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Proceedings Volume 0661

Optical Testing and Metrology

Chander Prakash Grover
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Proceedings Volume 0661

Optical Testing and Metrology

Chander Prakash Grover
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Volume Details

Date Published: 25 November 1986
Contents: 1 Sessions, 63 Papers, 0 Presentations
Conference: 1986 Quebec Symposium 1986
Volume Number: 0661

Table of Contents

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Table of Contents

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Optical Processing And Holography With Incoherent Light
E. N. Leith, D. Angell, S. Leon, et al.
Several applications of incoherent optical processing and holography are discussed, including spatial filtering, tomography, resolution beyond the classical limit, and holographic optical elements.
Application Of White-Light Processing To Interferometric Studies
F. T. S. Yu, S. Jutamulia
One of the interesting applications of white-light optical signal processing must be psuedocolor encoding. In this paper, we will demonstrate some of those applications to holographic interferometric and metrological studies. Techniques of producing pseudocolor encoded holographic fringe patterns and misfocused speckle interferograms are provided. These techniques allow the viewing of a multiset of encoded interferograms simultaneously. Talbot interferometric technique for pseudocolor encoding phase object and depth utilizing a white-light processor is also presented. The white-light optical processing technique offers the simplicity, versatility, and cost effectiveness in the application to interferometric and metrological studies.
Observation Of Difference Displacement Fringes Using Comparative Holography And Its Application To The Detection Of Concealed Flaws
Pramod K. Rastogi
Comparative holography is an important development in laser based metrology. The technique provides holographic interferometry with the ability to optically subtract the phase terms to obtain a fringe pattern corresponding to the difference in deformations of two nominally identical specimens. After laying a theoretical foundation to the technique, the paper evokes a couple of practical configurations to implement the technique. The method is experimentally demonstrated and results obtained in application to flaw detection are presented. Finally, a few considerations into the formation of the difference displacement fringes are briefly stated.
Holographic NDT On Pipes: Predicted Fringe Patterns And Experimental Results
David L. Mader
Holography has been used in the electric utility industry in practical tests for deformation of pipes subjected to repair procedures. In research studies, the use of holography for measurement and NDT (nondestructive testing) has been explored for pipes. The expected interferograms have been simulated with a mathematical model which embodies elastic deformation as well as rigid body motion. Experimental verification of the model shows that it may be used for software compensation of rigid body motion, and for measurement of bending, torsion, pressure, and thermal expansion.
Statistical Analysis Of Holographic Fringe Formation And Localization
F. P. Chiang, Q. B. Li
Holographic fringe formation and localization are studied using statistical optics in terms of speckle movement and average speckle size. The concept is useful in the application of holospeckle interferometry studies such as three dimensional crack tip deformation measurement.
Generalized Far-Field Holography At Non-Image Planes
C. S. Vikram, M. L. Billet
The imaging process of far-field holography with reconstructions at non-image planes is described in detail. The recording and readout source points are assumed to he generally anywhere on the optical axis and their wavelengths are also considered to be different. The emphasis is given to the diffraction pattern for the analysis of size and position of small particles, bubbles, etc. The case of two-dimensional object cross-sections is discussed in detail.
Image Reconstruction Techniques For Computed Tomography From Sparse Data: X-Ray Imaging On The Varennes Tokamak And Other Applications.
R. Decoste, P. Noel
Computer assisted tomography will be used on the Varennes tokamak, a medium size thermonuclear fusion research device, to reconstruct 2-D images of the X-ray emission from the plasma. Five full views or projections of the plasma with 16 detectors each will be available with a temporal resolution of a few microseconds. The X-ray imaging system and the reconstruction technique must take advantage of any prior knowledge of the object or plasma since the viewing access is quite limited and the data available is sparse. Comparative simulated examples demonstrate the advantages of Fourier harmonic expansion reconstructions over two other popular techniques. An example of possible industrial applications involving gross detection of material defects and local density variations is also discussed.
Utilisation Of Vector Nature Of Light In Imagery And Image Processing
A. K. Chakraborty, Ajay Ghosh
Although polarisation properties of light waves have recently been utilised for a number of image processing applications, many aspects of vector nature of light relevant to the imagery problems have still remained unexplored. In the present article, we have studied the effects of polarisation masks of different nature on the lens aperture on the imaging characteristics of the lens. The imaging characteristics of a birefringent lens have also been reported. The study reveals that the imaging systems using such polarisation devices will lend an additional dimension to the optical image processing and will yield results unachievable with scalar waves. The possible applications of the imaging systems making use of polarising devices have been indicated.
Deformation Measurements At Very High Temperatures By ESPI And Moire Methods
Ole J. Lokberg, Jan T. Malmo
We describe two optical methods which have been used to measure the deformation and general behaviour of objects heated to high temperatures. TV-holography or ESPI has proven capable to follow and measure the surface behaviour and deformation with interferometric sensitivity to temperatures about +1600 °C, where the temperature limit is mainly determined by practical experimental problems and is not of fundamental character. Some preliminary results will be presented. The Moire method can be used to measure in-plane object movements to temperatures so far up to about +1300 °C by recording the variation in emissivity of an inscribed surface grating without external illumination.
