This PDF file contains the editorial “Editorial: Contributed Papers and Special Section Papers--An Analysis” for OE Vol. 33 Issue 04

The electromechanical equations governing the motion of the surface of a deformable mirror, due to the activation of a piezoelectric or electrostrictive actuator mechanically located between the mirror surface and the mirror substrate, are derived in terms of the fundamental electromechanical parameters of the mirror-actuator configuration. The equations of motion are solved in the frequency domain and the solutions show reasonable agreement with experimental data such as Bode plots, which characterize the frequency dependence of the amplitude and phase of the mirror surface motion, and with frequency-dependent impedance measurements. Time-domain solutions are used to construct time histories of an actuator under a step-voltage input.

An empirical formula for calculating the IR extinction of aerosol particles of brass 70 Cu/30 Zn over the IR frequency range was derived based on extensive calculations made on a body-center-like model having a widely varying number of particles ranging from 3.2 x 10⁴ to 2.56 x 10⁵. The expansion coefficients in the empirical formula ere determined by the least squares curve fitting of numerical data obtained using the finite difference time domain (FDTD) method. The formula satisfied the frequency dependence of the extinction in the frequency range from 2.143 x 10¹³ to 3.75 x 10¹³ Hz. The expression for the resonant particle size (d₀) and the constant coefficients in the empirical formula were derived in terms of the wavelength λ, particle size d, and number of the primary particles N of aerosol particles. Numerical results that were obtained from the empirical formula generally agreed well with those calculated by the FDTD method for aerosol particles of brass 70 Cu/30 Zn with a magnitude of particle size in the range from 0.02 to 0.5 μm. The average error in the extinction calculation was less than 5%. The formula thus provides a simple and inexpensive method for calculating the IR extinction of aerosol particles, which otherwise requires complicated and expensive calculation methods.

We investigated the optical power transmission and conversion efficiency between the lower and higher modes in a multimode symmetric Y-junction waveguide. Using the overlap integrals of the fields of the incident and transmitted guided-wave modes at the Y junction, we obtained a first-order approximation of the transmission characteristics and found that there is a possibility of transmitting a useful amount of the incident optical power into the output branching waveguides at very large branching angles. Results showed that an appropriate branching angle of the Y junction can be used to selectively transmit the waveguide modes into the output branches. We developed a very simple model using ray optics to explain the results on a more intuitive basis.

The geometrical optics design of a focusing grating coupler (FGC) is discussed for the situation in which the shape of the guided and free-space pencil and the diffraction geometry are general. A function that describes the so-called optical path-length defect in a general point of the FGC yields the spatial frequency components after differentiation. The wavefront diffracted by the FGC is analyzed at large values of the numerical aperture of the free-space wave by means of ray tracing. Spatial variation of the wave amplitude over the wavefront due to the progressive diffraction of the guided wave is not taken into account. Tolerances on the wavelength drift of the source, the waveguide properties, and the source position are given for an integrated optical disk pickup equipped with an FGC.

We theoretically analyze the behavior of a hybrid optical bistable device that uses a tunable directional coupler filter as a modulator. The device is shown to have a great potential for applications in optical computing and optical communications. The output intensity dependencies on different input parameters are plotted and their basic features are exploited in imaging applications such as optical logical gates and other optical circuits. The spectral dependence of the pulse response of the bistable device is emphasized, suggesting the design of a very sensitive wavelength sensor.

We present the first experimental demonstration of an S-shaped two-coupler single-mode optical fiber ring resonator. The full resonances of the transmitted and reflected output intensities under different resonance conditions, Butterworth-like response, and the splitting of the resonance peak of the reflected output intensity are observed. A comparison between the observed results and the theoretical results shows that they are in reasonable agreement.

The complex transmittance of an Epson liquid crystal television (LCTV) is determined as a function of the video drive signal. Several different operating configurations of the LCTV are established, and their usefulness as operating modes for spatial light modulators in the input and filter planes of a hybrid correlator is discussed. A high-stability phase measurement scheme is developed to determine the operating curves, and this system is presented. This measurement scheme is designed so that a fully characterized LCTV could be assuredly moved into the optical correlator. This allows filters to be calculated for the correlator using the exact physical action of the modulators. The transient response of the LCTV to field-rate changes in the video signal is also presented. It is observed that the switching speed of the liquid crystal molecules is a fundamental limitation on the operating speed of these devices.

