This PDF file contains the editorial “Editorial: What! Take a vacation! Who...me!?” for OE Vol. 35 Issue 09

This PDF file contains the editorial “Guest editorial: Optical security” for OE Vol. 35 Issue 09

A phase-only referenceless computer-generated Fourier hologram, which gives a nonsymmetric image in the reconstruction process, is known as a kinoform. A new optically variable device designed for optical security purposes is described that is formed from a matrix of kinoforms. The device is characterized by both rainbow holographic effects and hidden features. The first hidden feature is a slit-shaped image, which contains a line of text or other information. Under normal illumination conditions, this first element shows rainbow holographic and kinematic effects. The second hidden feature is a dark image visible at an angular range different than that of the first feature. This second image is faint under white light illumination, but appears clearly in laser light. In the proposed device, both rainbow holographic images and hidden Fourier-plane images are reconstructed from the whole hologram area, which contains a matrix of single superposed recordings. In this way, the use of special encoded subfields that alert counterfeiters is eliminated. Careful analysis of the image and spectral planes of the device made with expensive and specialized equipment may allow imitation of the device using optical holographic techniques. The device is calculated using a modified iterative Fourier transform algorithm and manufactured in a binary or a multiple phase-step technique. We recall several types of optically variable devices and consider their security properties for document protection.

In the optical implementation of image encryption using random phase encoding proposed by Re´ fre´ gier and Javidi the random phase mask is not band limited. Speckle noise can thus destroy optical reconstruction of the encrypted images. We demonstrate encryption of speckle-free kinoforms by smoothed random phase masks. Optical verification of the encrypted images is shown.

A new optical encoding method for security applications is proposed. The encoded image (encrypted into the security products) is merely a random phase image statistically and randomly generated by a random number generator using a computer, which contains no information from the reference pattern (stored for verification) or the frequency plane filter (a phase-only function for decoding). The phase function in the frequency plane is obtained using a modified phase retrieval algorithm. The proposed method uses two phase-only functions (images) at both the input and frequency planes of the optical processor leading to maximum optical efficiency. Computer simulation shows that the proposed method is robust for optical security applications.

A new kind of security hologram using an encoded reference wave is presented. The hologram is produced with the interference of an encoded reference wave and a convergent object wave. The encoded reference wave is formed from a plane wave that has passed through a random phase plate. When the hologram is illuminated with a duplicate of the reference beam, a verification pattern (a bright spot) is produced in the output plane. Only if the random phase plate matches the hologram, does sharp focus emerge. Because the verification pattern is simply a spot peak rather than an image pattern, this kind of security hologram is suitable for machine inspection. Therefore, it can be used for better counterfeit-resistant security codes in the form of embossed easy-to-copy holograms. Initial experimental results are given.

An image encryption and corresponding decoding method applicable to security verification are presented. This method exploits a holographic process in that an encoded image can be regarded as a hologram pattern resulting from interferences between two waves transmitted through a primary identification image and a reference image serving as an encryption key. We show that the proposed method produces a real-valued encoded image, which facilitates card manufacturing. Moreover, due to the fact that data to be used as the encryption key are real, the decoding system is also easily realized with an amplitude type SLM. The proposed method is justified with various simulation results obtained with data of real-positive or phase-only type for encoded image and encryption key.

We describe a 1-D space integrating optical processor that can perform position-invariant 2-D image correlation by 1-D scanning the input image over a 2-D reference image along a coordinate axis, which we shall refer to as the x axis in a Cartesian coordination system. The 2-D reference function is a position-invariant filter that is designed using distortion-invariant pattern recognition techniques to provide tolerance to misalignments along the y axis between the input image and the reference function during the 1-D spatial correlation. Applications of this system to phase-encoded image recognition and fingerprint recognition are described.