Common Path Interferometer Using Optically Induced Molecular Reorientation In Liquid Crystals
C. P. Grover
Optically induced molecular reorientation in nematic liquid crystals has been used to obtain a common path interferometer for measuring aberrations of the incident beam. When a strong laser beam is focussed onto homeotropically aligned liquid crystals, it produces above a threshold value, a molecular distortion, the profile of which depends upon the point spread function of the incident beam. The strong zero spatial frequency component creates a highly distorted centre due to the crystal birefringence producing a diverging spherical reference wavefront. This interferes with the directly transmitted aberrated wavefront producing fringes in the same way as in the point-diffraction interferometer. This interference phenomenon occurs in the extraordinary wave and resulting fringes represent directly the thickness contours of the incident wave.
A Phase Measuring Radial Shear Interferometer For Measuring The Wavefronts Of Compact Disc Laser Pickups
Bruce E. Truax
A phase measuring radial shear interferometer has been developed that enables the user to measure the wavefront of Compact Disc or other optical storage laser pickups. The instrument is designed to operate over the wavelength range from 700nm to 830nm. It will accept the diverging wavefront of any optical storage laser pickup, and it includes a holder for the thin coverplate necessary to compensate for the plastic or glass overcoat on the optical storage media. The interferometer is equal path and has been achromatized over the wavelength range so that the source coherence length can be less than one millimeter. Compensation for variations in light source intensity is accomplished by a rotating variable neutral density disk driven by a servo system. This compensation system permits input light levels to vary from 0.1mw to as great as 100mw. Data processing options include: peak-to-valley and root-mean-square wavefront distortion computation with isometric and contour plotting as well as Zernike polynomials, point spread function, and modulation transfer function. System accuracy depends on the numerical aperture of the input source. With the standard collimating optics the input numerical aperture can be as large as 0.65. For this numerical aperture the instrument is typically better than 1/5 wave at 780nm. For 0.5 numerical aperture (typical for most Compact Disc pickups) the system performance is better than 1/10 wave. If more accurate measurements are required, the wavefront of the instrument must be stored and subtracted from the measurement of the pickup. Results of measurements of Compact Disc heads will be presented and other applications of the instrument will be discussed.
Photometric Ordering Of Ordinary Moire Fringes
James R. Pekelsky, Ding Xinhong
A method is described for ordering the fringes in ordinary moire topograms that resolves hill-or-valley ambiguities. A photometric model is used to predict the expected surface brightness for the up and down surface orientation possibilities. Only one of the orientations produces estimates that are consistent with the measured values. The photometric model is based globally upon the moire geometry, and locally upon the surface reflectance properties. Topograms of test objects and human subjects are presented to illustrate the principle of photometric ordering.
Automatic Alignment Technique For X-Ray Lithography Using Moire Signals In Reflection
Yoshiyuki Uchida, Masato Furukawa, Kazuhiro Hane, et al.
This paper deals with an automatic and precise alignment technique between a wafer and a mask in X-ray lithography, using two pairs of moire gratings, one on the wafer and another on the mask in each pair. The moire signals are detected in zeroth order beams in reflection. These two moire optical signals are converted to digital signals by A/D converters, and then the digital signals input to a microcomputer. The microcomputer controls the alignment of X stage through a stepping motor, using the difference between these two digitalized moire signals. The precision of the present system is resulted from the pitch of the gratings as an error signal, the relative displacement between the gratings per step of the stepping motor, the resolution of the A/D converters and S/N of the system. The response time of alignment is determined by the response time of the feed back loop. Experiments were carried out by using a grating of 25 μm pitch. The minimum displacement corresponding to one step of the stepping motor was 14 nm. The resolution of the A/D converters was 12 bits and the response time was 1.2 s. With these parameters a control reproducibility better than 50 nm was obtained. Improvement in the control precision by an order of magnitude is expected by using a pair of quadruple gratings, a combined unit of 4 matched photodiode and PZT controllers. The design considerations of a suitable X-ray lithographic mask alignment system are given.
Development Of Double Twin Path Laser Interferometer For Thin Film Thickness Measurement
Yoshiyuki Uchida, Motomu Asano, Masatoshi Kuwata, et al.