We propose an optical heterodyne method to measure the magnetostatic field using a magnetic fluid with high sensitivity. This measurement system consists of a stabilized transverse Zeeman laser, an optical isolator with a Faraday rotator and a half-wave plate, and a sensor. The probe light passes through the magnetic fluid twice in the sensing part. These optical components are connected by the polarization-maintaining fiber. This fiber sensor is independent of temperature and external stress because both the reference and probe beat signals are compared for their phase difference using two bundle fibers. The magnitude of the magnetostatic field as well as its azimuthal direction is obtained from the phase difference. The results obtained are a resolution of ~0.1 Oe and a measurement of up to 500 Oe.

Two optical fiber pressure sensor techniques are applied to the measurement of the distributed pressure of an O-ring. These sensors are polarimetrically and interferometrically based. Experimental results are presented for measuring the pressure exerted on an O-ring placed in a vacuum chamber and are compared with analytical results. Resolution and dynamic range of the fiber sensors are discussed.

A new method for measuring the straightness of travel of a moving table is described. The method uses two conjugate beams diffracted from a holographic grating that is mounted on the moving table. The intensity of two-beam interference is measured and the transverse displacement of the table is calculated from the change in intensity. The system is theoretically capable of measuring the transverse displacement to nanometer-order accuracy. Experimentally, a transverse displacement measurement with an accuracy of 0.12 μm was obtained over a staged travel of 100 mm.

In some applications of diffusers, it-is desirable to minimize the diffuse back reflection of light. Use of polarized light is one way to reduce this back reflection. To that end, the effect of diffusers on polarized light is studied experimentally. Diffusers based on ground glass, white plastic containing scatterers, and holographic optical elements are considered. The ground glass and holographic optical element (HOE) diffusers preserve polarization in the diffusion process, but the white plastic does not. Diffuse back reflection from ground glass or holographic diffusers can be significantly reduced using an isolator based on a quarter-wave plate.

A two-step method for fabricating miniaperture on-axis holographic lenses with high numerical apertures is presented. The first step is to record a bifocus off-axis master holographic lens using a plane wave and a divergent spherical wave. The second step is to record the miniaperture on-axis holographic lens using the conjugate reconstructed wave of the master holographic lens. A holographic lens array is made in our experiments in which the numerical aperture of each lens in the array reached 0.31.

A method for isolating three-dimensional features of known height in the presence of noisy data is presented. The approach is founded on observing the locations of a single light stripe in the image planes of two spatially separated cameras. Knowledge relating to the heights of sought features is used to define regions of interest in each image, which are searched to isolate the light stripe. This approach is advantageous because spurious features that may result from random reflections or refractions in the region of interest of one image usually do not appear in the corresponding region of interest of the other image. It is shown that such a system is capable of robustly locating features such as very thin vertical dividers even in the presence of spurious or noisy image data that would normally cause conventional single-camera light-striping systems to fail. The discussion that follows summarizes the advantages of the methodology in relation to conventional passive stereoscopic systems as well as light-striped triangulation systems. Results that characterize the approach in noisy images are also provided.

The integration of optimization techniques for use in digital image correlation problems in experimental mechanics is discussed. Stereo sets of images of a speckle pattern on a loaded body are correlated using four types of optimization routines. The results obtained using the gradient-based first-order method and nongradient-based pattern search, simplex, and Powell's methods compare extremely well with the original experimental results. The effectiveness and accuracy of these different optimal image processing techniques have also been analyzed and found suitable for this example

A hybrid optical and digital image recognition method (based on optical Fourier diffractometry) applied to the detection of disease-induced pathological changes in bones is presented. X-ray bone images are analyzed in a new type of computer-controlled diffractometer. The set of image parameters, extracted from the diffractogram, is evaluated by statistical analysis. The synthetic statistical image descriptors, constructed based on the groups of training images, enable recognition of bone samples with degraded bone structure and then recognition of disease. About 89% of images were classified correctly. After optimization, this method can be applied to a computer-aided medical diagnosis process.

