Proceedings Volume 1399

Optical Systems in Adverse Environments

Soon Fatt Yoon, M. H. Kuok, Donald E. Silva
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Proceedings Volume 1399

Optical Systems in Adverse Environments

Soon Fatt Yoon, M. H. Kuok, Donald E. Silva
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 1 March 1991
Contents: 1 Sessions, 26 Papers, 0 Presentations
Conference: Singapore 1990
Volume Number: 1399

Table of Contents

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Table of Contents

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Misalignments of airborne laser beams due to mechanical vibrations
Jose Cabrita A. Freitas, Manuel Adler Abreu, Fernando Carvalho Rodrigues, et al.
The effect of mechanical vibrations on the shape characteristics and direction of a laser beam of a particular spectrum of vibration is considered. A detection system designed to collect laser pulses emitted by a pulsed laser diode placed onboard of a jet airplane is simulated experimentally. Results show that the area illuminated by a laser beam can vary quite diversely with the frequency and amplitude of the vibration over the period of detection producing a divergence of the laser beam different from that of a static emitter.
Fungal testing of diode laser collimators
Maria de Lourdes Quinta, Jose Cabrita A. Freitas, Fernando Carvalho Rodrigues, et al.
The utilization of laser systems in adverse environment conditions imposes several project restrictions. In our application, the design of laser collimators was developed according not only with the specified optical, mechanical and electronic parameters, but also, taking into account the specific environment characteristics in which the equipment was to be used, namely, climate, physical elements and biological agents. The utilization of several kinds of materials, like silicone, rubber, PVC, nitro-cellulose lacquers and oil varnishes, may facilitate the attack by fungi and in some special cases by bacteria in humid environments. In this paper the behavior of laser collimators after a severe essay with optimal conditions of humidity and temperature appropriated to growth of fungi is described.
Production of laser simulation systems for adverse environments
Fernando Carvalho Rodrigues, Jose Veiga Simao, Joao Jose Oliveira Pires, et al.
Production methods of laser simulation systems for use in environments with a high degree of agressiveness are reviewed for both terrestrial and airborne applications. Particular attention given to generally accepted standards that take into account the real field conditions of the systems applications. These standards and their relation to the quality control for lasers, electronics, and optics in the most severe environments are used for the laser based simulation systems designed and produced in Portugal.
Real-time automatic inspection under adverse conditions
Fernando D. Carvalho, Fernando C. Correia, Jose Cabrita A. Freitas, et al.
This paper presents the results of a R&D Program supported by a grant from the Ministry of Defense, devoted to the development of an inteffigent camera for surveillance in the open air. The effects of shadows, clouds and winds were problems to be solved without generating false alarm events. The system is based on a video CCD camera which generates a video CCIR signal. The signal is then processed in modular hardware which detects the changes in the scene and processes the image, in order to enhance the intruder image and path. Windows may be defined over the image in order to increase the information obtained about the intruder and a first approach to the classification of the type of intruder may be achieved. The paper describes the hardware used in the system, as well as the software, used for the installation of the camera and the software developed for the microprocessor which is responsible for the generation of the alarm signals. The paper also presents some results of surveillance tasks in the open air executed by the system with real time performance.
Atmospheric effects on laser systems
Robert H. Au
A method to calculate the atmospheric transmission of the laser radar beams has been developed for use in systems analysis. The two way transmission is derived in closed form for the neodymium-glass and the carbon dioxide lasers. This study utilizes the optical properties by previous researchers to obtain a function which can be integrated from the laser radar altitude to the object altitude. The closed form solution facilitates the calculation of the two way transmission of a laser radar with a line of sight oriented horizontally, upwards or downwards. Mathematical constants for the attenuation coefficient are presented for use in calculating other altitude cases. The method can be easily applied to other laser radar frequencies.
Microprocessor-based laser range finder
M. Kameshwar Rao, Siu Chung Tam
This paper describes a versatile, low cost laser range finder, which uses a GaA1As laser diode transmitter operating in the near infra-red region at a wavelength of 820nm. A silicon PIN diode receiver captures the reflected laser pulse from the target and a high speed counter measures the time of flight of the laser pulse. A microprocessor based circuit is employed for automatic calculation and visual display of range distance.