We describe a novel laser interferometer which measure thin film thickness automatically with simultaneous reference level control. The system use a He-Ne laser as light source and a grating as beam splitter-recombiner. The 0 and -1 order beam diffracted by the grating are reflected at the substrate and the +1 order beam is reflected at the film. These beams again pass through the grating and diffracted to interfere. The interference between the diffracted components of 0 and -1 order beam is used to control the reference level, and the interference between the diffracted components of 0 and +1 order beam is used to measure the film thickness. Rising in the two pairs of twin path we call this interferometer as a double twin path laser interferometer. Theoretical estimations give the high accuracy of better than ±0.1 nm. A mechanically stable and compact system has been constructed. The experimental results show that the performance of system is fairly satisfactory. Alminium films of thickness ranging from 70 nm to 300 nm were measured with a accuracy of ±20 nm. Additionally we discuss the problems in the first trial construction and how to improve the accuracy and stability in this system. The second trial construction including the improvements is attempted.
Comparison Of Harmonic Weighting, Fitting, And Crossing Points For Locating Optical Interference Fringes
William Primak
The problem in precisely locating a fringe in an interference pattern is that the light intensity varies so gradually in the regions of the maxima and minima. Such devices as logarithmic weighting and half-shades have been used in the past. Here, the methods of fitting the fringe intensity profile, harmonic weighting (which converts the fringe profile into a sawtooth), and using the mid-intensity crossing points (where the intensity varies most steeply) are compared, and their precisions in the presence of statistical errors are described. The implications for practical measurement are discussed.
Optimal Removal Of All Mislocation Effects In Interferometric Tests.
Eric W. Young
A technique is presented for calculating the aberrations induced by mislocation of a large aspheric optic in an interferometric test. This mislocation can be described by a set of five vectors representing small displacements from an ideal position relative to the interferometer. Two different interferometric test configurations will be analyzed. In one such configuration, the optic is tested in autocollimation at its focal point. In the second such configuration, the optic is tested in retroreflection at its center of curvature. The appropriate aberration function for a displaced but otherwise perfect conic section is developed for each configuration. For testing at focus, this function depends on all five degrees of freedom, but four of them couple in pairs. For center-of-curvature testing, the aberration function depends on translational displacements only, not tilts. We show that even when tight mechanical tolerances are applied to positioning, the aberration effects can still be significant for high precision work. We carry out detailed computations for two optics of typical dimensions to illustrate the importance of these effects. We present a technique to optimally remove errors associated with displacement of an otherwise perfect conic section. The method developed is completely general, including all relevant degrees of freedom. Indeed, the least-squares analysis is carried out on a loss function whose form is independent of testing method and conic constant. Once these mislocation-related errors have been removed, the metrologist can calculate the true aberration function of the optic under test. In this fashion, surface correction contours can be generated for further material removal if required.
Phase Shifting Interferometry Using Polarization Component Phase Shifters
J. Giroux, M. P. Kothiyal, C. Delisle
The use of polarization components as phase shifters in phase shifting interferometry has been investigated. Results of an error analysis carried out to determine the influence of the errors of the polarization components on the measured value of phase are presented. Cyclic shear interferometer with polarization phase shifting is used for phase shifting interferometry.
Infrared Interferometers At 10 µm
Jacques Lewandowski, Bernard Mongeau, Maurice Cormier, et al.
The two infrared (10µm) wavefronts of an interferometer (Michelson or Mach-Zehnder) interfere separately with a tilted reference beam on a dynamic recording medium consisting of a thin oil film on a glass substrate. Illumination of this twin hologram with a visible (HeNe) beam reconstructs simultaneously, in the same direction, two wavefronts characteristic of each arm of the interferometer. Practical realization and experimental constraints, such as air turbulence and mechanical vibrations, are easily satisfied with these long-wave-length interferometers. Experimental results include air wedge determination, homogeneity test of a NaCl plate, step deposit evaluation and afocal assembly analysis. The real-time aspect of our recording medium also permits the visual observation of transient phenomena.
Fundamentals And Overview Of Fiberoptic Sensors
Shaoul Ezekiel
Fiberoptic sensors offer a number of unique features which make them attractive for a variety of applications. For example, a fiberoptic sensor can be immune to electromagnetic interference, is non-electrical, is compatible with fiber telemetry, can be very sensitive as well as being small in size and weight, and may be used in the development of sensor arrays. Fiber sensors have been considered for the measurement of a large number of physical parameters, ranging anywhere from temperature and pressure to rotation rate, magnetic field, specie concentration and, even, nuclear radiation. The fields of application of fiberoptic sensors include navigation, robotics, undersea detection, medical, chemical and so on.
Overview Of Advanced Components For Fiber Optic Systems
Ramon P. DePaula, David W. Stowe
The full potential of low-loss optical fibers will not be realized until compatible high-performance components are available at low cost. In this paper we consider a few of the advanced fiber components which have been demonstrated in the laboratory or, in some cases, are available commercially. Areas requiring further development are also noted.
Time Domain Referencing In Intensity Modulation Fiber Optic Sensing Systems
Grigory Adamovsky
Intensity modulation sensors are classified depending on the way in which the reference and signal channels are separated: in space, wavelength (frequency), or time demains. To implement the time domain referencing different types of fiber optic (F0) loops have been used. A pulse of short duration sent into the loop results in a series of pulses of different amplitudes. The information about the measured parameter is retrieved from the relative amplitudes of pulses in the same train.