Over relatively long paths near the earth's surface, atmospheric radiance can be a significant contributor to a poor SNR. These radiant emissions are primarily from atmospheric constituents such as H₂O and CO₂. Many commercially available IR imagers utilizing mercury-cadmium-telluride scanning detectors are not optimized for long horizontal path research. The degradation in the detected SNR due to atmospheric effects makes it advisable to use detectors that are sensitive in wavelength regions where the atmospheric attenuation is minimal. Through proper doping of the detector and cold finger filtering, there is an increase in the magnitude of the detected target radiance and a much more favorable ratio of target-to-path radiance that directly affects the image quality. We present a methodology that has resulted in a computer algorithm that is used to predict optimal system response conditions. Preliminary results show a 5% to 10% enhancement of the target-to-background apparent temperature or ΔT in the 8- to 12-μm region over a relatively short path.

A six-feature all-sky star field identification algorithm has been developed, integrated with a CCD-based imaging camera, and tested at the Table Mountain Observatory, California. Calibration of the CCD-based camera to minimize the error in the measured star parameters due to instrument error and experimental conditions is discussed. A set of observatory tests on star fields with this intelligent camera is described.

The theoretical background and the procedure for executing a new moiré interferometry method, which combines the advantages of geometric and traditional moiré interferometry, are reported. The method uses a low-spatial-frequency steep grating of about 40 lines/mm on a mirror-finished specimen surface to achieve high-contrast moiré fringes. A special four-beam moiré interferometry bench is designed for the low-grating frequency used. An application to experimental fracture mechanics analysis is briefly discussed.

A new tool for experimental mechanics called substrate guided wave (SGW) holo-interferometry is described. The approach relies on recording and reconstructing time-average, double-exposure, and realtime holograms using light waves guided to the hologram by a dielectric sheet or substrate waveguide. The study illustrates that SGW holo-interlerometry can be used to isolate the reference wavefront from the environment surrounding the hologram and can be applied to measure the mechanical properties of the substrate itself. These attributes are discussed along with experimental work performed to develop and refine the technique.

Experimental results of a Q-switched NYAB self-frequency-doubled laser end-pumped by a laser diode array (LDA) are reported. A cw 0.5-W LDA was used as an end-pumping source. An average output power of 6 mW and repetition rates of 16 kHz at 0.53 μm were achieved. The pulse durations at 1.06 and 0.53 μm were 45 and 25 ns, respectively, and a peak output power at 0.53 μm of 20 W was achieved at the Q-switching repetition rate of 100 Hz.

We used a limit parameter structure hollow-bore ridge waveguide array to obtain a beam output with a single-peak highly spatially suppressed far-field distribution and a near-field distribution of 13 spots. We achieved 44 W of output power and more than 10% efficiency from a 200-mm gain length.

Properties of lasers with frequency-shifted feedback are discussed. The analysis concentrates on the passive characteristics of the cavity. Particular emphasis is given to the case in which the frequency shift is small compared to the free spectral range of a normal Fabry-Pérot cavity with no frequency shift.

Beam waist shift in optimum focusing of Gaussian beams is investigated under different conditions. We show that the minimum spot size on a target is only distinct from the beam waist when the target distance is fixed and either the lens focal length, the input beam waist, or the wavelength is varied.

The human retina adaptively processes visual data even if the environmental or imaging conditions are far below ideal. The unique ability of eyes to adapt to poor light and environmental conditions for processing of low-level information is important for edge detection and recognition. This is accomplished through different responses of photoreceptors and adaptive center-surround responses of cells organized in four major layers. We present a structured neural network for image and edge enhancement that is derived from the model of biologcal understanding of retinal layers. The image is described by a set of interconnected neurons with their values equal to the gray-level values of corresponding pixels. The first-order and second-order contrast links are defined among the neurons, which are analyzed for changes in their values in the adaptive constrained environment. Each selected neuron is analyzed only once per iteration in which its value may be readjusted by incrementing or decrementing the current value. As a result, at the end of each iteration, the image data are reorganized for better contrast and image features. We present the structure and algorithm of the proposed neural network with various experimental results showing the capability of such a network to enhance the gray-level images. The method presented is suitable for computerized digital processing of gray-level images for enhancement.