A novel photonic security system is described using 2-D spatial codes based on both optical phase and amplitude information. This security system consists of an optical interferometric encoding subsystem that rapidly reads and encodes the 2-D complex-valued spatial code, forming a wideband frequency modulated optical beam and a colinear optical reference beam. After appropriate coherence coding of this beam pair, the light is launched into a low probability of intercept communication channel such as an optical fiber or a narrow beamwidth free-space optical link. At the remote code receiving and data processing site, the received light beam pair is first coherently decoded. Then, a high speed photodetector via optical heterodyne detection generates an encoded wideband radio frequency signal that contains the original 2-D code. Decoding is implemented in parallel via two independent systems. One decoder uses a Fourier transforming lens to reconstruct an electronic image interferogram of the complex-valued user code. This image interferogram is sent to a high speed electronic image processor for verification purposes. The other decoder is a high speed coherent acousto-optic time integrating correlator that optically determines matchmismatch between the received encoded signal and the code signal generated by the electronic database. Improved security to the overall communication network is added by using various keycodes such as a time varying keycode that determines the exact spatial beam scanning sequence required for both proper encoding and decoding of the 2-D code information. This paper describes preliminary experiments using a simple 1-D amplitude modulated spatial code.

The recording and entry of fingerprints into the local and national databases is increasingly relying on optics to simplify and speed up this process. A prototype device for the entry of fingerprints that uses a waveguide hologram as part of the scheme for illuminating the finger is described. The use of the waveguide hologram enables reduction in the size, weight, and energy consumption of a fingerprint entry device (or live scan device). The entry device then becomes highly portable and thus useful in many office and field applications. Coupled with electronic or optical processing and storage along with telephone or radio transmission of the captured fingerprints, rapid identification of individuals becomes a realizable goal. The components required for the prototype holographic fingerprint entry device (HoloFED) including the light source, the illumination waveguide hologram, the imaging system and the storage, and processing system are discussed. Examples of fingerprints captured are shown. The trade-offs necessary for the implementation of the prototype are object-to-image distance, optical efficiency, weight, and cost.

Optical image encryption and security using random phase encoding techniques have been proposed recently. We present optical experimental results for image encryption and security. The results show that for the image encryption, the image can be well encrypted using random phase masks with a limited number of pixels. We also tested the performance of the optical system for security verification in the presence of different types of input noise and distortions such as scratches, fingerprint marks, and bending of the phase mask. The experimental results indicate that for the severity of the noise and the degree of distortion tested here, the system provides good performance in verifying the phase code.

A low-density diffractive optical write-once, read multiple times memory (WORM) is demonstrated that authenticates and secures documents. Furthermore, by encoding the machine-readable optical code, information can be linked to the document. The proposed solution leads to a reliable, high security machine-readable information carrier that is fully compatible with the requirements of typical security documents, such as payment substrates, fiduciary papers, passports, and identity cards. The information carrier is a juxtaposition of diffractive structures. Data are written permanently in an optical memory; the diffractive structure is changed irreversibly through the interaction of a diffractive surface with a beam of laser light. A prototype low-density optical memory based on diffractive structures that are resilient against copying or reorigination is realized for use in securing official travel documents.

We compare the experimental performance of 12 variations of the binary joint transform correlator (BJTC) when used for fingerprint identification. Three hardware architectures were used: a single spatial light modulator (SLM) BJTC, a BJTC using two input SLMs, and a chirpencoded BJTC using two input SLMs. These correlators were implemented on the same hardware setup with minor modifications. With each hardware configuration, four binarization techniques were implemented: global threshold, Fourier plane windowing, frame subtraction, and frame subtraction followed by windowing. A set of 10 experiments was used to characterize the output peak intensity, peak-to-noise ratio, and discrimination ratio. The same set of experiments was run on each of the 12 correlator variants.

A method for the automatic verification of handwritten signatures is described. The method relies on global and local features that summarize aspects of signature shape and dynamics of signature production. We demonstrate that with the addition of our local feature based on stroke direction coding, the performance of signature verification improves significantly. The improvement is comparable with that of more sophisticated algorithms, which require much more computer resources. The current version of the program needs about 150 bytes to store a signature model and has 3% equal error rate. At the 1% false rejection point, the addition of the stroke direction information to the algorithm with only global features reduces the false acceptance rate from 13 to 7.5%. Prior to extraction of stroke direction information, signatures are normalized for position, size, and orientation using their Fourier transform. Such a scheme can also be useful in signature smoothing and compression.