Electronics For A Closed Loop Fiber Optic Gyroscope
K. Jew, B. Bednarz, J. A. Dankowych, et al.
This paper describes the electronics subsystem of a transportable demonstration closed loop fiber optic gyroscope. A detailed description is given of the in-house-built circuits such as the photodetector amplifier, phase sensitive detector, dither generator, high speed 32-bit counter and the single board computer interface for data acquisition and control. A sample gyro drift run is presented.
A Laser Feedback Control Design For Passive Ring Laser Gyros In A Very High Finesse Cavity
Mark A. Lorenz, Gerald L. Shaw, Daniel J. Biezad
High finesse resonant cavities proposed for use in large passive resonant ring laser gyroscopes exhibit linewidths significantly narrower than commercially available frequency stablized lasers. For PRRLG applications, this can limit the performance due to the decreased signal-to-noise ratio. In this paper, a unique design for a PRRLG is presented, whereby the linewidth of a He-Ne laser is narrowed by frequency locking the laser to a 25,000 finesse, 169 cm2, resonant cavity. A resulting random error of 0.0078 Earth Rate Units (ERU) was achieved for an averaging time of 10 seconds. Extrapolation of the performance to a much larger PRRLG indicates that desired sensitivities for precision rate sensor testing and general relativity experiments is attainable.
Laser Anemometry - Some Simple Errors
E. J. Fjarlie
Attention is drawn to alignment and operating difficulties for a laser anemometer operating in the fringe mode looking at a filament target. Signal characteristics are sketched and some reasons for the difficulties are outlined.
Interpretation Of SM Fiber OTDR Signatures
M. S. O'Sullivan, R. S. Lowe
Single mode fiber signatures, obtained by OTDR (λ= 1.55μm), are interpreted using the Gaussian field approximation. Fiber loss is separated from mode field diameter (MFD) variation by means of a two-way measurement. OTDR measurements of fiber attenuation distributed MFD variations, splice loss and MFD mismatch at a splice are compared with cutback measurements of the attenuation and variable aperture measurements of MFD. In all cases, OTDR and the standard techniques are in good agreement, namely: ±0.01 dB/km for attenuation, ±0.08μm for distributed MFD variations, ±7% for splice loss and ±.16μm for MFD mismatch.
1.3 µm All-fiber Passive Optical Rotation Sensor
Bruce R. Youmans, Willis C. Goss, Randy K. Bartman, et al.
An all-fiber, 1.3 µm passive optical rotation sensor utilizing 4.2 km of single mode fiber and synchronous detection has been constructed and tested in the laboratory. RMS noise equivalent rotation rates of 0.005 deg/hr have been measured. Drift and scale factor variations resulted in a change in the indicated rotation rate of 0.4 deg/hr over a 1 hour time period.
Fiber Optic Acoustic Sensors
J. A. Bucaro, J. H. Cole, A. Dandridge, et al.
The physical principles which provide the basis for fiber optic acoustic sensors (microphones and hydrophones) are discussed for both interferometric and microbend sensor designs. The response of the interferometric microphone is examined from 1 Hz to 50 kHz. Experimental results for a microbend based microphone for low frequency applications are presented. The acoustic response of optical fibers is discussed in relationship to ultra-sonic probes and fiber modulator applications. Finally, a brief description of the status of low frequency fiber optic hydrophones is presented.
Ocean Applications Of Fibre Optic Sensors
Barry E. Paton
The unique features of fibre optic sensors have sparked wide spread interest in applications that provide new sensor capabilities or offer cost or performance benefits over existing sensors. Fibre optic sensors are small, lightweight, electrically passive and immune to electromagnetic interference, making them attractive for industrial, marine, military and medical applications. The oceans provide a unique arena where many of the attributes of optical sensing can be and are being applied today. However, the oceans also present many challenges in bringing fibre optic sensing to an especially hostile environment.
A Fibre Optic Sensor For Remote Rotation Sensor
Terence M. Dwyer, Barry E. Paton
A fibre optic position sensor is used to enhance the performance of conventional stream flow meters. Non-contact optic detection allows operation in polluted or salt water. In addition, the small size of the optical detector allows a sixteen-fold increase in resolution.
A Fibre Optic Remote Sensing Head For In Situ Chlorophyll-a Fluorescence Measurement In Phytoplankton
J. W. Snow, B. E. Paton, A. Herman
Two standard laboratory fluorometers, the Turner Model III and the Turner Designs Model 10, have been modified for in situ measurement of chlorophyll-a fluorescence in phytoplankton to depths of 100m through an optical remote sensing head, a fibre optic cable assembly, and an external tungsten halogen source. Sensitivities of 0.1 mg/m3 of chlorophyll-a have been achieved which is adequate for most oceanographic work.
