input samples and output samples to train the CMAC neural networks until the output meet demand, then the deform of lap’s surface could be controlled by the trained CMAC neural networks. The original data from the micro displacement sensor matrix are interpolated and fitted to reconstruct the surface of active lap, the coefficient of Zernike polynomial fitted form reconstruct data by Gram-Schimdt method is looked as input samples to train the CMAC neural networks. The experiment of three units active lap was made to test the method mentioned above, the feasibility for multi units active lap controlling is discussed base on the simulation of 9 units and 18 units active lap, as well as the analysis of experiment and simulation results.
Algorithm for stylus instruments to measure aspheric surfaces
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A reliable algorithm was developed for the analysis of the machined aspheric surfaces with the stylus instrument. The research has been done as a prior step, with the intent to evaluate the uncertainties in the aspheric surfaces analysis as well as to make the applications that the commercial instruments cannot provide with its own code implemented inside. The algorithm considered two important factors in the instrument-calibration and the aspheric analysis: pickup configuration (pivoted arm) and the stylus radius. It also compensates for the sample tilt and axis offset due to the setup error in the analysis of aspheric surface. The algorithm has been coded by means of C++ and MATLAB. The algorithm was also applied to the real measurement, and compared with the instrument-produced results. Our algorithm found calibration constants better fitting the calibration ball in the instrument-calibration without noticeable cost of the speed. In conclusion, the developed algorithm can cover, and further, shows better performance over the commercial one in both of the instrument-calibration and analysis of aspheric surfaces.
Computer-aided alignment for off-axis asphere null test
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The method of null test is widely used for testing an aspheric mirror. During optical manufacturing process, the mirror has to be moved up and down for testing and fabricating. Because the alignment of null test is difficult and time costing, the efficiency of making aspheric mirror is decreased greatly. In order to solve the problem, we developed a software based on polynomial fitting to calculate the misalignment parameters. By using the software and computer numeric controlled adjusting equipments, the efficiency of testing is increased and the accuracy of test has reached up to λ/40 RMS where λ equals to 632.8nm, which has fulfilled the demand of the designer.
A novel aspheric surface testing method using part-compensating lens
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In contrast to null compensator method in aspheric surface testing, a novel method is presented that uses part-compensating lens and digital moire phase-shift interferometry. Researches are made on measurement principle, design method of part-compensating lens and calibrating lens, and calibrating method. Experiment is made by using spherical surface to simulate aspheric surface testing. The measurement precision is that the P-V value of the testing error can be λ/10. Using the method presented in this paper, the structure of compensator is much simpler than that of null compensator. And one part-compensating lens can be used to test different aspheric surfaces in certain range.
Infrared Optics
Influence of thermal radiations in infrared optical systems
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Based on the basic principle of geometrical optics, an analytical method is presented in this paper. Each optical surface is regarded as an infrared source, and all optical surfaces behind it make up a new optical system. The sampling rays carrying certain energy are used to indicate the thermal radiation beams, and they are traced through the optical system to obtain the energy distribution on the image plane. The influence of thermal radiation in the infrared optical system is further analyzed. An infrared optical system is designed, which has been athermalized. The thermal radiations from each optical surface are analyzed and the superposition result is obtained.
Pupil aberrations control in fish-eye lens with diffractive surfaces
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Optical design for fish-eye lenses usually includes a front meniscus lens that reduces the angles of incidence of chief rays towards the rest of the optics. However it also introduces distortion of the pupil, both shape and position. Thus, pupil aberration are one of the most relevant problems when designing this type of lenses. This paper shows the relationships between image and pupil aberrations and describes the design of MWIR fish-eye lenses that include diffractive surfaces in order to properly control entrance pupil size. The design goal is to achieve a constant pupil area over the field of view.
The optical system for infrared dynamic scene simulation
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This document describes the simulation principle, outlines the design procedure of the projection optics system from predesign to achromatization. The Optical system collimates output from Liquid crystal light valve in 8~12μm and enables an imaging system to be tested out of 20°field of view. The effective focal length of this F/1.5 system is about 113mm. There is sufficient exit pupil distance to match projector exit pupil to the LWIR imagery system entrance pupil. A long working distance between Liquid crystal light valve and the optics system is approximately 120mm. The Modulation Transfer Function (MTF) and the geometric blur spot for three-field position repenting an on-axis point, a full field and an intermediate point show the better performance of the optical system.
Design of aspherical metal mirrors used in infrared thermal imaging systems
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An important factor influencing the image quality of space or military optical systems is that the broad environmental temperature ranges. It would bring some problems on design, fabrication and mounting of the optical system. The ways of getting rid of the problems and improving the image quality of optical systems by using aspherical metal mirrors to the infrared thermal imaging system are presented in this paper. The choice of mirrors materials, the design of mirrors structure, the analysis of factors of influencing mirrors surface figure are discussed. The actual optical system designed in this paper is a Cassegrain objective, and the reflective surfaces of the primary mirror and secondary mirror are conicoid surfaces. The diameter of the primary mirror is φ240mm, the materials of mirrors is aluminum alloys, and the mounting structure is flexible. The aspherical surface of the metal mirror are fabricated by precision diamond turning machine, and the error of the surface figure is less than 0.5μm. The results of the battlefield test show that the infrared system with metal mirrors discussed in this paper has met the optical design specifications.
A novel high-speed optical scanning platform
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Recent advancements in precision engineering have promoted the use of high precision servo mechanism to enhance optical system performance. Present servo mechanisms are able to aid the optical resolution by driving the scanning mirrors to achieve higher resolutions than the traditional imaging systems. To compete with the still imaging systems, the servo mechanisms must achieve very high operation speeds while maintaining highly accurate positioning. This paper introduces a novel, high speed, high precision servo mechanism for the optical scanner. The proposed design uses piezoelectric transducers (PZT) with flexure joints in place of the conventional servo motor drive. The arrangement does not suffer from the backlash problem or the problem with slipping during starting. The study uses the dynamics simulation and finite element analysis (FEA) software for simulation and analysis. The FEA results provide information for the structural prosperities such as the vibration modal type, resonance frequencies, steady state deformation... etc. The analytical data then provide the basis to derive a system model for control synthesis. The dynamic simulation of the control system is accomplished by an integration of the control software with the FEA software. The control output updates the FEA results at every frame time during the simulation. The dynamic simulation results provide all the useful physical properties of the mechanism for prototype design references.
Display Systems
The past, present, and future of head-mounted display designs
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Head-mounted displays present a relatively mature option for augmenting the visual field of a potentially mobile user. Ideally, one would wish for such capability to exist without the need to wear any view-aided device. However, unless a display system could be created in space, anywhere and anytime, a simple solution is to wear the display. We review in this paper the fundamentals of head-mounted displays including image sources and HMD optical designs. We further point out promising research directions that will play a key role towards the seamless integration between the virtually superimposed computer graphics objects and the tangible world around us.
Polarization analysis of projection display system
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In reflective liquid crystal light valve (LCLV) or LCOS light valve large screen projection display system, Philips color separation and color recombination prism system is widely used to make the projection system compact. There are two factors which influence the contrast of projection optical systems. One is the extinction ratio of Polarizing beam splitter (PBS) and the other is the dark-state output of Philips prism system because of geometrical polarization rotations. Optical thin films exhibit inevitable polarization effects at oblique incidence. Here, Geometrical polarization rotation is analyzed in detail. The factors affecting the contrast performance of Philips prism system are quantitatively analyzed. Polarization aberration in this display system is analyzed based on the theory of Jones polarization ray tracing. It can be conclude that the contrast of projection display system is intimately correlated with phase shift difference of the two polarization component. It is concluded that optical design should combine lens design and coating design to improve the contrast and image quality of the projection display system.
Optical Testing II
Ultrahighly accurate 3D profilometer
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We have developed an Ultrahigh-Accurate 3-D Profilometer (UA3P), which, using a new, in-house-developed atomic force probe, has an accuracy of 10 nm. It is capable of measuring corners as small as 2 micro meter in radius and can cover an area up to 400 x 400 x 90 (mm), providing a powerful boost to nano-level processing. A commercial product was introduced in 1994. Examples of the key components made possible by this technology include aspherical lenses (used for a Blu-ray Disc device, a next-generation DVD, digital cameras, cellular phones, optical communications), free form lenses (used for frennel lens common to CD and DVD, laser printer lens, multi focus glass lens, cubic phase plate to extend depth of focus), gigabit semiconductor wafers, hard discs, air conditioner scroll vanes, DVC cylinders. The premiere ultra high-precision three-dimensional profilometer delivers superb performance using a variety of micro-measurements for a wide range of applications.
Real-time measurement of surface roughness based on dynamic speckles
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Dynamic speckles are produced when a diffuse object moving along x-axis with constant velocity is illuminated by coherent light. The diffuse object is considered as a weak random phase screen, statistical properties of dynamic speckles in the Fresnel diffraction field are given in this paper. It is shown that the statistical properties of dynamic speckles depend on the optical condition, surface roughness, and moving velocity of the diffuse object. The parameters describing the property of dynamic speckles extracted from the speckle image, such as fractal dimension, speckle contrast, gray feature of speckle image, binary feature and speckle size. Then according to these features parameters, the recognizing system is established based on neural network technique. Four metallic flat-grinding samples, moving with velocity 4mm/s and 16mm/s respectively, are measured the roughness using this experiment set-up and recognizing system. It’s shown that the average roughness data Ra obtained using the new technique and the Ra obtained using Talysurf are in good agreement. The experimental set-up of this method is simple, fast, and not sensitive to change of circumstance and vibration. Hence, it has great potential for application to real-time measurement.