We demonstrate a hybrid electronic-optical real-time system that performs 3-D face recognition. We constructed custom reference gratings that formed a desired moire´ pattern when mixed with images of structurally illuminated faces. The moire´ patterns could be in any form such as, equal depth contours, error maps, or any arbitrary pattern. We demonstrate video methods to generate such error maps in real time, thus developing a real-time automated face recognition system based on the optical processing of arbitrary moire´ contours. We chose the moire´ pattern to be in the form of a Fresnel zone plate, which is displayed on a liquid crystal television. Illumination of this zone plate with parallel coherent light results in a diffracted beam that produces a focused line on a detector. For the matching process, the focal line is compared against a preset threshold. If the confidence is above the threshold, the face is recognized, otherwise it is not.

We implement an optical continuous phase-only composite filter for security verification. An amplitude-mostly liquid crystal television (LCTV) is used for input and a phase-mostly LCTV is used for the phaseonly filter. We develop experimental techniques for optimizing the LCTV modulations and analyze the diffraction of both coupled-mode LCTVs. We use a new procedure for synthesizing the phase-only composite filters. The filter produces a narrow correlation peak without sidelobes. Experimentation results are shown.

Path-integrated atmospheric transmittance for visible wavelengths over a 5.5-km horizontal path is measured using black target contrast ratio. Measurements of on-line particulate distributions by particulate measuring system instrumentation (PMS) and of meteorological parameters are also performed. The extinction coefficients, primarily scattering, of aerosols are calculated using the PMS data, and those arising from molecular absorption are calculated by MODTRAN. Both extinction coefficients—the directly measured path-integrated ones and those calculated from particulate distribution and meteorological parameters near the receiver—are compared. Good agreement exists, especially when relative humidity is low, despite the fact that the second method involves aerosol size distribution by data collected from only a single point along the atmospheric path. Disagreement between both methods under high values of relative humidity can be explained by classification errors of the PMS instrumentation because of changes in the index of refraction of particles in a humid environment. Statistical regression analysis is made relating the measured transmittance values to online meteorological data. A simple and accurate model is obtained to predict dependence of the extinction coefficient on weather. The regression coefficients model shows that other meteorological parameters in addition to relative humidity are responsible for the changes in the atmospheric scattering coefficients. This contradicts the MODTRAN and Kasten-Hanel models for a continental atmosphere, which are based upon specific types of aerosols rather than a mixture of them.

A new approach to designing computer-generated multilevel diffractive elements, in which the phase and the amplitude of the output wavefront can be controlled independently, is presented. In this approach the diffraction efficiency of the elements can be arbitrarily controlled to reach 100% efficiency over the entire element. The approach is based on varying the local diffraction efficiency by changing the width and the number of levels in every period. To reduce complexity, an algorithm for designing the element with the least number of levels and masks is developed. This design algorithm determines the needed mask parameters in which compensation for distortions introduced by the lithographic recording of the element are taken into account. Calculated and experimental investigations that confirm the new design approach are presented.

A new electro-optic modulator is designed and constructed. It is suitable for maintaining modulation at a high frequency and can be used to generate ultra-wide-sideband signals to form ultrashort optical pulses. In experiments, phase modulation with a modulation index of 57 rad is successfully obtained at 16.25 GHz, and thereby optical sidebands extending over widths as wide as 1.85 THz are attained. The sidebands produced are broad enough to form subpicosecond pulses using the chirping-compression method.

We report on civil engineering applications of wavelength multiplexed optical fiber Bragg grating arrays directly produced on the draw tower for testing and surveying advanced structures and materials such as carbon fiber reinforced concrete elements and prestressing cables. We equipped a 6 X 0.9 X 0.5 m concrete beam, which was reinforced with carbon fiber reinforced epoxy laminates, and a 7-m long prestressing carbon fiber cable made of seven twisted strands, with optical fiber Bragg grating sensors. Static strains up to 8000 µm/m and dynamic strains up to 1200 µm/m were measured with a Michelson interferometer used as Fourier spectrometer with a resolution of about 10 µm/m for all sensors. Comparative measurements with electrical resistance strain gauges were in good agreement with the fiber optic results. We installed the fiber sensors in two different arrangements: some Bragg grating array elements measured local strain while others were applied in an extensometric configuration to measure moderate strain over a base length of 0.1 to 1 m.