Wide Range Optical Fibre Microbending Sensor
Kevin E. Lindsay, Barry E. Paton
Several different coated fibres, representing both the step index and graded index groups, were tested for their sensitivity to bending using a mandrel wrap technique. Different sensor designs indicated that a grooved block arrangement was most suitable. A linear response over a large dynamic range was obtained by pretensioning the fibre in the sensor head.
A Fibre Optic Sensor Of Physiological Parameters
J. P. Legendre, G. V. Forester
This paper presents an ultraminiature fibre optic probe capable of physiological monitoring in situ. The system has been described previously where a fibre optic reflectometer was configured as a temperature sensor and as a refractometer. For the present experiments a bare fibre tip was used as sensing element. We show that we have been able to monitor cyclic physiological parameters such as heart and respiratory rates in various animal preparations. The probe has been used to obtain signals from the oesophagus, the lower gastro-intestinal tract, the abdominal cavity and from blood vessels (arteries and veins). The probe has also measured phasic activity coincident with mechanical activity of isolated heart muscle. The small physical size of the sensor (125 µm diameter), its flexibility and the fact that it is biologically inert are all very important characteristics for medical and biological considerations. Most recently, the probe has been used to monitor cardiac and respiratory rates while obtaining NMR spectra assessing metabolic activity. This was possible only because the probe is magnetically transparent.
Integrated Electro-Optic Modulator For Ultra-High-Frequency Electric Field Sensing
D. Landheer, A. Podgorski, J. Chrostowski, et al.
Integrated optics offers a unique opportunity for ultra-high frequency electric field sensing. We report here design and operating parameters for a Mach-Zehnder travelling-wave modulator for operation at ultra high frequencies. The interferometer is fabricated on LiNb03 crystals by Ti-indiffusion. The electrode design features an asymetric coplanar line coupled to the optical waveguides by a series of thin, parallel capacitor structures.
Alignment And Evaluation Of Integrated Optic Components Using An OTDR
Robert C. Gauthier, Barry E. Paton
An experimental technique is reported for the alignment of integrated optic components with single mode optical fibres using optical-time-dom ain reflectom etry. Fresnel reflections monitored at one end are used in the alignment procedure. An integrated optic polarizer is evaluated to demonstrate the usefulness of this approach.
A Fiber Optic Sensor Sensitive To Normal Pressure And Shear Stress
Frank W. Cuomo, Robert S. Kidwell, Andong Hu
A fiber optic lever sensing technique that can be used to measure normal pressure as well as shear stresses is discussed. This method uses three unequal fibers combining small size and good sensitivity. Static measurements appear to confirm the theoretical models predicted by geometrical optics and dynamic tests performed at frequencies up to 10 kHz indicate a flat response within this frequency range. These sensors are intended for use in a low speed wind tunnel environment.
Optical Metrology In Length And Mechanical Standards
G. D. Chapman
A review is presented of the introduction and development of optical techniques and devices in the broad area of metrology in length and mechanical standards. Emphasis is placed upon those techniques which have been made possible by the use of lasers, or which have substantially increased accuracy and reduced work loads on a routine basis. In particular, the use of optical fourier transform techniques in metrology applied to disciplines as diverse as standards, engineering, plasma physics, and biology are explored.
Some Recent Advances In Speckle Techniques For Photomechanics And Optical Metrology*
F. P. Chiang
Major advances in using coherent and incoherent speckle patterns for displacement and strain measurements are reviewed. Topics include the laws of spatial movement of laser speckle, the halo functions of coherent and incoherent speckle patterns, the factors that result in speckle decorrelation which, in turn, affects the fringe visibility and sets the upper limit of displacement measurement, the new techniques of holospeckle interferometry, real-time and electron microscope speckle photographies and finally the automatic processing of Young's fringes, and digital correlation techniques.
Scattered Light Speckle And Its Application To Interior Strain Measurement
Ye Ying Zhao
By using a "white-light" laser to illuminate a thin sheet of a transparent body seeded with tiny glass beads interior strain fields can be obtained by photographing the speckles before and after deformation via double exposure and subsequent Fourier filtering. Experimental results of interior strains of a block loaded by a ball were obtained and compared to theory with good agreement.
Measuring Small Rotation Rates With A Modified Michelson Interferometer.
Erik Stijns
A Michelson interferometer can be transformed into an angle-measuring instrument by replacing one of the end mirrors by a right-angled prism. We calibrated such a device and found good agreement with the calculated values. Some sources of error are also discussed.
Laser Coordinate Measuring Machine For Cylindrical Parts
Omer L. Hageniers
This paper addresses the design and construction of a Laser Coordinate Measuring Machine (LCMM) for the measurement of cylindrical parts. The primary application area of this system is the measurement of aircraft jet engine spools, hubs, discs and spacers, and its measuring range of 5" to 26" diameter and height to 20" has been chosen to meet the volumetric needs of this particular application area. Overall system accuracy is ± 0.0002" and the average time to measure a typical part is 6-1/2 minutes. Overall system capability is summarized in Table 1.