A new high-precision measurement system used in the image calibration of a large-sized photographic instrument
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The purpose of characterizing the image of large-sized photographic instrument is to make the directionality of three coordinate axises in the three-dimensional coordinate of the image and the directionality of three axises of coordinate in the frame of axes of the instrument keep the same direction. This problem was solved by a high-precision measurement system composed of double-theodolite and a set of communication system. Two cube prisms will be respectively placed on the image surface and the instrument. Every cube prism will stand for a three-dimensional coordinate from the image surface or the instrument. As a result, the interdependence of both coordinates from the image surface and the instrument can be obtained by measuring the interdependence of the both cube prisms with autocollimation survey axiom. In the survey system, two high-precision stations TDA5005 from Leica Company will be selected as double-theodolite and the interdependence of both coordinates can be achieved by moving the station only at one time. Therefore, this measurement system is a high efficient and high-precision surveying method to the image calibration of the large-sized photographic instrument. Based on the experiment, its measuring accuracy can reach arc-second level.
Experimental research on thickness-monitoring techniques of non-quarter films
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The precise control of the film thickness in the film deposition process is the key to depositing optical coating, it is difficult to get ideal film thickness by general turn-point value monitoring. The characteristics of four film thickness monitoring techniques, quartz crystal monitoring technique and common reflectance overshoot-turning point monitoring technique and turn-point monitoring technique with different monitoring wavelength at each layer and mutative overshoot-turning point monitoring technique, are analyzed in this thesis. The contrast experiments adopting the four monitoring techniques respectively to a non-quarter A.R. coating were made under the same technical condition. The experiment results have indicated that mutative overshoot-turning point monitoring technique can get more precise thickness control to non-quarter films than the other thickness monitoring techniques.
Interferometry II
Adaptive phase-shifting interferometer with optical heterodyne vibration measuring and compensating system
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In temporal phase-shifting interferometer, environmental vibrations can induce the wobbling of fringes pattern that usually results in erroneous surface measurement. In order to actively compensating for the external vibration, wave-front phase variation, in proportion to the variation of optical path difference between reference and test arm of the interferometer, should be measured firstly. So, an optical heterodyne interferometric vibration measuring system is embedded in the interferometer, the real-time wave-front phase variation due to vibration is measured by comparing phase difference of two heterodyne signals at 40MHz, one is from reference arm, another is from test arm. An acousto-optical modulator (AOM) is used as optical frequency shifter. After wave-front phase measuring, secondly, a vibration servo compensating system is built. In this system, if real-time wave-front phase is differ from preset phase, an adaptive feedback signal is formed to drive a piezoelectric transducer (PZT), and the PZT drives the standard reference mirror to shift optical path difference in order to pulling wave-front phase to the preset value, thus, vibration is compensated and fringes pattern is stabilized. Thirdly, if preset phase value is periodically changed, a series of phase-shifting interferograms can be sampled. In the end, vibration-compensated effect of this adaptive interferometer is evaluated by an actual optical surface testing, results show this system works very well in the presence of vibrations which amplitude-frequency product is greater than 100 wave-Hertz. Frequency response of this system is restricted by PZT driven reference mirror.
Real-time measurement of refractive index of solution during crystal growth by Michaelson interferometry
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In the real-time monitoring of variations of concentration and temperature of solution by means of contacless interferometry, real-time measurement of changes of refractive index of the solution is prerequisite and essential for post calculation processes. A novel real-time polarized light phase shifting interferometry is proposed in this paper, which was applied to Michaelson type interferometer. Although phase-shifting interferometry provides high spatial resolution, the conventional phase shifting technique by the mechanical movement has not been applied to real-time measurement during crystal growth, due to its physical limitations. We developed a method, using polarized light, and made the real-time measurement possible. The 17% undersaturation aqueous solution of KDP at 20°C was selected as specimen to measure its refractive index during crystal growth. It is found that the present method is a few ten times more sensitive than traditional two-beam interferometry, and more accessible to applications of real-time measurements.
Gauge block parameter measurement through static interferogram using virtual grating moiré technique
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Gauge block parameters are usually measured using Koester interferometer or Twyman interferometer. Conventionally the fraction part of central length of the gauge block within one wavelength may be obtained from static interferogram by fringe analysis. Advanced algorithms should be applied to locate the fringe centers precisely. With phase shifting interferometry (PSI), wavefront reflected from the surfaces of gauge block and its base can be retrieved from several interferograms with a definite phase shift between the adjacent interferograms. Additional hardware, such as PZT phase shifter, should be used to introduce phase shift. In this paper, the gauge block parameters are obtained from the static interferogram with a certain spatial frequency introduced by tilting the reference mirror of the interferometer. The spatial frequency of the actual interferogram can be calculated by FFT algorithm. Then a virtual sinusoidal grating with this spatial frequency is generated in the computer and overlapped on the interferogram to get a moire pattern. By moving the grating 1/4 of the grating period, 4 moire patterns with π/2 phase shift between adjacent patterns are obtained. After removing the high frequency fringes in the above four moire patterns with low pass filtering, four interferograms with accurate π/2 phase shift between the adjacent ones are remained. Then the wavefront is retrieved with 4-bucket algorithm. In this method, the static interferogram is analyzed with PSI algorithm but there is no need to have phase shifter. Besides, the phase shift is introduced mathematically to avoid the associated error. The actual interferograms are processed and results are obtained.
Calculating Strehl ratio through radial shearing method
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The approximate Strehl Ratio expressions that need only the wave phase distribution is not appropriate in the laser fusion system when the phase has great aberration. The accurate Strehl Ratio value need both the phase and the amplitude distribution information. The paper provide a method of reconstructing wave phase and amplitude
distribution by a single radial shearing interferogram. The radial shearing interferometer based on spatial phase modulation is simple and stable, needs only one interferogram. The principle and structure of cyclic radial shearing interferometer are briefly discussed and the process of spatial phase modulation, Fourier transform method and wavefront reconstruction are analyzed. It also illluminates the physical meaning and establish the mathematical model. The process of getting SR value is simulated by computer. The simulation result indicates that the RMS error of the reconstructing wavefront can achieve λ/100.
The measurement of large workpiece diameter of axle with double-laser interferometer
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The collimation of the measurement point on the inner and outer diameters of a large workpiece is a key technology in large diameter measurement, and it is a measuring difficulty yet to be well resolved home and abroad. This paper applies highly stabilized light produced by laser collimator to collimate the photoelectric detectors on the two magnetic localize is each adhered to an end of the diameter of the piece, meanwhile, use the interferometer to measure the distance between the center of the two photoelectric detectors, and obtain the diameter by geometric computation. Both the theoretical analysis and the experiment showed that the method is practical, with relatively high precision, and the relative error of the measuring system was less than 5×10-6, which is superior to the traditional mechanical measurement.
Algorithm study of the measurement of the radius of curvature of fiber optic connector end faces
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With the rapid development of fiber communications, the fiber optic connector has become an indispensable no-source device, among which PC-type connector is most commonly used. As radius of curvature (ROC) of the connector end face is one of the three main geometric parameters affecting insertion and return losses, how to measure accurately the ROC has become an important issue in the field. In this paper, an algorithm, overlapping averaging 4-bucket method (OAF), is introduced to measure the parameter. Correspondingly, calculation of the phase principal values of the object wave-front and reconstruction of the spherical profile of the connector end face are analyzed, with simulation results given. Also analyzed is the influence of the shifting error of the phase shifter on the ROC measurement, with a curved surface figure for their relationship obtained. Meanwhile, a comparison is made between the errors developed by the 4-bucket algorithm (FBA) and OAF. It is indicated by the results that, OAF is superior to FBA in the suppression of the shifting error, and that, over a general range of calibration error and nonlinear displacement error both equal to or less than 8%, the ROC measurement error with OAF is less than 2.3×10-4.
Profilometry
Dynamic 3D profilometry with dual-acousto-optic fringe projection
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A three-dimensional (3D) profilometry based on a dual-acousto-optic fringe projection is reported in this paper. The fringe projector is able to generate fringe patterns with different optical sensitivities and therefore can handle the object surface with complex geometry and topology. It is also qualified for video-rate 3-D profilometry of arbitrary shape objects. By using two acousto-optic deflectors (AODs), the projector can generate a time-series, frequency-varying fringe patterns by use of the AO interaction effect. The two AODs are driven by the radio frequency (RF) signal with the same frequency. Changing the RF frequency leads to the change of the period of fringe patterns and, therefore, different sensitivities. In practice, the changing rate of sesitivity is limited by the frame rate of the detector, e.g. CCD, so it makes a dynamic 3-D profilometry possible. Experimentally, we project a sequence of spatial frequency-varying fringe patterns onto the test object surface. Then, a CCD camera simultaneously acquires the phase-modulated fringe patterns accordingly. With a sequence of phase measurement in a progression of fringe periods, an enhanced scheme for phase unwrapping algorithm is implemented in a recursive manner. The object surface with complex geometry and topology can be reconstructed in this way. Experimental results are also given to validate this approach.