Studies on defocus in thermal imaging systems
B. Venkateswara Rao
A practical problem concerning the loss of image quality due to lack of sharp focus arising out of ambient temperature variation or by human error in mecha nical focussing has been haunting Thermal Imaging System designers. The defocuss effect drops down modulus transfer function (MTF) of optical system considerably which in turn drops minimum resolvable temperature difference (MRTD) , which is a vital parameter to assess the total system performance of thermal imagers. Theoritical studies have been carried out to see the effect of defocuss on MRTD for different detector sizes and different focal lengths keeping the F/No. of optics system same. It is found that per centage of deterioration in MRTD for the depth of focus i.e. 2 >(f/no.)2 governed by optics is not same for different systems though f/no.2is constant. Hence it is understood that the depth of focus formula 2 A(f/no.) governed by optics does not hold good in case of Thermal Imaging Systems. An empirical formula for allowable defocuss for 10% of telerance in MRTD which is a function of not only f/no. but also detector size Ad , focal length of optics 'f' and spatial frequency is derived.
Reconstruction of three-dimensional displacement fields by carrier holography
Zhu Xu, Ke-long Chen, Zhen-chu Wen, et al.
A new method for determining the displacement fields and inspecting defects inside a loaded or heated object is described. The method uses the carrier holography patterns based on image reconstruction theory. For nonpenetrating material the measure value of projected pattern of displacement fields is obtained from projection of the entire deformable body which is convenient for collecting precise and reliable projection data. A reconstruction algorithm assumes the convolution and is based on a Radon inversion formula. The procedure is applied to a cylindrical body subjected to a concentrated compression on the top.
Recording and analysis of (high-frequency) sinusoidal vibrations using computerized TV-holography
Svein Ellingsrud, Ole Johan Lokberg, Hans Magne Pedersen
The RETRA 1000 TV-holography system has been further developed for analysis of high frequency vibrations, using automatic data acquisition. Special phase shift algorithms are executed by means of a PC-based image processing system. The phase shifts are effected by a built in electro-optic modulator, controlled by a two channel high-resolution digital frequency synthesizer. The optical (speckle) and electronic noise is reduced, using an automatic speckle averaging technique. Amplitude and phase distributions can be calculated and presented for frequencies up to 10 MHz. The lower limit for amplitude detection is below 1 nm (for HeNe laser), while the relative phase distribution is given with less than 3° accuracy under stable conditions. We show results where the technique has been used to analyze various vibrating test objects like a ceramic "crystal", a high frequency loudspeaker and finally an underwater acoustic transducer. The crystal had resonant modes from 3,8 to 7,8 MHz
Laser sensing in the iron-making blast furnace
J. Chris Scott
The measurement of parameters such as distance and temperature in the Ironmaking Blast Furnace is crucial to the performance of the furnace. A series of instruments has been designed, built and tested by BHP which perform these tasks optically requiring no physical intrusion into the harsh environment of the furnace. The problem of coupling high peak power Nd:YAG and ultra violet laser radiation into environments consisting of very high water vapour level, acidic, high aerosol loading, and high temperature environments is considered. The performance of two systems enabling distance measurement with sub-pulse length range resolution under the above conditions is discussed in detail. The use of optical fibres to deliver the pulsed energy to and from the environment together with specific window design parameters are also described. A major problem in making time of flight range measurements in very high density aerosol conditions is the signal processing required to extract the target return pulse position from the complex aerosol return signal. Incoherent detection techniques used to achieve this discrimination where target temperatures can exceed 2000°C are discussed. The selection of operating laser wavelength and repetition rate were based on an analysis of the optical characteristics of gases and aerosol forming the measurement environment together with the dynamic behaviour of the high temperature target. The extension of laser radar techniques to optical fibres is discussed and a distributed temperature sensing system is described which measures temperatures up to 250°C with a spatial resolution better than O.Sm.
In-plane displacement measurement on rotating components using pulsed laser ESPI (electronic speckle pattern interferometry)
Richard W. T. Preater