Optical testing involving interferometric fringes is often adequate to obtain a quantitative estimate of a critical parameter such as "asphericity," i.e., the deviation of a surface from a perfect sphere at a specific radial distance. We propose a two-stage neural network solution that can provide such a quantitative output. The first stage is a self-organizing map network that efficiently performs fringe thinning by detecting fringe maxima even in the case of noisy low-contrast images. The second stage is a back-propagation-trained neural network that "learns" to interpret the thinned fringes represented by polynomial coefficients. Fringe patterns from a sample set of optical components, with known parameters that cover a wide range, are used for training. Experimental results were obtained in the case of fringe patterns from a Talbot interferometer for testing aspheric glass molds used in ophthalmic lens making. On test molds with asphericity values close to 0.050 mm, the difference between values obtained from the neural network and by contact measurement was less than 0.002 mm.

Experiments were conducted to verify a theoretical model on the injection efficiency of sources in the cladding of an optical fiber. The theoretical results predicted an increase in the injection efficiency for higher differences in refractive indices between the core and cladding. The experimental apparatus used consisted of a glass rod 50 cm long, coated at one end with a thin film of a fluorescent substance. The fluorescent substance was excited with side illumination, perpendicular to the rod axis, using a 476-nm argon-ion laser. Part of the excited fluorescence was injected into the core and guided to a detector. The signal was measured for several different cladding refractive indices. The cladding consisted of sugar dissolved in water, and the refractive index was changed by varying the sugar concentration in the solution. The results indicate that the power injected into the rod, due to evanescent wave injection, increases with the difference in refractive index, which is in qualitative agreement with theory.

A method of measuring optical aberrations using axial intensity information near paraxial focus is described. This method can be applied to systems with or without central obscurations. The axial intensity profile can also be used to determine the location of paraxial focus in a centrally obscured system, a measurement that is difficult to achieve using other methods. The experimental data demonstrate good agreement with theoretical predictions.

Measurement of dihedral angles of a cube-corner retroreflector with curved surfaces is discussed. A simple method for measuring a dihedral angle from an interferogram is given based on theoretical consideration. A general method to obtain three dihedral angles by means of least-squares fitting of the interference fringes is also described. The method is tested by means of simulation data.

A recently developed technique for fringe analysis based on a digital phase-locked loop is applied to detect the ray aberration of modulated Ronchi rulings. The Ronchi ruling is placed outside the caustic, and the shadow of the ruling is imaged directly into a two-dimensional CCD video array for further processing. The CCD array is placed at a distance of a few centimeters behind the Ronchi ruling; therefore, reasonably well-defined modulated fringes are obtained into the CCD sensor. Moreover, for small wave aberrations and coherent illumination, the first Talbot image of the ruling may be imaged over the CCD to increase the sensitivity of the test. By means of the experimental setup suggested herein, we obtain slightly modulated fringes. These fringes are demodulated using a highly sensitive digital phase-locked loop. Consequently, the transversal aberration along the direction perpendicular to the grating is found continuously across the entire image; that is, no unwrapping process is required, given that it is implicit within the phase-locked loop technique. Additionally, the same scheme with minor modifications may be used for null testing of aspheres.

The use of moiré deflectometry for quality control applications is investigated. Moiré deflectometers were designed and used in the experiments, most importantly the retroreflected moiré deflectometer. Two parts were addressed: phase object analysis and specular object analysis. First, a density variation in a piece of glass (phase object) was examined. Moiré deflectograms were obtained using a conventional moiré deflectometer coupled with a retroreflector and a retroreflective deflectometer with a white light source. Ray deflection versus position graphs as well as 3-D ray deflection maps were generated. Second, both a large and a small outdent on a specular surface were investigated. The attempt to replace the laser with the white light source in a traditional moiré deflectometer did not yield any useful results. Moiré deflectograms were, however, obtained with the use of the traditional moiré deflectometer and with the arrangement employing a retroreflector. Slope versus position graphs were generated and compared to a calibrated artifact. The comparisons were very poor. Despite these results, moiré deflectometry can be used to locate such flaws.