Standards For Three-Dimensional Mensuration With Electron Micrographs
Sanjib K. Ghosh
Precision measurement in three-dimensions and mapping require acceptable "standards" for the electron microscope (EM) systems. The best available standards are carbon replicas made from master diffraction gratings. Since these are two-dimensional, certain configurations of convergent micrography can be used to "generate" the third dimension. The process, as has been developped with regard to both Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM), is discussed. The procedure can be used in calibrating any EM system, on-the-job, even on an ad hoc basis. Fundamental to the procedure is the collinearity condition inherent in the imaging system ensuring that the object point, the corresponding image point and the center of projection lie on the same straight line. The consideration of the involved parameters and of the necessary number of micrographs in the solution are discussed. Certain very encouraging results obtained from recent research studies at Laval University are presented.
Single-Hologram Method For Evaluating Displacement Field
Marek J. Matczak
The method for evaluating all three independent components of displacement vector at each point of object surface by means of only one double-exposed hologram is presented. The method is based on the fringe-visibility measurement.
Direct Holographic Determination Of The Rotation And Strain Fields By Means Of The Fringe Visibility Method
Marek J. Matczak
The method for direct evaluating the surface-strain tensor field and the tensor or vector field of the surface rotation by means of three different holographic interferograms is proposed. This method is based on the fringe-visibility measurement by using the imaging system with a rotatable slit diaphragm.
Three-Dimensional Surface Metrology Using A Computer Controlled Non-Contact Instrument
James C. Wyant, Keith N. Prettyjohns
This paper describes a non-contact three dimensional surface profiler. The instrument is based upon direct phase measurement interferometry using a microscope to measure surface heights over an area from 0.25 mm square to 4.0 mm square. A 256 X 256 element photodiode detector array is used as the image sensor. Computer software has been written to control the instrument, and perform the phase measurement and full statistical and Fourier analysis of the surface. Results are shown of measurements for a variety of surfaces tested.
Measuring Step Heights Using An Optical Profiler
Katherine Creath
Two-wavelength phase-shifting interferometry is applied to an interference phase-measuring microscope enabling the measurement of step heights. The surface is effectively tested at a synthesized equivalent wavelength λeq = λaλb/|λa - λb| using measurements made at wavelengths λa and λb. The rms repeatabilty of the technique is λ/1000 at the equivalent wavelength. To improve the precision of the data, the phase ambiguities in the single wavelength data are removed using the equivalent wavelength results to determine fringe orders. When this correction is made, a measurement dynamic range (feature height/rms repeatability) of 104 is obtainable. This technique enables features of up to 10 μm in height to be measured with a 10x objective.
Surface Texture Measurement By Computer Vision
Y. J. Chao, C. Lee, M. A. Sutton, et al.
A fully automated, non-contacting, full field method is presented to measure the surface roughness parameters using a computer vision system and image processing techniques. The texture features, namely, coarseness, contrast and roughness are extracted from digitized images of standard surface roughness comparator plates and correlated with the arithmetic average roughness (Ra) of the surface. The vision system offers a fast and accurate method for the on-line automated surface roughness inspection of machined components.
Transmission Grating Incorporated Displacement Sensor: A Critical Study Of The Sensor Parameters
K. Hane, C. P. Grover
The imaging phenomenon due to a rectangular transmission grating has earlier been described in its close vicinity. By reversing the conjugate planes, it has been possible to obtain highly magnified grating images. The phenomenon has been successfully utilized for sensing displacements of the object grating. We have observed the image magnification in the range 102 to 103 by using a 25μm object grating. The optimum imaging conditions have been explained on the basis of the OTF theory. The signal contrast has been studied theoretically and experimentally as a function of the size and polychromaticity of the light source and the distance between the object and pupil gratings. In the case of two rectangular transmission gratings, the signal consists of a triangular wave when the image is observed at infinity under the optimum imaging conditions. As the image plane approaches the pupil grating, the waveform tends to become sinusoidal due to the loss of higher spatial frequencies. We have employed the differential detection method and the sensitivity in the linear region has been estimated to be 0.01μm.
Simultaneous Laser Beam Profiling And Scaling Using Diffraction Edge Waves (DEW)
Pierre Langlois, Roger A. Lessard
A simple method of laser beam profiling using a scanning knife-edge is presented. Instead of monitoring the nonobstructed part of the beam as is usually done, the photo-detector is placed completely outside the beam and measures the light intensity of the DEW. Thus the spatial profile of very small Gaussian beams is obtained directly on an oscilloscope without any inversion procedure. By using the DEW emitted by another beam focused through a grating it is also possible to get a spatial calibration scale.
Long Range Laser Alignment Systems
Dimitri Petrov
Conventional artillery alignment procedures based on survey techniques are time consuming and have become tactically obsolete. An opto-electronic system has been developed which allows an accurate alignment of field guns and self-propelled guns with respect to grid north within a few seconds.