Research on the color 3D profilometry and parameter calibration technology
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A completed system for color 3D object measurement is presented, which is composed of a line-structured laser sensor and a two-axes translation stage. As well as the mathematics model of 3D measurement based on line-structured laser method is founded and two groups of unknown-parameters are derived, namely the camera parameters and the light-plane parameters. The color 3D data (xi,yi,zi)-(Ri,Gi,Bi) is obtained by merging the color data (Ri,Gi,Bi) and 3D (xi,yi,zi) data according to the corresponding pixel coordinates (ui,vi) of the stripe. A kind of circle pattern is applied in the calibration on both groups of parameters, however the way to acquire the control points by use of the pattern is different in each calibration process. In the calculation of light-plane calibration, an unrestricted object function is constructed to ensure the orthogonal character and accuracy of the parameters. In order to verify the measurement accuracy of the calibrated system, the measurement on a standard jig is performed with the accuracy better than 0.1mm. The result shows the parameters calibration is reasonably effective and reliable. The system is developed for the antique digitization, game development, etc., and it will have a promising future.
Wavelet transform method for phase demodulation of carrier fringe pattern
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A new method for analyzing the phase distributions of carrier fringe pattern has been presented. The discontinuities and spurious data has been and still is a cumbersome concern, it is hard to reconstruct the phase by phase demodulation based on phase gradients. The approach that we here introduce to solving this problem is to utilize Gabor transform, a tool excelling for its multiresolution in space-frequency domain, to analyze the phase distributions. The experimental results demonstrate the validity of the proposed method.
Novel Designs
Light-weight objective lens for DVD pickup
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The size and weight of the pickup head will influence the form factor and the bandwidth of DVD. A MEMS-type DVD pickup was proposed, in which the objective lens will be manipulated with a micro actuator for focusing. A high order diffractive objective lens has been designed specially for meeting the request on reduced weight by optimizing the surface relief profile of each zone one by one. The simulation by ray tracing tool shows a well corrected geometrical aberration and a near diffraction limit focal spot. The lens is expected to be produced with gray scale mask photolithography, and the weight will have only one third of that of its refractive counterpart.
Combo HD-DVD and DVD pickup head with prisms
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We proposed a combo design of pick-up head used prism to shorten the geometrical size and reduce the optical components. We apply a rhomboid beam splitter to separate two diodes in the design for the optical pick-up head of DVD and HD-DVD.
Microstructure inspection endoscope design
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A microstructure inspection endoscope, based on directly imaging, is proposed. It is designed for detecting defects on the surface of optical fiber end. It is matched with FC or SC female fiber connector. The inspection head of the endoscope can be put into a 2.5-millimeter-diameter micro-pore. Its numerical aperture is not restricted by tiny dimension of object lenses. System resolution is increased to 600 line-pairs per millimeter. The endoscope consists of object lenses, scanner slab and kohler illumination system. The design provides possibility of various utilities such as aiming at a smaller subject by micro optical scanner and modeling the surface by tri-dimensional vision. And the optical system includes low-magnification lenses and high-magnification zoom lenses. Rough observation at low-magnification and particularly inspection at high-magnification are provided. The instrument has the advantages of high identification, compact configuration and flexible manipulation.
A new superresolving design for laser beam shaping
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In many applications, one repeatedly encounters the problem of laser beam shaping. Shaping laser beam means converting an incident wave front into a desired wave front in the output plane. Superresolution technology can be used for achieving smaller spot than an Airy spot which is the limit of resolution of optical system caused by diffraction. In this work, superresolution technology is extended for laser beam shaping. The aim of the research is to design a new phase-only superresolving element by using local direct search optimization algorithm. The results show that better superresolving performances of our phase elements are obtained compared with those of phase plates of references. The phase element we design is a new type varying in discretely continuous way and is regarded as a hybrid combination of continuous and discrete phase type, whose phase distribution is composed of two parts: the first part is a continuous phase profile; the second part is a constant phase step. The phase steps of this phase plate are different in the different zones. More importantly, it is possible that desired flat-top wave front is obtained by using this design. Therefore, this design provides a novel tool for laser beam shaping.
Performance analyzing and parameter revising for soft x-ray multilayer mirrors at E=60eV
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In this paper, a Mo/Si multilayer mirror of normal incidence at E=60eV was firstly analyzed. From the measurement curves of a small angle x ray diffraction, the property of interfaces and the parameters including period thickness and roughness were gained. Through the analyzing, we found that performance is not good, the peak reflectivity is low and is not correspond with 60eV. Secondly, a revised design using Simulated Annealing arithmetic was applied in it. The revised design results shows a promising mirror at 60eV and are consistent with the results of the program of optical coating technology R&D center in Shanghai Institute of Optics and Fine Mechanics.
Integrated Optics
Nonparaxial Fresnel diffraction from oblique end facets of optical fibers
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When optical fibers are connected with other optical or opto-mechanical components, free space propagation phenomena of the light emitted from cleaved end facets of fiber need to be precisely known to maximize coupling efficiency. Besides, optical fibers are widely used in interferometers design as point-diffraction sources to replace conventional pinholes, in which case the far-field wave front of the light emitted from fibers is of major concern. End facets may be cleaved normal to the optical axis of fibers or with oblique angles to suit specific purposes such as anti-reflection or propagation direction alteration. In this investigation, diffraction from oblique end facets of single-mode fibers is studied with emphasis on Fresnel propagation in nonparaxial zones based on the Rayleigh-Sommerfeld scalar diffraction theory. The result is a closed-form explicit solution expressed in terms of spherical coordinates, which enables to determine the propagation field generated over an entire hemispherical observation surface. In comparison to exiting solutions of numerical or infinite series forms, the explicit solution obtained in this investigation saves a considerable amount of computation time and provides better estimation accuracy. Finally, as an example, the wave front sphericity emitted from an oblique single-mode fiber used in a new design of the Fizeau interferometer is determined and discussed in detail.
The algorithm comparison for solving eigen problems in open optical waveguides
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In this paper, based on the Rayleigh quotient and its generalized Rayleigh quotient, two treatments are developed to solve the complex eigenvalue problems, which arise from the analysis of the optical wave propagation in Slab waveguides with some perfectly matched layers. Numerical examples illustrate that these treatments are efficient and feasible, and the generalized Rayleigh quotient method is better than the Rayleigh quotient method for some eigenvalues with smaller norm.
Adaptive polarization mode dispersion compensation system based on DOP as the feedback control signal in 40Gbit/s OTDM system
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The principle of adaptive polarization mode dispersion compensation based on signal DOP as the feedback control signals was analyzed. A 40Gbit/s adaptive PMD compensation system was developed and the experiment of second-order PMD compensation was performed. The results show that the system can compensate second-order PMD adaptively with the compensated DGD value up to 30ps within 100ms. The PMD monitoring technique adopted in the experiment was based on measuring DOP, which showed the characteristic of bit-rate independence.
Poster Session
APS star sensor performance assessment through real-sky observation experiments
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CMOS APS based star tracker is a new generation of attitude sensor. An APS based autonomous star tracker has been proposed. This paper gives a primary demonstration of the software performance of the proposed star tracker, through laboratory and real night sky experiments. The star pattern recognition algorithm in the software protocol uses a quick search and robust match strategy and can perform independent star identification without prior attitude knowledge. The laboratory experiments validated the whole sky independent star pattern recognition algorithm and showed a comprehensive influence of errors and noise on the software performance. The real night sky experiments tested the sensitivity of the APS star sensor and validated the feasibility of the star identification and attitude estimation algorithm. In this paper, the structure and procedure of the software is described. The experiment system setup is introduced and the results of the laboratory and real sky experiments are presented and discussed.
Using spherical aberrations of a singlet lens to get a uniform LED illumination
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In order to get a simple LED illumination system with a short length, the LED needs a large irradiant angle (2ω = 90°) and the lens needs a large aperture. This would conduce a severe non-uniformity on the illuminated area and a very low F-number. So it is rather difficult to design a singlet lens for LED illumination system with a better uniformity in certain area because of the non-uniform irradiation of the LED and the contradiction between the focal length and the aperture. For an on-axial point source, the spherical aberrations in different apertures can change the propagating direction of the rays; therefore it is possible to get a uniform illumination with the help of spherical aberrations. Light density function on the illuminated plan is deduced, and the merit function for uniform illumination in certain area is defined in this paper. By using the optical design software ZEMAX EE, the search of the optimal value for the given focal length is done. The computer simulation results show that by producing spherical aberrations correctly a better uniformity illumination can be obtained on the illuminated area in certain distance successfully.
Diagnosis of the electron temperature in dielectric barrier discharge by optical emission spectroscopy
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Glow dielectric barrier discharge appears as an attractive solution to realize near atmospheric pressure cold plasma process suitable for all the surface treatments including thin film coating and material making. Such development requires a large understanding of the dielectric barrier discharge (DBD) physical and chemical process. The objective of this work is to contribute to that understanding. In this paper, we report the results of the measurement of the spectrum from 690nm to 800nm in DBD in argon. The electron temperature Te has been estimated using intensity ratio method by optical emission spectroscopy under difference experimental conditions. According to Local Thermodynamic Equilibrium (LTE) theory, the electron temperature Te can be assumed equal (equals) to the excitation temperature Texc, namely Te=Texc=T. Therefore, the plasma temperature T can be determined by comparing the relative intensities of spectral lines from the same element and ionization stage. The spectral lines 763.72nm (2P6→1S5) and 772.63nm (2P2→1S3) of Ar atom are chosen to estimate the electron excitated temperature. The experimental results show that the electron excitated temperature is in the range of 0.3-8eV in Ar under different pressures. The results also show that the electron excitated temperature increases with the decreasing of the applied voltage. The results provide a reference for the controlling of DBD and are of great importance to the industrial applications.