We present an optoelectronic feedback loop that uses a mean field annealing algorithm for extracting features from noisy images. The configuration is analyzed and novel methods to reduce optical misalignment problems and intensity distortions are presented. Experimental results are reported and are found to be in good agreement with those obtained in computer simulations.

The Digital Imaging and Remote Sensing Laboratory at the Rochester Institute of Technology is developing a new airborne multispectral imaging scanner. One of the most critical components of the scanner system is the scan mirror assembly. The scan mirror must satisfy at least two basic requirements: (1) optical image quality: the image blur caused by deformation of the mirror surface should not exceed the detector size, and (2) mechanical stability: the scan mirror assembly must be dynamically balanced to prevent vibration due to centrifugal force. Due to the large size (6-in. diameter) and high rotation speed (4800 rpm), these two requirements are difficult to meet at the same time. We present a modeling approach for evaluation of mechanical design alternatives using image quality metrics. Several mirror design configurations were evaluated. Each configuration was modeled using a finite element analysis method. The deformation of the mirror surface as well as the centrifugal forces were calculated. The image quality was modeled using optical image formation theory. The modeling approach was validated experimentally. A 3-in. scan mirror was modeled using the same procedures, and the line spread function (LSF) of the scan mirror due to the deformation at high speed was calculated. The actual LSF at that speed was also measured using a CCD linear array camera. The test results obtained with a 3-in. mirror agree with the model within 20% in the width of the LSF. (Approximately 500% error is observed if no distortion is assumed.)

Optical designs often consist of lenses that are mounted in a common lens barrel. For lenses having diameters greater than 20 cm and subject to large temperature differentials and/or shock loading, standard metal retainer ring mountings may not be acceptable. An alternate method for mounting these lenses is to mount each individual lens in its own subcell using an adhesive and then to use an interference or press fit to mount these subcells in the lens barrel. When mounting lenses in this manner, it is necessary to evaluate the stress induced in the glass and the residual difference in the optical path. A closed-form analytical derivation was made for a simple lens mount that relates the allowable magnitude of the interference fit to the stress in the glass. This theoretcal expression was then modified using finite element models for use with complex lens designs. Moreover, since lens mountings may require the use of relatively thick layers of flexible elastomer to mount the lenses in their individual cells to prevent large thermal and/or mechanical stresses, the equation for determining the decentration of lenses mounted in circumferential flexible elastomers is also derived. The theoretical expression was used to verify finite element models that then may be used for more complex mounts.

Blazed Fresnel zone lenses for the 1.5-μm wavelength were fabricated in quartz glass by means of microstructuring technology. The blazed profile in each zone of the lenses was approximated by two, four, and eight discrete levels. The effects of fabrication errors, such as depth and alignment errors, on the diffraction efficiency of the different Fresnel zone lenses were investigated. Further the location and intensity of the parasitic foci appearing due to the discrete level approximation are calculated. Theoretical results along with experimental measurements are presented.

A scheme for a three-axes orientation measurement device that provides low sensitivity of orientation measurement errors to gyro errors is analyzed. The low-sensitivity property of the device is provided at the expense of continuous, one-directional rotation of the gyro unit. Gyro unit rotation enables measurement of spatial orientation when all gyros but one fail. This results from the fact that three components of the moving vehicle full-angle speed vector modulate three different parameters of the output signal of each gyro. The results obtained are significant for the development of small-sized strapdown inertial navigation systems that have high accuracy and reliability and employ low-cost optical gyros-laser, fiber optic, and integrated optic gyros.