A unique method for the construction and display of a 3-D holographic movie is developed. An animated film is produced by rotating a 3-D object in steps between successive holographic exposures. Strip holograms were made on 70-mm AGFA 8E75 Holotest roll film. Each hologram was about 11-mm high and 55-mm wide. The object was rotated 2 deg between successive exposures. A complete cycle of the object motion was recorded on 180 holograms using the lensless Fourier transform construction. The ends of the developed film were spliced together to produce a continuous loop. Although the film moves continuously on playback and there is no shutter, there is no flicker or image displacement because of the Fourier transform hologram construction, as predicted by the theoretical analysis. The movie can be viewed for an unlimited time because the object motion is cyclical and the film is continuous. The film is wide enough such that comfortable viewing with both eyes is possible, enhancing the 3-D effect. Viewers can stand comfortably away from the film since no viewing slit or aperture is necessary. Several people can simultaneously view the movie.

High resolution radiometric images of a large terrain were obtained by scanning the area with a downlooking imaging radiometer attached to a helicopter. A detailed description of the data acquisition process is presented. The output of this process was thousands of small images, which were then combined (mosaiced) to one large radiometric map. For the mosaicing process we use image registration algorithms developed especially for the case where the input images contain no significant features or contrasts, as might be expected from radiometric desert backgrounds at night. In this situation, traditional feature-based or intensity-based registration methods can give unsatisfactory results. We improve these methods using some heuristics. This enables the automatic mosaicing of a few thousand images in a very short time. An example of the use of the resulting radiometric map for the simulation of a thermal sensor searching for targets is described.

We propose a modification of the standard error-diffusion technique for image halftoning that enhances edges and textures by reducing the diffusion of the quantization error across edges. It employs a quadratic Volterra filter that extracts features from the original grayscale image and adapts the feedback loop to the local characteristics of the image. The additional computational complexity is small because the filter only uses a 3 X 3 region of support. Experimental comparisons of various techniques show that our modified error diffusion algorithm produces sharper results with improved contrast and detail resolution for both gray-scale and color images.

A simple method for adjusting pseudocolor distributions of photographic images is described and demonstrated experimentally. This method is based on the technique for photographic phase image pseudocolor modulated by a grating. A reflecting ray path is introduced into a 4f system to produce diffraction of the dual-phase grating so that the pseudocolor at the output plane can be adjusted. The merit of this method is that many pseudocolor images with different color distributions can be obtained for each diffraction order.

We compare several wavelet-based coders in the encoding of still images. Two image-quality metrics are used in our comparative study: a perception-based, quantitative picture quality scale and the conventional distortion measure, peak signal-to-noise ratio. Coders are evaluated in the rate-distortion sense. The effects of different wavelets, quantizers, and encoders are assessed individually. Two representative wavelets, three quantizers, three encoders, and the combinations of these components are compared. Our results provide insight into the design issues of optimizing wavelet coders, as well as a good reference for application developers to choose from an increasingly large family of wavelet coders for their applications.

An alternative to traditional spatiotemporal gradient and feature-based approaches to measuring object velocity in images is introduced. Here, the velocity is computed by treating each object as a distinct intensity wave profile, with Fourier components, and by identifying the Fourier components that exhibit the magnitude and phase changes that are consistent with anticipated velocity wave motion. This detection is accomplished using an appropriate Hough transform. The two major advantages of this technique are that because the analysis takes place in the Fourier domain, the spatial organization and the visual appearance of the moving object are not significant and, second, the formulation presented in this paper lends itself to direct extension for more complex motion. Consequently, objects that are visually or spatially complex and that would be difficult to analyze using either of the traditional spatiotemporal differentiation or feature-based approaches can be effectively treated. The proposed approach is demonstrated for scenes of varying complexity.

The optical multichannel transducer array (OMTA) is a fiber optic-based sensor designed to measure pressure profiles with high time and spatial resolution for wind tunnel applications. The OMTA is an integration of various state-of-the-art technologies and consists of two interchangeable sensor array heads (10 channels, 32 channels) and the associated fiber optics, a filter spectrometer with a 64-element detector array, diode lasers and their controllers, and a LabView-based software control system. The sensor head arrays are produced by anisotropic etching of masked silicon wafers to produce multiple independent elements. These arrays, having 10 and 32 individual, 0.81-mm2 elements and 1.1-mm center-to-center spacing, are designed for flush mounting in a hypersonic wind tunnel model. Laboratory calibration using dc and low-frequency pressure ramps showed that the measurable displacement resolution was approximately 0.01 µ, which corresponds in this configuration to 0.1 psi. The frequency response is approximately 50 kHz for 32 channels. The entire system is mounted on one laboratory rack for installation near a wind tunnel facility.