High-speed measurement of an air transect’s temperature shift heated by laser beam
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Laser beam heat the air on the optic path, Beam-deflection optical tomography is a non-intrusive method to measure the 2-dimension temperature distribution in the transect. By means of linear Hartmann Sensor at the rate of 27kHz, the optic path was heated by a 2.7μm HF laser, continuous and high time resolution gradients of optic phase were obtained. the result of analysing and calculation showed the temperament shift in the heated beam path was not higher than 50K when the HF laser power was 9W. The experiment showed that it is a practical non-intrusive temperature shift measurement method for a small area aero-optical medium.
Calibration of numerical aperture effects in double beam interferometers
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The numerical aperture (NA) of the double beam interferometers (DBI) can affect the accurate measurement of surface profiles. Based on the double beam interference microscope imaging theory, the fringe spacing will vary wide nonlinearly with the increasing of numerical aperture. The double beam interferometers require oblique incidence illumination, including Michelson, Mirau and Linnik types. The intensity distribution of the illumination across its stop is constant so the correction factor depends mainly on the NA in the Michelson and Linnik interferometers. The correction factor expression is derived in the Michelson interferometer. The reference surface is a central obscuration in the beam, which will reduce the effective numerical aperture in the Mirau interferometer. At the same numerical aperture, larger central obscuration has a much effect on the correction factor. The correction factor expression is determined by considering the influence of central obscuration and oblique incidence in the Mirau interferometer.
LD pumped Nd:YAG/KTP intracavity frequency-doubled 1.2 W CW red laser
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This letter reports the CW red laser radiation at 659.5 nm by intracavity frequency doubling a side pumped Nd:YAG laser with a KTP crystal (type II phase match, Θ=59.8°, Φ=0°). The thermal lens effect related to the laser crystal is analyzed and parameters of the three-mirror folded cavity are calculated. To enhancing the high gain at 1319 nm of the operating wave of Nd:YAG, the reflectivity of the mirrors is designed, and the red laser radiation at 659.5 nm is achieved by intracavity frequency-doubling. The generation of 1.2 W of the CW red laser beam is obtained with 260 W pumped power.
Multiresolution 3D imaging with temporal sequential fringe projector
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In order to implement 3-D imaging of objects with large height discontinuities and/or surface isolation, we present a novel 3-D imaging system based on temporal sequential fringe projector to provide multi-resolution 3-D reconstruction. To recover the range data of such a surface, an enhanced scheme for temporal phase unwrapping procedure is proposed. We also describe methods for extracting the color texture corresponding to a range image. Experimental results are given to illustrate the validity of our proposed method.
Hybrid diffractive-refractive optical system design of head-mounted display for augmented reality
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An optical see-through head-mounted display for augmented reality is designed in this paper. Considering the factors, such as the optical performance, the utilization ratios of energy of real world and virtual world, the feelings of users when he wears it and etc., a structure of the optical see-through is adopted. With the characteristics of the particular negative dispersive and the power of realizing random-phase modulation, the diffractive surface is helpful for optical system of reducing weight, simplifying structure and etc., and a diffractive surface is introduced in our optical system. The optical system with 25 mm eye relief, 12 mm exit pupil and 20° (H)x15.4° (V) field-of-view is designed. The utilization ratios of energy of real world and virtual world are 1/4 and 1/2, respectively. The angular resolution of display is 0.27 mrad and it less than that of the minimum of human eyes. The diameter of this system is less than 46mm, and it applies the binocular. This diffractive-refractive optical system of see-through head-mounted display not only satisfies the demands of user’s factors in structure, but also with high resolution, very small chromatic aberration and distortion, and satisfies the need of augmented reality. In the end, the parameters of the diffractive surface are discussed.
Research on testing output signal-to-noise ratio of image intensifier
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Image intensifier is the kernel of the low-light-level image device. Output signal-to-noise ratio is one of its important parameters which can reflect the image intensifier’s imaging quality. Traditionally the test of image intensifier’s output signal-to-noise raito is realized by using a multiplier phototube, which method only gets the output signal-to-noise ratio of temporal field and can not evaluate the effect of the space structure’s nonhomogeneity of the fluorescence screen in the round. In view of these defects, the traditional method is replaced by a new one based on the three-dimensional noise theory. In this paper, a set of test formulas of output signal-to-noise ratio in spatio-temporal field which can roundly evaluate the image intensifier’s imaging quality are deduced, a test system based on the planar CCD image gathering and processing system with high sensitivity and low noise is designed. By using digital image processing technology based on Visual C++ and Matlab, a part of tested data of some home image intensifiers are given and subsequently some 3-D graphs of noise which can describe the spatical-temporal field’s imaging character in different brightness gain are drawn. The practical results can show that the new test method is rounded, accurate and visualized.
New methods for determining optical constants of thin films from single measurements
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Optical spectrum measurements are commonly used for the routine determination of thin film optical constants. This paper presents some new methods of evaluating transmission spectrum data only, leading to thickness and values for the complex refractive index by optimizing the physical thickness, refractive index and extinction coefficient, such as step constrained optimization approach, subsection fitting, accelerating optimization model (namely, some dispersion formulae are adopted to comply with the physical constrains set), etc. The methods applies to all kinds of transmission spectra and do not rely on the existence of interference fringe patterns or transparency. Through a lot of experiments of the films Ta2O5, TiO2 under different IAD (ion-assisted deposition) conditions, the deviation between the measured and the theoretical spectra data is less than 0.53% in p-order model merit function (p=2), which shows that these methods are reliable. Now, we have gotten the thickness and complex refractive index of DLC (Diamond-Like Carbon) films on BAK7 glass substrates by these methods successfully. Examples are presented and discussed.
The rectifying device for optical axis of sighting devices
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The combination photo electronic sighting device usually composed of different optical devices, including telescope and low light level night vision device or infrared thermal imaging system. Every optical axle of the optical device of the combination sighting device is needed to be parallel. When a target away enough from the sighting device is observed, if the images of the target locate on the center of the field of the vision of the different optical devices, it shows that the axis are parallel. According to this principle, a rectifying device for optical axis of sighting device is designed. It includes off-axle paraboloid reflector, the target of cross line, light sources, precision modifying devices and other devices. The target of cross line is put on the focus of the off-axle paraboloid reflector, thus it forms a parallel light beam through the off-axle paraboloid reflector, the sighting device is immerged in the parallel light beam. The observing effect is like a target of long distance. The target is connected with a precision modifying device, by moving modifying device, until the image of the target coincide with the center of the field of vision of every optical device, whose degree of deviation of the optical axle can be calculated. The paper gives the structure of the rectifying device and the way of testing. The parameters of the device is given too.
Optical design of dual-axis fluorescent confocal scanning system for biochip
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As a new research field, biochip has enjoyed its rapid development in the past 10 years. Today, most of the biochip scanning systems are fluorescent confocal scanning systems. The conventional fluorescent confocal scanning system has few limits in some kind of biochips, such as cell-chip, tissue-chip and so on, because these biochips need a long working distance to add medicament or reagent in it real-time. The longer the working distance is, the more convenient to add the medicament or reagent. However, the conventional fluorescent confocal scanning system can’t have long working distance, especially when the system has high resolution and large aperture. In this paper, a dual-axis fluorescent confocal scanning system with a long working distance and high resolution has been presented. In the dual-axis fluorescent confocal scanning system, the incident light is tilt to the axis, which can decrease the bleaching of fluorescent induced by the laser. The working distance of the system is 15 mm and the numerical aperture is 0.35. The phase aberrations of objective lens, including the spherical aberrations and the chromatic aberrations corresponding to wavelength 532 nm, 570 nm, 635 nm, 670 nm, are corrected very well. The encircled energy diagram of the lens is good to the diffraction limit. The image spot diagram, the ray aberration fan diagram, the transverse ray fan plot and the modulation transfer function, are studied also. The image quality of the system designed in this paper is good enough to meet the practical requirements.
An instrument for surface roughness measurement of optical thin films
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A total integrated scattering (TIS) instrument is presented. Its basic structure, theory foundation, and measurement principle are introduced. The surface root mean square (rms) roughness of single silver films on BK7 glass substrates is measured by employing this instrument. The results agree well with the data obtained by the optical profilometer and the atomic force microscope (AFM).
The application of randomized Hough transform on testing circular bubble
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Today, circular bubble is tested mainly by manual work that leads to lower efficiency and limited precision. A new testing method based on CCD image system is proposed in which the bubble is laid on an inclinable workbench, and then digital images of the bubble are captured by CCD image system. After the displacement between the center of the bubble and the scale circle is detected through a revised randomized Hough transform, the scale unit and the sensibility of circular bubble can be obtained.
Optical design of resource satellite system
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The optical system of an infrared multi-spectrum scanner used on the resource satellite is presented in this paper. The principles of spectrum-dividing and imaging, the designing of optical system, the optimization of the assemblage and the adjusting of relay optical system are discussed. According to the general principles of infrared systems, R-C system is used in designing of the primary optical system. There are two methods to design the relay optical system, one of which consists of a complex prism and the other uses a binary optical element. The results and imaging quality of the two methods generated by ZEMAX are given. In the system using complex prism, each wavelength band consists of an R-C system. The diffractive system uses diffractive-refractive hybrid systems to divide spectrum, image and achromatize. The results show that the image quality of the designed system is good enough to meet the practical requirements.
Concept and application of virtual normal surface
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A new optical surface, Virtual Normal Surface (VNS) model is constructed in concept. With the special surface type, a lens in double-pass can be turned into single pass configuration in optical software, which makes the modeling the optical system easier. The VNS is realized in optical software ZEMAX. The normal aberration of an aspheric surface is simulated and visualized in ZEMAX with the VNS. VNS can also be used in modeling null corrector, which makes optimizing, applying constraints to lens data, and tolerance analysis more quickly and easier.