A pulsed ESPI laser for measuring in-plane displacements and strain on rotating components is shown to operate in a very wide range of component speeds and tangential velocities. An optical system based on fiber optics techniques in conjunction with an infrared diode laser can provide clear interface fringes for radial displacements on a rotating component at tangential velocities up to 150 m/s.
Analysis of vegetation stress and damage from images of the high-resolution airborne pushbroom image spectrograph compact airborne spectrographic imager
Michaela C. Mueksch
known Fluorescence Line Imager (FLI), primarily used in water, coastal and ocean applications. CASI has its potentials In vegetation and water monitoring applications, comprising a spectral range from 400 nm to 900 nm with a spectral resolution of 1 .8 nm channel step. A 12 bit dynamic range delivers a high sensitivity down to some nanometers.Slnce the system has free programmable band settings, delivers a real time image during fLight in the so called spatial mode, can be switched over to a spectral mode, Is easily transportable and can be built In In less than one hour In nearly each aircraft, quick and highly Informative images and spectral data can be gained from the environment
Passive range and azimuth measuring system
E. Ronning, Earl J. Fjarlie
The classical rangefinder that uses two telescopes separated by a fixed base distance so as to produce a parallax-angle difference when pointed at a source of interest to determine the range, has been used as the basis of a passive electro-optic range and azimuth finder. The concept, shown in Figure 1, uses: two silicon photodiode focal plane arrays (FPA) each incorporating 256X256 elements (each element being 40 I.tm by 40 tm) , two standard telephoto lenses, two video data formatters (VDF) , two TV monitors for convenience in operating the system (not shown) , two high-speed waveform digitisers, each with a 128 K memory data storage facility, and a host computer driven by algorithms for determining the range and azimuth. The determination takes about six minutes.
Autonomous mobile laser complex
I. H. Fakhrutdinov, A. P. Avdoshin, J. N. Moshin, et al.
An autonomous mobile laser complex design is described which is based on a gas dynamic laser and airplane jet-propulsion engines as a compressed air source. The advantages of this laser complex include the possibility of performing unique operations, long duration operation of the complex in a self-contained mode, and remotely operated treatment.
Applications of laser techniques in fluid mechanics
Weng Kong Chan, C. Y. Liu, Y. W. Wong
Three examples of different applications of laser techniques in experimental fluid mechanics are described including flow field around a proposed heart prostheses, flow field around a model motor vehicle, and flow visualization of the vortex shedding from a delta wing. Velocity measurements of flow around the heart valve prosthesis indicate that the new design is capable of delaying flow separation. Velocity measurements of flow around a model motor vehicle show that separation occurs above the bonnet and at the rear of the vehicle.
Optical fiber radiation damage measurements
Sanath R. Ediriweera, Frank Kvasnik
The results of studies of changes in the spectroscopic properties of commercial fibers are reported. Analysis of the attenuation spectra of various fibers have confirmed the expected different behavior of Ge-doped and pure silica fibers. However, differences in spectra of fibers made nominally from the same materials but using different processes were also observed. It is therefore concluded that the manufacturing process as well as doping determine the relative abundance of Type I and II color-center defects. The Raman spectra of the fibers were also obtained and analyzed. A strong resonant fluorescence at 650 nm, thought to be due to Type II color-centers, was observed in certain fibers. In general the changes in Raman spectra followed the theoretical expectation, however, the differences between fibers could not be entirely attributed to the doping levels. Again the manufacturing process and the subsequent treatment of fibers is thought to be partially responsible.
Study on Hadamard transform imaging spectroscopy
Ji-Zong Wu, Jia-cheng Deng, Ben-zhi Chen
Hadamard transform imaging spectroscopy (HTIS) based on a measuring principle of double coding modulation for light beam imaging is considered. HTIS is capable of providing high signal-to-noise ratios for spectral testing and detecting weak infrared signals. Topics discussed include a reconstruction formula for the images and spectra in the case of longitudinal folded 2D spatial encoding; design considerations of incidence and exit encoding plates; a schematic diagram of self-made setup of HTIS, a block diagram of software and main electronics to automatically control the whole testing process using IBM PC/XT microcomputer; and results of the infrared absorption imaging spectral testing for CO2.
Integrated optics temperature sensor
Antonio d'Alessandro, Marco De Sario, Antonella D'Orazio, et al.