A review of the basic issues implicit in the design of confined state photodetectors is presented. The basic device structure of a confined state photomultiplier consists of repeated unit cells each comprised of a narrow-gap semiconductor layer sandwiched between barrier layers of wider band-gap material. Gain in these structures is derived through carrier multiplication via impact excitation of confined electrons out of the narrow-gap semiconductor layer. Different device designs are considered in an attempt to maximize the device gain at minimum dark current. In some implementations, the barrier layers are chosen to be graded such that the leading edge discontinuity is at least twice that at the trailing edge of the well forming an asymmetric well design. We find that an asymmetric well design offers a much higher impact excitation of electrons confined within the well at a lower operating voltage than a symmetric well design, however, at the expense of increased dark current. Quantum versus classical confinement of the electrons within the well is also investigated. Though the ionization rate within the classical confinement design is less under comparable conditions to that in the quantum confinement design, the dark current is much less within the classical structure than in the quantum structure, giving a higher excitation-rate-to-dark-current ratio. The gain and dark current are investigated in structures made from GaN/AlGaN, HgTe/HgCdTe, and GaAs/AlGaAs.

An enhanced optical effect is observed in a high electron mobility transistor device when the radiation is allowed to fall on the gaps of the source, gate, and drain of a n-AlGaAs/GaAs system. A 2-D model is presented considering a realistic velocity field relation of carriers in the n-AlGaAs layer. Due to the incident radiation, a photovoltage is developed across the heterojunction in addition to band-edge discontinuity between the n-AlGaAs and GaAs layers. This photovoltage drags the electrons from the n-AlGaAs layer into the heterointerface, thus significantly enhancing the sheet concentration of 2-D electron gas. The drain current and transconductance of the device increase considerably. Plots have been made for the I-V characteristics and the transconductance versus gate voltage. Also, a ratio of drain current under illumination and drain current under a dark condition has been plotted against the input optical power density, which indicates that the overall gain of the device is enhanced by a factor of more than 10 compared to its dark case.

A new platform stabilization approach is described where miniature, low-cost, linear accelerometers are used (instead of gyroscopes) for line-of-sight (LOS) stabilization. This is accomplished by placing the accelerometers at strategic locations and combining their outputs so that angular motion is determined from linear acceleration measurements. The control system uses the sensed angular accelerations to generate movement commands for the gimbal servomotors in the stabilization platform. This counterrotates the imaging device to stabilize its LOS. The use of accelerometers allows the servo system to operate in an acceleration control mode, which is more desirable than position or velocity control modes, typical of gyro-based systems, since this increases stabilization bandwidth. Substituting gyros with accelerometers provides the additional benefits of lower sensor cost, weight, and power consumption, better temperature characteristics, more robustness, and higher shock resistance.

The copolarized backscattered intensity from surfaces composed of metallic particles on conducting flat substrates is analyzed experimentally as a function of the incidence angle. The analysis is done for particle sizes smaller than, comparable to, and larger than the incident wavelength (0.633 μm) and for low particle surface densities. Numerical calculations based on the extinction theorem for a onedimensional surface model consisting of an infinitely long cylinder located on a flat substrate for the same optical constants used in the experiment are also presented for qualitative comparison with the experimental results. This serves to analyze the effect of particle aggregation. For the surfaces with particles smaller than the incident wavelength, conclusions are drawn concerning the possible relevance of this study in radar wave scattering from the sea surface.

The ability to measure in-plane displacement on the surface of a rotating structure under service conditions and real-time analysis to provide component strain distributions would form the ideal experimental optical technique. Pulsed laser electronic speckle pattern interferometry, which can display interference patterns for in-plane displacement in conjunction with the Fourier transform method of fringe analysis, is one attractive approach that is coming closer to this ideal. The optical system used enables a wide range of rotational speeds to be covered with tangential velocities up to 300 m/s.

For scanning active imaging systems using direct detection, it is possible to adequately model the expected speckle noise. Modifications are introduced to the theory on speckle originally proposed by Goodman to take into account the scanning effect. The model presented here is verified experimentally for a scanning active imaging system using a CO₂ laser (10.6 μm). A direct relation between the reduction in the speckle noise resulting from the scanning process and the imaging resolution is demonstrated.