Measuring research on the optical system’s resolution with the radial target
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With the development of Charge Coupled Device (CCD) technology, the method to measure the optical system’s resolution with the machine sight has been applied widely, which can overcome the factor of subject error that will exist when adapting human being’s eyes to measure the resolution. With the radical target to measure the optical system’s resolution, it has many merits such as the measuring equipment is simple and the operation method is convenient. The measuring process is realized with a collimator and a CCD camera through adopting necessary image processing methods in the paper. The matching problem between the machine sight and the human being’s eyes when judging the optical system’s resolution is analysed firstly in the paper. And the critical contrast is got, which should be adopted when applying the machine sight to measuring the optical system’s resolution. Next step is to find where the resolution is nearest to the critical contrast in the target image. With the method present in the paper, we get it. So the resolution of the tested equipment can be figured out. Through contrastively analyzing the resolution data which is obtain with conventional method and with the method presented in the paper, it shows that the method to measuring the optical system’s resolution with radical target in the paper is viable completely.
Lens design for holographic data storage systems
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A pair of cascade lenses, a Fourier-transform lens and an imaging lens, is the key component in a volume holographic data-storage system (HDSS) for writing in and reading out the information in holographic recording material respectively. For a high-density holographic data-storage system, performances of these lenses are critical. In order to obtain precise input and output information, and reduce the bit-error rate in the retrieved data, the accurate pixel matching between the whole high-resolution page of SLM and CCD must be ensured. To meet these requirements, in this paper the design of this lens is discussed in detail. In this paper we designed the lenses of unsymmetrical structure and compact profile, and the maximal image distortion of the lens less than 0.01%, and the MTF value at the spatial frequency 40 LP/mm greater than 0.5 over the whole view-field. Other aberrations such as spherical aberration, field curvature, comatic were well corrected. The lens can realize pixel matching between 1024x768 of SLM and CCD. Furthermore, the effect of the manufacture accuracy of the lens on its image quality was analyzed, based on which the optimum parameters and manufacture/assembly tolerance are given.
Study on computer-aided alignment method
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A computer-aided alignment procedure is described, based on an off-axis three-mirror system. The relationship between the tilt and decenter variables is analyzed and the primary aberrations introduced by the variables are calculated. By eliminating the correlated variables, the alignment solutions are determined and damping factor is not needed. The processes of the method are as follows: 1) the correlation among variables is obtained by calculating the condition number of the sensitivity matrix for optical systems. 2) the alignment variables and magnitudes are gotten by eliminating correlated variables. The results simulated by a computer show that it is theoretically feasible to determine the solution by only one iterative. It can not only meet the precision requirement, but also accelerate the convergence of alignment solutions. This method is realized by compensation among variables, so the variables are reduced and the time of alignment is saved.
Fast Ronchi test base on a liquid crystal display
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A combination of a small liquid crystal display, conventional Ronchi test and fringe-scanning test is used to measure an aspheric wavefront or a large wavefront aberration system, faster and more exacting. Instead of a common grating and a step-motor, a movable image of grating is showed in a liquid crystal display. This gets rid of the error that caused by grating moving or motor rotating. A formula of the light intensity of the two dimensional grating, which a liquid crystal display owns, is derived. 12-step phase-shifting algorithm is used to test a lens, and the large wavefront aberration of the lens is restored.
Measurement of photoelectron behavior in K4Ru(CN)6-doped AgCl emulsion
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Photoelectron decay characteristics in latent image formation process directly reflect photographic efficiency of silver halide crystals. Dopants can be substitutionally incorporated into AgX crystals and influence the photoelectron action by introducing appropriate electron traps. Long photoelectron lifetime can improve the photographic efficiency of intrinsic or unsensitized grains. In general, AgCl are intrinsic or unsensitized emulsion. Cubic AgCl microcrystals doped with K4Ru(CN)6 were measured by microwave absorption and dielectric-spectrum technique. Measurement of the photoelectron decay process as a function of doping position and concentration can provide important information about the electronic properties. The experimental results show the photoelectron decay time at room temperature is more or less longer than undoped samples. The photoelectron decay time increases with the doping concentration increasing and with the doping position closer to the core except for position 30%Ag and over high concentration 3.21x10-5 mol/molAg. When doping position is 30%Ag, the photoelectron decay time reaches its maximum at the doping concentration of 1.5x10-5 mol/molAg. At doping concentration 3.21x10-5 mol/molAg, the photoelectron decay time reaches its maximum at the doping position 60%Ag. Through studying the photoelectron decay behavior, we can know the doping can improve the image quality of AgCl emulsion.
Test aspheric with CGH based on a liquid crystal display
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A combination of computer generated hologram (CGH) with a small liquid crystal display, phase-shifting detection, and Twyman-Green interferometer is used to test an aspheric. This method resolves the problem of real-time produce CGH. In the paper, a method of producing real-time computer generated hologram is proposed in which a small liquid crystal display is adopted as a recording material. The making principle of the real-time computer generated hologram is described. The experimental result is better.
Sensitive time-resolved fluorometer
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With the use of lanthanide trivalence ion and its chelates for marking substance, Time-resolved Fluorescence Immunoassay (TRFIA) is superior to RIA in sensitivity, speciality, stability. And it has become one of the hotspots in the field of labeled immunoassay application. In this paper, a sensitive time-resolved fluorescence immunoassay instrument made by us was presented. In the device, a pulsed Xenon lamp of flash frequency 1kHz was adopted as exciting light, and the peculiarities of long lifetime and big Stokes about lanthanide trivalence ion and its chelates was utilized for the application of time-resolved and spectra-resolved technique. Thus the influence of scattering light and short-lifetime fluorescence was removed. By testing, the sensitivity is 10-12mol/L (when Eu3+ was used for marking substance), examination repeat is CV less than or equal to 5%, examination linearity is from 10-8mol/L to 10-12mol/L, correlation coefficient r=99.9%(p=0.0001). In a word, the instrument is advanced for ultrasensitive detection of antigen and antibody, and many other aspects.
Modified SART with changing relaxation factor (CRF-MSART) applied to optical CT in finitely orthogonal views
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Optical Computed Tomography (OCT) is available for 3-D distribution of solution’s refractive index. The 3-D distribution can be fitted up with divers 2-D slices. Thus, the discrete mathematical model of 3-D refractive index data reconstruction can be framed in a linear ill-posed problem. We proposed a practical reconstruction algorithm, Modified SART with Changing Relaxation Factor based on Simulated Annealing algorithm (CRF-MART), which is a modification of Simultaneous Algebraic Reconstruction Technique (SART). Furthermore, a computer simulation of the reconstruction algorithm was taken in the case of incomplete data. It is shown that reconstructed results have better smoothness and smaller residual, which are a good approximation to the true value.
In situ observation of crystal growth and concentration variation by spatial filtering method
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A spatial filtering method was developed for in-situ observing crystal growth and concentration variation. We insert a polarizing filter between the growth chamber and objective lens for eliminating the transmitted light through the solution. The dark background introduced by polarizing filtering method is advantaged for observing the sample. Due to the birefringence property, the image of crystal is contributed by extraordinary-ray and ordinary-ray through the crystal and analyzer. Meanwhile, a high pass binary amplitude filter is inserted on the back focal plane of the objective lens for attenuating low-frequency information and transfer phase information of the object to intensity information of the image. The image intensity has become squarely related to the phase shift φ of the crystal and solution. It is possible to observe the phase object and also to inverse the image contrast and strengthen the image edge. The method has been successfully used to observe not only crystal morphology and details but also concentration field variation around the growing crystal.
A novel interference fringes software counting method
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Conventional interference fringes counting methods often process two sinusoidal interference signals with a phase difference of π/2 to realize fringe-counting. But when the signals fluctuate in half a period of the signal, the conventional fringe-counting method sometimes produces direction-distinguishing mistakes, then resulting in counting errors. To address the problem, this paper presents a novel interference fringes counting method that uses software to distinguish the forward or backward direction of interference fringe and to count. This fringe-counting method can accurately distinguish the moving direction induced by the fluctuation of interference fringes, so it has the advantages of exact counting, intelligence and reliability. An experimental setup based on a Michelson interferometer is constructed to demonstrate the utility of this fringe-counting method for displacement measurement, and experimental results with a range of 1036mm is presented.
Performance test of focusing optics based on the Hartmann principle
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The performance inspection of focusing optics, such as focusing lens and focusing assemblies, is of great importance in the machining of optical elements, alignment and regular maintenance of optical facilities. Currently, however the interferometric method and the knife-edge method used normally for the measurement of the large-aperture surface have limitations for the test in the large optical equipment. To solve the problems, a scanning Hartmann inspection apparatus based on the Hartmann principle for focusing optics performance test has been developed. In this paper, the experimental setup and test principle are described, experimental results and analysis are given, and the improvement plan further to obtain better test capability is briefly presented in the end.
Novel phase unwrapping algorithm of DSPI for complex and discontinuous structure
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A novel phase unwrapping algorithm of DSPI for complex structure is proposed in this paper. An image of the object to be measured with very high contrast can be obtained by the subtraction of two speckle pattern interferograms, whose optical phases are opposite. The complete image area of object to be measured can be correctly obtained from this high contrast image. By controlling the phase unwrapping procedure to be inside the image area of the object, the wrapped phase map of complex structure can be unwrapped. This novel phase unwrapping algorithm makes DSPI be able to be used to measure the complex structure in practical engineering, and will enlarge the application field of DSPI.