An interferometer temperature sensor based on a semi-asymmetric X junction made of four single-mode Ti:LiNbO3 channel waveguides is described. For a fixed path length difference, the X-cut configuration exhibits a thermal sensibility greater than that of Z-cut interferometer. The X-cut version is found to be superior for both thermal stability and sensitivity.
Influence of dose rate on radiation-induced loss in optical fibers
Henning Henschel, Otmar Koehn, Hans Ulrich Schmidt
To determine systematic trends that possibly allow extrapolation of the results of continuous irradiations to low dose rates four different fibers were exposed to dose rates between 0.05 rd/s and 180 rd/s of a Co-60 source and to the pulsed radiation of a flash X-ray facility. Data obtained show that in some cases extrapolation of the induced losses measured in this dose rate range to higher dose rates yields nearly exactly the results of pulsed irradiations with about 10 exp 11 to 3 x 10 exp 12 rd/s so that the extrapolation down to values of 10 exp -5 seems to be allowed too.
Detection of the object velocity using the time-varying scattered speckles
Takashi Okamoto, Toshimitsu Asakura
The dynamic properties of doubly-scattered speckles produced at the image plane have been investigated by using a scattering model consisting of a coherent Gaussian beam, a cascade of two moving diffusers and a single imaging lens. It is found that, when the point-spread function and the focal position of the lens satisfy certain conditions, three kinds of velocity information, i.e., the velocity of each diffuser, the average velocity of the diffusers, and the velocity difference between the diffusers, can be obtained by measuring a temporal correlation length of the time-varying speckle intensity. Experimental results confirm the theoretical predictions.
Far-field pattern of laser diodes as function of the relative atmospheric humidity
Jose Cabrita A. Freitas, Fernando D. Carvalho, Fernando Carvalho Rodrigues, et al.
The radiation pattern of a collimated diode laser that was used to transmit messages between two points far apart is considered as a function of a driving current, pulse repetition rate, and relative humidity along the propagation path. It is shown that the spatial and energy distribution characteristics of the laser beam projected over long distances are affected by the humidity and temperature conditions of the atmosphere.
Optical computer-assisted tomography realized by coherent detection imaging incorporating laser heterodyne method for biomedical applications
Humio Inaba, Masahiro Toida, Tsutomu Ichimura
The first successful imaging by laser absorption computed tomography of actual in vitro biological objects with two-dimensional resolution has been achieved by means of Coherent Detection Imaging (CDT) method for noninvasive and noncontact biomedical measurements. This novel method is based on the optical heterodyne detection technique and the image reconstruction using the projection slice theorem from sets of line integrals of laser absorption along a large number of rays crossing the object with the parallel beam geometry.
Solid state lasers for field application
Boris N. Motenko, Boris A. Ermakov, Boris Berezin
Lazer heads without forced cooling and of simple design used phosphate neodymium glass of laser rods for pulse rangfinders have been investigated.The headsensure laser performance for 20 years under adverse climatic conditions (t+50 C, relative humiditi of 98%) with an operating time of 4.10
Optical materials for use under extreme service conditions
Leonid B. Glebov, Gury Timofeevic Petrovsky, Oleg S. Tshavelev
A system of real and practical criteria of glass athermality is proposed to determine the value of thermowave aberrations for disc configurations (lenses and portholes). Basic parameters of the most effective Soviet athermal and strong optical glasses intended for various applications are presented.
Integrated optics in optical engineering
Yury G. Popov
The state-of-the-art of the integrated optics allows us today to pass from the demonstration of its performance and possibilities of individual elements to the development of real integrated optical circuits on their basis and to the i r usage in the opt ical instrument engineering. The paper discusses a number of hybrid optical elements which are designed for the improvement of making optical instruments.
Optics in adverse environments
An adverse environment is defined and several examples of optics in these environments are presented. An adverse environment implies external surroundings and differences that are sources of potential disturbance of the optical system. There are three principle stages of increasing perturbation for any optical system subjected to an adverse environment which include satisfactory operation, unsatisfactory operation which returns to satisfactory when the disturbance is removed, and permanently degraded performance. Mechanical and thermal disturbances will exhibit all three stages, and chemical disturbances will frequently not exhibit any appreciable reversability, but an increasing degradation that moves eventually from satisfactory operation directly to permanently impaired.