Holographic Determination Of The Surface Shape By Means Of The Fringe Visibility Method
Marek J. Matczak
The method for evaluating the distributions of the radius-vector and the normal of the object surface on the base of the fringe-visibility measurement is presented. This method requires to form an interference image by means of two coherent illuminating waves of the same wavelength which can be used separately - for the holographic double-exposure or real-time technique, or simultaneously - for only one holographic exposure or for direct analysis of the image without holographic recording.
Sphericity Measurements Of Full Spheres Using Subaperture Optical Testing Techniques
Robert D. Day, Thomas A. Beery, George N. Lawrence
This paper discusses the progress being made on the development of applying subaperture interferometric testing techniques to making sphericity measurements on the entire surface of a full sphere.
Image Quality Evaluation For Aerial Lenses
Hartmut Ziemann, Manfred Paulun
The Photogrammetric Research Section of the National Research Council recently completed the development of an apparatus for the determination of optical transfer functions from line spread functions measured for aerial lenses. The paper provides background information relevant to image quality assessment at the National Research Council and reviews results obtained during the testing of the apparatus. It addresses various aspects of the determination of set-up parameters to be used for the measurement of line spread functions and presents results obtained in an effort to check the alignment of critical parts of the apparatus.
An Optical Gun Muzzle Sensor To Improve Firing Accuracy
Raymond Carbonneau, Jacques Dubois, Geoffrey Harris
Thermal deformations of gun/tank components can affect the firing accuracy of modern tanks. To alleviate this problem, an optical gun muzzle sensor has been designed to provide corrections to the computer-generated signals responsible for fire control. This paper first summarizes some typical deformations that induce firing inaccuracies, then reviews various optical approaches to sensing the angular position of a gun and finally, discusses the design of an optical instrument recently developed in Canada for this purpose. The technique involves a laser diode transmitter/receiver mounted on a turret roof and a small mirror at the gun muzzle to reflect the laser beam. Thermal distortions induce a beam deflection which is measured by an analogue, two-axis position sensing detector whose output signals are converted into angular corrections and sent to the fire control computer. The optical design and some specific engineering problem's are thoroughly discussed.
A New Test For Cylindrical Optics
J. Geary, L. Parker
This paper discusses preliminary investigations of a novel interferometric approach in testing cylindrical optics that makes use of an optical fiber as a cylindrical reference surface. Keywords: optical testing; cylindrical optics; fiber optics; interferometry
Design And Characterization Of Graded Reflectivity Mirrors
Nathalie McCarthy, Pierre Lavigne, J.-G. Demers, et al.
A new design of graded reflectivity mirrors is presented. It consists in depositing an appropriately shaped thin layer of a high-refractive-index dielectric on a transparent substrate. The technique used to deposit the profiled layer is discussed. Mirrors with Gaussian reflectivity profiles have been fabricated for use at 10.6 and 3.7 μm. An interferometer which has been setup to characterize the distortions of the reflected and transmitted wave fronts of one of the 10-μm prototypes is described and the results are presented.
Calibration Of Thermal Imagers
Paul Chevrette
This document is an attempt to establish and define the parameters of importance for valid calibrated infrared signature data and to lay down guidelines to be adapted to each individual system in order that exchanged data between laboratories could be made useful and comparable. It is assumed that the data gathering instrument is a thermal imager. The initialization of the calibration parameters characterizing the system is discussed, followed by a description of the field calibration procedures. Then the basic equations for image analysis and conversion to radiometric data are presented for a general and ideal case. Three special cases are considered: the effect of ignoring the atmospheric corrections, the effect of having reference blackbodies at a range different from the target, and the effect of using a system with built-in references.
Experimental Study Of A Liquid Crystal Light Valve As A Component In A Real Time Optical Image Processing System
R. H. Arsenault, V. M. Ristic, A. Yi, et al.
The liquid crystal light valve (LCLV) developed by Hughes is a real time optical to optical image transducer capable of accepting a low-level input light intensity distribution and transforming it into an output light amplitude distribution. The input and output beams are completely separate and non-interacting. This paper describes the measurements and analyses undertaken in the first phase of this study to characterize the LCLV operational performance. The second phase of this study will involve the evaluation of the LCLV as a component in optical image processing systems. An analysis of the intensity to amplitude mapping and of its consequences in both the output Fourier and image planes is presented. Measurements showed a lack of symmetry in the intensities of the plus and minus one diffraction orders in the output Fourier plane and a strong input light intensity dependence of the phase of the output light. An appreciation of these points is necessary for proper use of the LCLV in an image processing system.
Interferometric Determination Of Anchoring Energy In Nematic Cells
M. Warenghem, C. P. Grover
A simple interferometric technique is developed to study the weakly anchored nematic liquid crystal behaviour. The Freedericksz transition threshold and the thickness of the wedged nematic sample are measured by recording its birefringence fringe pattern as a function of angles of incidence of the input beam and its optic axis. These values have been used to determine the anchoring energy coefficients.