The design and fabrication of an inverted IR optical trap
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Optical tweezers offer the unique ability to manipulate particles dispersed in a liquid medium without any mechanical contact. It can trap, move and position a wide variety of living cells and sub-cellular particles. The nature of the technique has led to its predominant use in the fields of medicine and microbiology. On the other hand, different biomedical experiments require the traps with different structures and characteristics. Commercial optical tweezers are very expensive and they can’t meet the demands of some special experiments. In this paper, the authors describe a detailed recipe for fabrication of an inverted optical trap. The system uses a single mode laser with the wavelength of 1064 nm so as not to damage the living organisms. The system has a platform whose temperature is tunable at a range of 20-40°C and can be stabilized by a controller. The system is also has a video device. The significant advantage of the system is low cost and easy to be operated. It especially fits the labs that are short of fund but interested in the application of optical trap in research of living cells. By means of the system, the authors do the experiments on control over the neuronal growth successfully.
Analysis of alignment error in asphere testing using a corrector
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The characteristics and effects of alignment error on test results are analysed in this paper. The mathematical model are established, the least square method is used to determine the misalignment. Procedures are presented that allow for separation of misalignment from misfigure in asphere testing. The misalignment-induced aberrations by corrector and the support of the mirror can be calculated and subtracted from segment interferogram so that only true misfigure remains. The accuracy of the system can reach up to 0.028λ(λ=632.8nm).
Optimizing parameters for magnetorheological finishing supersmooth surface
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This paper presents a reasonable approach to this issue, i.e., computer controlled magnetorheological finishing (MRF). In MRF, magnetically stiffened magnetorheological (MR) abrasive fluid flows through a preset converging gap that is formed by a workpiece surface and a moving rigid wall, to create precise material removal and polishing. Tsinghua University recently completed a project with MRF technology, in which a 66 mm diameter, f/5 parabolic mirror was polished to the shape accuracy of λ/17 RMS (λ=632.8nm) and the surface roughness of 1.22 nm Ra. This was done on a home made novel aspheric computer controlled manufacturing system. It is a three-axis, self-rotating wheel machine, the polishing tool is driven with one motor through a belt. This paper presents the manufacturing and testing processes, including establish the mathematics model of MRF optics on the basis of Preston equation, profiler test and relative coefficients, i.e., pressure between workpiece and tool, velocity of MR fluid in polishing spot, tolerance control of geometrical parameters such as radius of curvature and conic constant also been analyzed in the paper. Experiments were carried out on the features of MRF. The results indicated that the required convergent speed, surface roughness could be achieved with high efficiency.
An experimental research on measuring fracture toughness of high-temperature alloy by holographic moiré interferometry
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The fracture toughness of high-temperature alloy material under high-temperature is tested with the laser moire interfrometric device. The zero-thickness grating is etched on the surface of test piece by electrochemical method directly, expanding the research space of high-temperature alloy’s moire interferometry. The moire fringe is collected and analyzed by CCD imaging system of computer, the test result that indicates imaging quality and measurement precision of moire interferometry are improved.
A new finding about the coupled fringes of off-plane displacement and slope in shadow moiré and its optical analysis
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The traditional concepts considered that only off-plane displacement can be obtained by the shadow moire method, but the slope moire fringes must be obtained from the specimen with mirror surface by the reflection moire method, etc. However, our recent experimental results reveal that the off-plane displacement fringe and the slope fringe appear together in a shadow moire pattern under experimental definitions. The basic principle and related experiment techniques are presented firstly in this paper. Two examples, a thin hyperboloidal shell and a thin cylindrical shell with local buckling, are given to demonstrate the actual coupled moire fringe patterns. Moreover, two distribution curves of δW/δx and W along asymmetry axis on the thin hyperboloidal shell are also calculated.
Research on modern testing technique of optical system resolution based on CCD imaging theory and DLP occurring figure device
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The paper discusses a new method to measure resolution of optical instrument. It is based on DLP technique of photoelectric graph generating automatically, CCD imaging technique and computer image processing technique. It can eliminate the drawback of fatigue easily and artificial effect of visual method. The technique is high precision, high automatic and digital processing.
A method with exact phase-shifting values and its experimental techniques in shadow moiré topography
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According to the characteristic of the optical field arrangement, parallel illumination and parallel receiving in shadow moire method, that the reference grating and the shadow moire can be shifted equal distance at the same time, are proposed in this paper. First, the calculation formula for determining exact phase-shifting values and its experimental techniques were derived. Second, an exact simulation technique in shadow moire topography was constructed on the basis of the conceptions of geometrical interference mode for forming the virtual shadow moire fringes and the calculation formula of exact phase-shifting values. Third, to verify the validity of the calculation principle and simulation technique, the experimental results of the two typical models were offered, one was the cylinder and the other was sphere. These results indicate that the method proposed in this paper can improve the precision of three dimensional shape reconstructions and promote the development of shadow moire topography.
Research on optical fiber minor bend torque telemetering instrument
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This paper analyzed the principle relative twisting angle with optical fibre minor bend, and obtained a theoretical model on torque measurement of the torque. The problem of power supply and signal transmission is the key in the torque measurement of rotating system. The paper applies high-frequency radio influence power to realize radio power supply, applies DSP processing circuit, digital signal transmission circuit, to realize radio signal transmission, using computer for data processing. The application of loop leakage gap antenna array cable as the measuring carrier of rotating signals in the signal blind zone, continue a new best transmission path for the rotating signals. The results of the experiment show the sensor has a very good prospect of application. And it realizes the power monitoring of a rotating device, and pave the way for the automation and intelligence of the devices.
Fringe-locking phenomenon in a laser diode interferometer with optical feedback
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A fringe locking phenomenon in a two beam-laser diode interferometer with strong optical feedback observed in the system is studied in this paper. If a fraction of at least 0.1% of the laser diode output power is returned to it, the fringes are locked even in the presence of the vibrations of an interferometer mirror. The phenomenon is useful for real-time measurement with high accuracy, for it decreasing the measurement error caused by the environment. A theoretical model has been proposed which is based on a four-mirror equivalent Fabry-Porot cavity including the laser cavity and the interferometer. Through theoretical deduction and numerical analysis using the model, the resonant condition of the laser diode was concluded and the dependence of wavelength on the change of the optical path difference of the interferometer calculated, then the fringe locking phenomenon can be well explained. The fringe locking phenomenon is also experimentally studied. It can be observed that when the mirror is driven slowly with a sawtooth wave with a frequency of 100Hz and an amplitude of 1.2μm the fringe locking phenomenon occured. Dependence of the wavelength on the optical path difference is measured too.
Laser ultrasonic technology and its applications in nondestructive testing in solids
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As a new branch of ultrasonics, laser-induced ultrasonics is developed quickly, and has wide applications in many areas recently, for its advantages such as non-contract operation, non-destructive testing, broad bandwidth, high time resolution, high space resolution, no shape limits on samples, etc. Firstly, the principles of the laser-induced ultrasonic generation, e.g., the thermoelastic excitation theory and the ablation excitation theory, were introduced. This paper also described the laser-induced ultrasonic detection by means of the confocal Fabry-Perot interferometer (CFPI). And then its applications in non-destructive testing in solids were introduced in detail. Based on the principles of the laser-induced ultrasonic generation and detection, the structure of the laser ultrasonic detection system was presented. From the velocities of compress wave and surface wave measured by the detection system, elastic constants of aluminium were worked out. The experimental results were in good accordance with the theoretical predictions, which demonstrated that laser ultrasonic technique is practical, reliable and effective. Future prospects for such technology were pointed out finally.
Achromatizing in development of hyperspectral imager
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Because of the fact that the index of refraction varies as a function of the wavelength, the positions of focal planes of various wavelengths also vary with wavelength, which will affect the resolving power of the hyperspectral imager. Based on the image principle of pushbroom hyperspectral imager, the method of tilting image plane was adopted after having tested and analyzed the positions of focal planes of these monochromatic lights. It can reduce the effects of chromatic aberration of the imager’s optical system, and make the imager accord with the request of the resolving power. Then, the effects on performance were discussed.
The system on positioning detecting plasma fluorescence spectrum in reaction chamber
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The real-time detection of plasma fluorescence spectrum in reaction chamber is significant for optimizing running parameters of the plasma syntonization enhanced system and finding sample reaction state. This paper present the new type detection system of fluorescence spectrum. This system applies a principle of control light beam transmitting by entrance pupil and viewing field, and rotated method of optical tube. It can monitor fluorescence spectrum of pointed position in reaction chamber. Some designed essentials about plan of detection range, position optical path and optical path of detecting plasma fluorescence spectrum in the system are introduced in detail. The system features are that it can aim at pointed positions of big luminophor and measure spectrum. It especially suit to real-time detect for plasma states in range nearly substrate holder. This system can applied in PECVD and some research as Chemiluminescence reaction chamber.
Research of the beam steering theory in isotropic acousto-optic device
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In this paper the beam steering theory in isotropic acousto-optic (AO) device is studied. In the process to design an AO deflector, it is important that the device has wider 3db Bragg bandwidth and uniform diffraction efficiency in frequency band. According to the theory about isotropic AO interaction, we can obtain wider 3db bandwidth by using technology of ultrasonic beam steering. It means, the momentum match condition can be satisfied at two track frequencies. The author gains the optimum track frequencies for various numbers of transducer pieces in plane and step configurations respectively. Based upon this argument, farther on, the optimum design parameter of the isotropic AO deflector is also shown up.