Detection and identification of objects in images formed by coherent imaging systems are complicated by the presence of speckle. Speckle not only complicates these problems for human observers, but also for machine detection and identification algorithms. We investigate optimal statistical tests for object discrimination and orientation determination in speckle and compare their performance to that of human observers for the same problems. We formulate maximum likelihood tests for determining the orientation of an object and for discriminating among a set of known objects in a speckled image. We then analyze the performance of these tests to study the system requirements for reliable object discrimination and orientation determination. Next we generalize these tests and their corresponding pertormance analyses into three broad classes of pattern recognition problems, corresponding to orthogonal, antipodal, and biorthogonal signal problems in statistical communications theory. These generalizations make the design and analysis of a broad range of object discrimination and orientation determination straightforward. Finally we compare the performance of these tests to the results of Korwar and Pierce for human interpretation of objects in speckled images. We note that for fixed image contrast, number of looks, and image size in pixels, object shape has no effect on machine detection performance. This is not true for the human observer.

In recent years, with the development of satellite and computer technology, Earth observation and atmospheric research have become highly dependent on digital imagery. One of the primary interests in digital image processing is the development of robust methods to perform feature detection, extraction, and classification. Until recently, classification methods for cloud discrimination were mainly based on the spectral information of the imagery. However, because of the spectral similarities of certain features (such as ice clouds and snow) and the effects of atmospheric attenuation, multispectral rule-based classifications do not necessarily produce accurate feature discrimination. Spectral homogeneity of two different features within a scene can lead to misclassification. Furthermore, the opposite problem can occur when one feature exhibits different spectral signatures locally but is homogeneous in its cyclic spatial variation. The exploration of spatial information is often advantageous in these discrimination problems. A texture-based method for feature identification has been investigated. This method uses a set of localized spatial filters known as 2-D Gabor functions. Gabor filters can be described as a sinusoidal plane wave within a 2-D Gaussian envelope. The frequency and orientation of the sine plane and the width of the Gaussian envelope are determined by the Gabor parameters. These tunable channels yield joint optimal information both in the spatial and the frequency domains. The new method has been applied to the thermal channels of the NOAA Advanced Very High Resolution Radiometer data for cloud-type discrimination. Results show that additional texture information improves discrimination between cloud types (especially thin cirrus).

For the wavelength region above the Si-L edge normal incidence, soft x-ray mirrors are produced with peak reflectivities close to 60%. The multilayer systems consist of molybdenum and silicon and are fabricated by electron beam evaporation in ultrahigh vacuum. A smoothing of the boundaries, and thereby a drastic enhancement of the reflectivity, is obtained by thermal treatment of the multilayer systems during growth. The thermal stability of the multilayer stacks could be improved considerably up to 850° C by mixing Mo and Si in the absorber layers and producing thus Mo_xSi_y/Si multilayers with x and y denoting the amounts of Mo and Si in the absorber layer, respectively. First attempts are reported to produce mirrors with a bilayer thickness of 2.6 nm. An improvement in the quality of these interfaces can be obtained by bombardment with Ar⁺ ions. We report on normal incidence reflectivity measurements of the mirrors with synchrotron radiation and finally on the normal incidence diffraction efficiencies of a Mo/Si multilayer coated grating, for which values of 5.5% are achieved for the + 1'st and - 1'st diffraction orders.

Liquid crystal (LC) spatial light modulators (SLMs) are addressed optically with semiconductor thin-film photosensors incorporated into the devices. Nematic LCs, which are insensitive to the polarity of the applied voltage, are addressed by optically modifying the effective resistance of the photosensors to be much smaller than or much larger than a threshold value. Much faster ferroelectric LCs, which are polarity sensitive, are addressed by supplying sufficient photogenerated charge. Because the spatial resolution of the devices decreases rapidly with increasing mobility of carriers at the photosensor/LC interface, very low mobilities, less than 1 cm² V^-1 s^-1, are required. Photodiodes of hydrogenated amorphous silicon in p-i-n, Schottky, and metal insulator semiconductor configurations form practical photosensors for optically addressed SLMs. Thin-film photoconductors, having nonblocking contacts, cannot be used in many cases because of their large dark currents.