Specifying Electronic Autocollimators
Thomas H. Thurston
Specifying an electronic autocollimator for optimum performance in a given application involves an often bewildering choice of performance trade-offs. This paper, intended to be primarily tutorial, will proceed from a brief description of the operating principles and advantages of electronic autocollimators to a discourse on performance specifications and trade-offs. Primary specifications are sensitivity, data bandwidth, angular measuring range, acquire range, and mirror distance. Secondary specifications include size, objective lens focal length, weight, materials, and vacuum or space rating. The trade-offs between specifications, arising from the requirements or constraints imposed by the applications, will determine the ultimate performance of the autocollimator.
Film Thickness And Refractive Index Standard Reference Material Calibrated By Ellipsometry And Profilometry
G. A. Candela, D. Chandler-Horowitz, D. B. Novotny, et al.
A Standard Reference Material (SRM) has been designed and fabricated and will be certified for thickness and refractive index using a highly accurate ellipsometer. The SRM consists of a three-inch diameter silicon wafer with a silicon dioxide film of uniform thickness. The design and preparation of the SRM are discussed and the ellipsometric measurement results and their comparisons with stylus profilometry are presented, along with the precision of the measurements. The ellipsometric accuracy depends upon the wafer oxide film, the model that represents the film-interface-substrate system, and the methods used to make the measurements. When the optical thickness, as determined by the ellipsometer, is compared with the mechanical thickness, as determined by the stylus profilometer, both the correct sample preparation and correct model are important in order to obtain high accuracy. This SRM will be available initially in three nominal oxide film thicknesses of 50, 100, and 200 nm. The SRM can be used to calibrate many different optical and mechanical thickness monitoring instruments as well as ellipsometers for which it was specifically designed.
Waveguide Applications Of Magnetooptic Effects In Thin Films With Different Crystallographic Order
Lucjan Grochowski, Wojciech J. Bock
The paper presents results of magnetooptic effects observed in monocrystalline, polycrystalline and amorphous thin films as applied for integrated optics & fiber waveguide technologies. The reported investigations were carried-out using epitaxial layers of ytrium iron garnet (YIG) doped with Gd and Ga on GGG substrate, polycrystalline layers of MnSb and amorphous FeNi permalloy layers deposited on a glass substrate (BK-4). Since materials under consideration were sufficiently representative for the whole class of magnetooptic thin films, the paper presents comparative study of their use for telecommunication as well as for sensor applications.
The Switching Characteristics Of The Fastest T.N. LCD Operating From -60°C To +80°C
Birendra Bahadur, Shashank Jatar, Mark Everett
The paper reports on the optical switching characteristics of the fastest TN cell. The display utilizes a special superfast mixture developed by Data Images. Equipment was designed to monitor the switching characteristic from low to high temperature. The design is described in the paper. Some of the physical properties of the superfast fluid are mentioned and compared with those of commercially available fast mixtures. The D.I. superfast line of display has also ultra-thin spacing which increases the viewing angle and reduces the switching times. The display operates from -60°C to +80°C. It has a total on + off time (including delay) of approximately 20 msec at room temperature and approximately 1 sec at -40°C. This type of display eliminates the need of a heater for low temperature operation of LCDs and is very useful for wide range operating conditions.
64 x 64 InSb Focal Plane Array With Improved Two Layer Structure
S. Shirouzu, T. Tsuji, N. Harada, et al.
An InSb photovoltaic sensor shows high performance in quantum yield and diode electronics for medium wave IR and thermal imaging in the 3 to 5 μm range. A 64 x 64 element InSb focal plane array has been developed which has succeded in reproducing TV images in a 3 to 5 μm wavelength range with fine detail using the standard 1/30 second frame time, by employing a newly designed face to face electrical interconnection technique which uses thin islands of copper and indium layers on a Si-CCD substrate instead of ordinary tall indium bumps. The InSb diode array fabrication is based on the planer technique which has an advantage of high integration of diodes over the mesa construction. Their excellent diode back-bias characteristic and its uniformity within the array have been attained by Mg ion implantation and double passivation layers of InSb anodic oxide film and Al203 sputtered layer. These diodes, with less than 50 μm wafer thickness, show uniform quantum efficiency of more than 50 percent in the 2.5 to 5 μm wavelength region with backsurface illumination. This diode array, with a sapphire window back-up plate is bonded to the Si-CCD substrate to form the two-layer laminated construction. The electrical interconnection between the diodes and the CCD has shown almost no loss, even after more than one hundred thermal cycles to 77K. With proper control of created IR charge injection into the CCD well and with the use of a 3.5 to 4.0 μm band-pass filter, a noise equivalent temperature difference (NEAT) below 0.07K has been obtained.