The modeling of portable 3D vision coordinate measuring system
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The portable three-dimensional vision coordinate measuring system, which consists of a light pen, a CCD camera and a laptop computer, can be widely applied in most coordinate measuring fields especially on the industrial spots. On the light pen there are at least three point-shaped light sources (LEDs) acting as the measured control characteristic points and a touch trigger probe with a spherical stylus which is used to contact the point to be measured. The most important character of this system is that three light sources and the probe stylus are aligned in one line with known positions. In building and studying this measuring system, how to construct the system’s mathematical model is the most key problem called perspective of three-collinear-points problem, which is a particular case of perspective of three-points problem (P3P). On the basis of P3P and spatial analytical geometry theory, the system’s mathematical model is established in this paper. What’s more, it is verified that perspective of three-collinear-points problem has a unique solution. And the analytical equations of the measured point’s coordinates are derived by using the system’s mathematical model and the restrict condition that three light sources and the probe stylus are aligned in one line. Finally, the effectiveness of the mathematical model is confirmed by experiments.
Research on novel beam homogenizer for excimer laser and evaluating norm of beam uniformity
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A novel trapezoid prism homogenizer is used to improve the uniformity of output energy density of excimer laser. The principle and the design requirements of the novel trapezoid prism are analyzed theoretically, and the optimal position of uniform section is calculated. Using this novel homogenizer, the fluctuation of beam uniformity of XeCl excimer laser is less than 4%. The result is better than that obtained from a normal prism homogenizer. The evaluating norms of excimer laser beam uniformity are analyzed in detail. The process window defines uniformity requirements of excimer laser, while the energy fraction answers the problem of useful percentage of energy within a giving process window. The top-hat factor defines the uniformity in the whole energy range, and the dynamic range is the variation range of screen-homogenizer in the specific application. Using this evaluating norm the uniform beam obtained by the novel trapezoid prism homogenizer is analyzed.
Noncontact thickness measurement of metal foil by means of differential white light interferometry
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A new differential white light interference technique for the thickness measurement of metal foil is presented. In this work, the differential white light system consists of two Michelson Interferometers (MI) in tandem, of which reflective surfaces measured are corresponding surfaces of metal foil. Therefore, the measured result only relates to the thickness but not to the position of metal foil. The method is non-contact, non-destructive, has advantage of high accuracy, fast detection and compact structure. Theoretical analysis and preliminary experimental results have shown that the technique can measure the thickness of foil in the range of 1 μm to 80 μm with satisfactory accuracy and repeatability.
A new model with the active-lap
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The active-lap optical manufacturing technology under computer control has many advantages in fabrication of large aspheric surface. As the lap is translated across the rotating workpiece, the lap's horizontal speed and rotation rate and the total force on the lap to the lap are dynamically controlled to reduce the residual surface error. In order to get the better convergence of the error, the material removal rate (MRR) and a new compositive strategy of lapping with the active-lap are presented. The compositive model is based on not only Preston's relation but also an adaptive fuzzy-neural algorithm, in which the adaptive part is developed to compensate the linear part through learning the feedback on the lapping process. The computer simulation and examination of lapping show good evidence of the effects of the fuzzy-neural model.
Theoretical model of the modulation transfer function for fiber optic taper
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Fiber optic taper has been used more and more widely as a relay optical component in the integrated taper assembly image intensified sensors for military and medical imaging application. In this paper, the transmission characteristic of energy in the taper is analyzed, and following the generalized definition of the modulation transfer function for sampled imaging system, a spatial averaged impulse response and a corresponding MTF component that are inherent in the sampling process of taper are deduced, and the mathematical model for evaluating the modulation transfer function of fiber optic taper is built. Finally, the dynamic and static modulation transfer function curves simulated by computer have been exhibited.
Holographic optical elements for correction of aberrated telescope primary mirrors
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In modern space optical technology, the requirements for telescope systems have been improved and the systems should have diffraction-limited performance and high resolution. As the aperture diameter is increased, some new technologies need to be applied to correct the large aberrations, reduce the weight of the composites and then to minimize the construction and launch costs. The holographic technique for correcting large aberrations of an inferior quality telescope primary mirror is an attractive approach for this purpose and has been investigated in these years. In this paper, the theory of this method is described and some applications are discussed. A holographically corrected telescope system is designed for further experiments. With this system, the performance of the telescope is prospected to near diffraction-limited. And this kind of holographic optical elements (HOEs) acting as holographic correctors should be useful for making low cost, inferior quality primary mirrors as high quality ones in telescopes.
The position relationship in multi-interferograms
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In the high accuracy absolute interferometry, several interferograms from different objects has to be calculated. This paper introduces a technique that ensures the spatial positions of the interferograms coinciding correctly (spatial unity). In this technique the characteristic parameters of interferograms’ position are picked up in the sample matrix coordinates system. And all these characteristic parameters are compared and fed back to the operator. Then the operator aligns the optical path precisely until it achieves the conditions for the absolute measurement. Computer guards the whole process, so the results are more reliability. The absolute measurement of cylindrical surface using this method has been realized and high-accuracy results are obtained.
Interferometric pattern defects recognized by using wavelet transform with DSP
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This paper presents a DSP-base defect recognition system by using wavelet transform and the gray level co-occurrence matrix (GLCM). It can be used to detect the texture image of wafer surface which is captured from a laser interferometer. Wavelet analysis associated with the entropy criterion appears to be a good method for recognizing automatically the defects of the interferometric patterns. Three-dimensional plots of the GLCM for various captured
images have been compared and discussed. The parameter of entropy has been calculated from the GLCM and can be used as an indicator for surface flatness.
Optical design and illumination simulation of Fresnel lenses for marine signal lanterns
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Providing marine signal lanterns, Fresnel lens has been adopted to transfer the beam from the lanterns up to 10 nautical miles (18.53 km). The Fresnel lens with diameters of 250 mm was designed by a ray tracing program and optimized by adjusting the groove parameters of the lens. Each optical sag element which is a part of a lens was independently designed by using the analytical method. The angular luminous intensity distributions (ALID) of this lens were calculated by the illumination analysis program considering the ALID of a light bulb. The ALID of a C-8 type bulb (24 W) was measured with a goniophotometer and its luminous flux was measured by an integrating sphere to be 397 lm. At the best alignment of the bulb, the maximum luminous intensity of the lantern was more than 1000 cd for the 250 mm lens. The ALID was investigated as a function of distance from the lens focus to determine the tolerance margin of the alignment. Horizontal deviations of the light bulb from the focus along the optical axis widened the angular FWHM of the vertical ALID. However, vertical deviations caused shifts of the vertical ALID without spreading the angular FWHM. The designed 250 mm aspherical lens of marine signal lantern was made by the injection molding with single peace acryl. We measured the luminous intensity distribution of acryl lens and found that the MLI of the lens was 827 cd. And the full width at half maximum of the diverging angle of the diverging beam was 3.5 deg. Although the measured MLI was 83% of the calculated result, it would be increased with surface polishing of prototype molding pattern.
Optical test of aspheric elements using instantaneous wedge plate phase shifting lateral shearing interferometer
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In the optical testing of aspheric lenses, the phase shifting lateral shearing interferometer has attracted considerable attention because of its advantage in alignment work. And many phase shifting lateral shearing interferometers were developed. But all of them are time delayed methods which have the time lag between the measurements. When air turbulence and vibration is present, this time lag can be onerous error sources. If we measure all the required interferograms for the phase shifting method at the same time, there should be no time leg. We present a simple instantaneous phase shifting lateral shearing interferometer using a wedge plate and two identical transmission gratings and reconstruct the wavefront error of measured instantaneous phase shifting lateral shearing interferograms.
Study on measurement method of necking process
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In this paper, a new method of optical scanning measurement was put forward, using the semiconductor laser and octagon prism. This method realized on-line non-touch measurement of the necking value and necking position in the process of material tensile testing by the assist of machine scanning. The principle and key technical of this measuring method had been introduced, and the main factor to the measurement accuracy was analysed too. It is shown by test that this method is more accurate, faster and simpler than ever before for giving out the capability of material by omnipotence tensile machine.
Influence of edge error on MTF
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Using a knife-edge to measure the MTF of optical system is a basic way, the paper discuss the influence of slit edge error on MTF by building a mathematical model. The quantitative analysis result was given that it can reach the given precision by only measuring limited area. The qualitative analysis result was also given that fitting-curve-method is better than averaging method for precision.
Optical testing and evaluating system for optical radiation safety for ophthalmic instruments
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In order to evaluate if an ophthalmic instrument has exempt status it shall not exceed any of the emission limits, we designed a relatively simple and inexpensive optical radiation measurement system that can be used to evaluate if an ophthalmic instrument is below the emission limits specified in the standard. The system can complete one measure of the spectral irradiance [in W/(cm*cm*nm)] from 250nm~1100nm in shortest time of 10us and the system is applicable to the instruments with continuous visible light output and pulsed light output.
Estimating static performance parameters of thermal imaging system based on image quality evaluation
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Thermal imaging system is a kind of equipment that is widely used, its static performance parameters are always measured in library. The paper comes up with a new method to estimate the static performance parameters based on image quality evaluation, which can more easily and more quickly to compare performance of two instruments.