In the present study, the rf plasma chemical vapor deposition technique is applied to directly deposit a diamond-like carbon (DLC) film onto a zinc sulfide (ZnS) substrate with excellent adhesion. Great attention is paid to the investigation of the correlation between the deposition process parameters and the structure and properties of DLC film, and of the optical spectrum characteristic of DLC films appropriate to protect IR window materials. The experimental results show that the refractive index, microhardness, and growth rate of DLC films increase with increasing dc bias voltage. The IR transmittance of the ZnS substrate with DLC film has been increased to some extent between 3 and 12 μm.

Photothermal displacement microscopy has been used for the characterization of ZrO₂ and MgF₂ single-layer thin films to detect absorption inhomogeneities at λ=514 nm. Images are presented for films of λ/2, λ, and 2λ optical thickness deposited on BK7 glass and SQl quartz substrates. Applying modulation frequencies ranging from 1 to 100 kHz a lateral resolution of several micrometers was obtained. We found that the size and density of the absorption inhomogeneities as well as absorptance depend strongly on the deposition process and weakly on the substrate material. No dependence on thin film thickness was found. The apparent defect density varies with the modulation frequency demonstrating the capability of the photothermal method to localize absorption in various depths of the thin film. Defect densities derived from the photothermal measurements are compared with results from total integrated light scattering (TIS) experiments performed on various samples at is λ = 632 nm. TIS intensities for MgF₂ films on glass substrates were about one order of magnitude smaller than those from films on quartz. The latter revealed strong long-range (1-mm) variations of the light scattering intensity. This finding is in accordance with the absorption measurements.

Quantitative and visual data of artificially forced instabilities are acquired in a flat plate boundary layer in air. For the first time, particle image velocimetry (PIV) allows the instantaneous recording of a complete velocity field. With this technique, quantitative data are obtained within the boundary layer and very close to the wall. By using a light sheet technique it is possible furthermore to obtain visual data. Reproducible and constant conditions in the development of the instabilities are achieved by forcing the boundary layer with well-controlled disturbances. These disturbances are generated with an arrangement for acoustic excitation.

An optical noncontact 3-D range digitizer based on projection of 2-D structured light patterns and multiplexed charge injection device (CID) camera sensors has been developed. The system acquires digitized data in 0.75 5 and allows 360-deg examination of the subject's head and facial surface features in less than 1 s, making it suitable for digitizing children as well as adults. The resultant 3-D surface data is suitable for computer graphics display and manipulation, numerically controlled replication, and further processing such as surface measurement extraction. The digitizer uses a set of six stationary sensors positioned about the subject. A sensor consists of a pattern projector and a solid state video camera. This device allows quantitative volume measurements and employs no harmful ionizing radiation. The cost of a scan with this technology is substantially less than that of alternative means of collecting 3-D surface data sets, such as by stereometric, moire fringe, and single-point digitization. This system was geometrically designed such that any surlace of the head or facial area was independently digitized by a minimum of two sensors and to capture areas normally occluded with other techniques. The dimensions of the structure were derived to satisfy physical constraints placed on its overall size. The camera and projector orientations in space, the distance from the lens centers to the center of the digitizing volume, and the lens focal lengths were determined analytically. To reduce cost, a standard lens nearest the analytical value was used. Based on the standard size lens, the field of view was calculated.

An optical noncontact 3-D range scanner based on projection of 2-D structured light patterns and multiplexed charge injection device (OlD) camera sensors is developed. The system acquires scan data in 0.75 s and allows 360-deg examination of the object. The resultant 3-D surface data is suitable for computer graphics display and manipulation, numerically controlled replication, and for further processing such as surface measurement extraction. The scanner uses a set of six stationary sensors placed around the object to be scanned. A sensor consists of a pattern projector and a solid state video camera. The projectors are sequenced by a module called the video acquisition and control unit (VAU). This complex system must be accurately calibrated for seamless merging of overlapped surfaces obtained from different cameras. The calibration considerations in such a system are discussed. The calibration is accomplished using statistical parameter estimation algorithms. Known reference objects are used in the calibration procedure.

This PDF file contains the editorial “Book Rvw: An Introduction to Photonic Switching Fabrics," by H. Scott Hinton for OE Vol. 33 Issue 04