Simulation by Monte Carlo method of effect of lidar’s fields of view to echo signals
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The transportation of lidar’s laser beam in seawater is simulated by Monte Carlo method, which combined with statistic, estimate method and weigh method. It should be hypothesized that the incidence laser beam is vertical down and the beam is infinitude thin and vertical. The edge of atmosphere and seawater is located as cone. The axial line of the cone is same to the axial line of the laser impulse spread. It shows that the FOV (fields of view) of lidar’s detector have some influence to the waveform of echo signals. The influence is quite clear when the fields of view is quite small. The larger of the fields of view is, the slower the attenuation speed is. The trend goes to saturation when the fields of view add to a certainty. The conclusion is that the best receiving FOV is between 50mrad ~ 70mrad to the on-board lidar system which located in height at about 500 meters.
Glass optimization using neural network
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The possibility of using neural network to handle discrete variables (glass materials) in lens design is investigated. First, a two-dimensional neuron array is established, in which the minimum of the network energy function corresponds to a design result with controlled chromatic aberrations, acceptable monochromatic aberrations and with a proper combination of selected real glasses. The values of connection matrix and the bias currents are then calculated by means of ray tracing. They are applied to update the neuron asynchronously and randomly, until the valid solutions are achieved. 21 recommended Chinese optical glasses are selected to form a small catalog for the neural network model to reduce the number of the neurons and increase the convergence rate of optimization. A test program is developed using the Macro-PLUS language in CODE V and a double Gauss camera lens is successfully optimized with the model.
Maintenance-free principles of FTIR gas analyzers
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Fourier Transform Infrared gas analyzers have been widely used for speedy quantitative analyses of gases, and it is found that in many cases field maintainability determines the instruments’ online applicability instead of the instrument’s accuracy as is desired. To be maintenance-free is both the target of online instruments and the key to their field applications. Analyses show that if a background can be collected simultaneously with the sample spectrum, the transmittance will be only a function of concentration. Gas spectra collected on Nicolet670 of attenuated inputs and adjusted gains are examined via OMNIC software. Collected data exhibit that the absorbance spectra keep constant when input energy increases 8 times and the instrument gains becomes to 2.0 and 4.0 times. On viewing the absorption peaks vary with wavenumber in high “frequency” and that of the spectrometer itself in low frequency, by subtracting its instrumental response function of a transmittance spectrum extracted by wavelet transform, an absorbance spectrum of air is obtained and comparisons demonstrate that it is a summation of absorbance of the sample and that of gases in the optical path of the spectrometer. Calibration-free and background-free principles are thus exhibited and they construct maintenance-free principles of FTIR gas analyzers.
Imaging quality analysis of KBA x-ray microscope working at grazing incidence
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In the latest 20 years, x-ray imaging technology has developed fast in order to meet the need of x-ray photo-etching, spatial exploration technology, high-energy physics, procedure diagnosis of inertial confinement fusion (ICF) et al. Since refractive index of materials in the x-ray region is lower than 1, and x-ray is strongly absorbed by materials, it is very difficult to image objects in the x-ray region. Conventional imaging methods are hardly suitable to x-ray range. In general, grazing reflective imaging and coding aperture imaging methods have been adopted more and more. In this paper, according to user’s requirement, we have designed a non-coaxial grazing KBA microscope. The microscope consists of two sets of perpendicular spherical mirrors, each set includes two parallel mirrors. Taking it as an example, we have compiled an optical computing program for the non-coaxial grazing imaging systems so as to analyze and evaluate aberrations of KBA microscope. Thus it can help us to get an optimal comprehension of KBA x-ray imaging system. In the same time, the analytical results provide reliable foundation for evaluating imaging quality of KBA microscope.
Measurement on a parabolic surface by quantitative shadow method in computer-controlled optical surfacing
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A new model developing knife-edge test to a quantified method is built in this paper. Based on knife-edge test and image-processing technology, the local surface deformations on aspheric surface can be characterized. The image-receiver CCD (756x504) can assure that the deformation on the little curved face can be measured and detected sensitively. For reducing the influence of the vibration of optical and image-receiving subsystems and offset of images, the least-squares procedure has been used to process images for three times. Then all of the images will be cut at the least-squares circles and moved to the same position, so every pixel on all images can be matched without any offset. In addition, the authors checked the validity of new method by measuring the characterization of parabolic surface under manufactured in our laboratory, and by processing data with simulation method on computer. The result of experiment and calculation can both approve that the least squares techniques is effective.
Image evaluation for optical synthetic aperture imaging system
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In this paper, the theory of optical synthetic aperture imaging system is described, with emphasis on the image evaluation by the Point Spread Function (PSF) and Optical Transfer Function (OTF). The optical synthetic aperture imaging technique achieves higher resolution at the cost of decreasing of Modulation Transfer Function (MTF) in near mid-band regions, and of increasing the sidelobes of the PSF. The image evaluation methods for optical synthetic aperture imaging system are given, such as two-point resolution criterion and MTF. The disadvantage of evaluation methods is analyzed by Rayleigh criterion, Sparrow criterion and threshold criterion. The conclusion is that the imaging quality of synthetic aperture system is no better than that of the single sub-aperture system when the sidelobe is 0.5 times of the central lobe of the PSF. Finally, we propose new evaluation criterions, such as the efficiency factor and quality factor, which are directly linked to MTF.
The tolerance analysis of wide-angle lens
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A paper design is the design, which has the theoretical design only and without considering the manufacturing errors. Therefore, the final performance of the lens assembly might degrade far apart from the paper design. An example of wide-angle lens tolerance analysis is presented. The numerical and graphical aberration degradation analysis shows the useful method to decide the individual lens element manufacturing tolerance.
Color-sensitive characteristics of light source
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According to the chromatic theory, the color sensitive characteristic of light source are studied in the widely used CIE1976L*a*b* color space and color difference. The mathematics formulae of characteristic are deduced. The color sensitive characteristics of D65 and A light source are studied. The general laws of the color sensitive characteristic are concluded. The mathematics models of light source can be used in some fields such as making light source.
Annular subaperture interferometric testing technique for large aspheric surfaces
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A new method to test large aspheric surface by using Annular Sub-aperture Interferometric Testing (ASIT) is described in this paper. It solves the two main difficulties, which are manufacture difficulty and high cost of auxiliary elements (optics compensator, CGH, large reflector) used generally in testing the large aspheric mirror. The method reduces departure between the reference wavefront and tested wavefront to the measurement range of the interferometer by testing annular subaperture of aspheric surface, which makes reference wavefronts with different curvature radius match corresponding annular subaperture, then sews all sub-aperture datum together with a suitable algorithm to get the whole information of the surface. A stitching mathematics model is provided. The feasibility of the technique has been demonstrated by comparing test results from an autocollimation test and ASIT of an 152-mm diameter paraboloidal mirror. This method extends the dynamic range of interferometric measurements, by which the large, fast aspheric surface can be directly tested without additional optical elements.
Research and application of virtual reality in optical measurement & control system
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This paper introduces the new technology -- X3D (Extensible 3D specification) into optical measurement and control system. And a prototype system is presented, the results of the experiment are given and analyzed. This system can simulate the polishing process well and improve the manufacturing efficacy and quality.
The three-dimensional focusing behaviors of compound x-ray lenses
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A theoretical method for evaluating the three-dimensional focusing performances of the compound x-rays lenses is presented in the present paper. The relationship between the transverse and axial focusing behaviors is considered and a simple calculation that predicts the transverse and axial focusing behaviors of the compound x-ray lenses is also presented. As an example, the three-dimensional focusing performance of a compound x-ray lens with Al material is predicted. The dependences of the three-dimensional focusing performances on the compound lenses’ structural parameters are observed for the Al compound x-ray lens. Moreover, the approximate tolerances in the setting of the receiving planes are also considered for x-rays of 4.95keV, 14.99keV and 29.78keV.
Modulation transfer function evaluation of charge-coupled-device camera system based on liquid-crystal display random targets
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In order to overcome the sampling-scene phase effect in the modulation transfer function (MTF) measurement of sampled imaging systems, a method using a pseudorandom number generating algorithm to generate several random targets displayed on a liquid-crystal-display (LCD) graph generator to evaluate the MTF of charge-coupled device (CCD) in visible region is discussed. The major advantages of this technique are that it has been demonstrated as a shift-invariant method without requiring mechanical scanning, and it is easy to generate a large number of random targets on LCD by computer program to get the average result and reduce measurement noise. By experiments, this technique has got a reliable MTF result and agrees with the usual methods. This method is expected to be used to develop a real-time video MTF testing software system.
ANN-based calibration model of FTIR used in transformer online monitoring
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Recently, chromatography column and gas sensor have been used in online monitoring device of dissolved gases in transformer oil. But some disadvantages still exist in these devices: consumption of carrier gas, requirement of calibration, etc. Since FTIR has high accuracy, consume no carrier gas and require no calibration, the researcher studied the application of FTIR in such monitoring device. Experiments of “Flow gas method” were designed, and spectrum of mixture composed of different gases was collected with A BOMEM MB104 FTIR Spectrometer. A key question in the application of FTIR is that: the absorbance spectrum of 3 fault key gases, including C2H4, CH4 and C2H6, are overlapped seriously at 2700~3400cm-1. Because Absorbance Law is no longer appropriate, a nonlinear calibration model based on BP ANN was setup to in the quantitative analysis. The height absorbance of C2H4, CH4 and C2H6 were adopted as quantitative feature, and all the data were normalized before training the ANN. Computing results show that the calibration model can effectively eliminate the cross disturbance to measurement.
Data-processing method of white-light differential interference based on wavelet transform
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A thickness measurement system of ultra-thin metal foils using differential white light interference has been investigated, where a data processing scheme, using wavelet transform has been carried out. The analysis of simulation result indicates that this method has high accuracy and can be applied in the course of actual measurement.