The time-division multiplexing of a polarization-insensitive fiber optic Michelson interferometric sensor (TDM-PIFOMI) using phasegenerated carrier (PGC) demodulation is presented. A new automatic gain control (AGC) process for the phase sensitivity normalization of each sensor in the TDM-PIFOMI system using the PGC demodulation is described and demonstrated. In the TDM-PIFOMI system, this process can eliminate effects including the fluctuation of the laser source intensity and the variation of the light pulse intensity distribution in all fibers. The advantage of the AGC process is to implement the process under the optimum condition of the PGC demodulation.

We describe the control of a pulsed laser for measuring harmonic vibrations with double-pulsed addition electronic speckle pattern interferometry (ESPI). The basic requirement is to synchronize the laser pulses both to a known position of the object vibration cycle (to obtain a stationary fringe pattern) and to a charge coupled device (CCD) camera (to obtain one double pulse per field.) It is shown theoretically and experimentally that at low object-vibration frequencies (typically < 500 Hz) these synchronization requirements can cause instabilities in the laser output. A synchronization scheme to overcome these problems is described and experimental results presented at several low objectvibration frequencies. Addition fringe visibility is improved in real-time with an electronic filter.

At present there is no common language for comparing two different light sources. Trying to quantify (or even to explain qualitatively) the difference in performance terms, for example, of an axial and a transverse filament, or a gas discharge tube and a light-emitting diode, or a gas lamp mantle and a laser, is like comparing apples and oranges. We have developed a concept for a common representation of these diverse kinds of light sources, without reference to any coordinate system or light generation process. Based on an expansion in spherical harmonics of an intensity data set over a sphere, we characterize the angular light distribution of a source by providing a prescription for calculating the orientation-independent parameters dl that represent the proportion of rms power distributed in each angular mode.

The goal of this work is to develop a general light source model that is physically accurate, intuitively descriptive, computationally convenient, and applicable to real sources. It solves two major problems in illumination optics: near zone general extended light source characterization for accurate image rendering and ray tracing, and computerautomated reflector design using the resulting near-zone model. The main approach is to combine measurements with Fourier analysis, using judiciously chosen coordinate systems and orthogonal fitting functions. This has several advantages over standard ray tracing: it provides for natural data compression and interpolation; it bypasses the problem of computing the radiance distribution of a real source by using actual pinhole CCD camera measurements; and it eliminates the computationally intensive ray-filament intersection problem by transforming the source into an equivalent nonuniform spherical radiator. A method for treating the occlusion of rays by the extended filament, with only spherical intersection calculations, is also discussed. The application of the method is illustrated by the problem of designing a smooth specular reflector to cast a desired intensity distribution on a distant screen for a given source. The problem becomes a straightforward numerical optimization of the perturbations to a base reflector shape. An algorithm to provide a first guess for the perturbations based on the shape of the image perimeter is also described.

We present a novel technique for measuring phase modulation in a liquid crystal television (LCTV) panel using the fractional-Talbot effect. We show that the phase modulation property in an LCTV can be obtained by measuring the contrast ratio of the Fresnel diffraction field at one quarter of the Talbot distance. We also generate a multilevel phase grating that produces a Talbot array illuminator to verify the experimental measurement result.

As the critical dimensions required in mask making and direct write by electron beam lithography become ever smaller, correction for proximity effects becomes increasingly important. Furthermore, the problem is beset by the fact that only a positive energy dose can be applied with an electron beam. We discuss techniques such as chopping and dose shifting, which have been proposed to meet the positivity requirement. An alternative approach is to treat proximity correction as an optimization problem. Two such methods, local area dose correction and optimization using a regularizer proportional to the informational entropy of the solution, are compared. A notable feature of the regularized proximity correction is the ability to correct for forward scattering by the generation of a ‘‘firewall’’ set back from the edge of a feature. As the forward scattering width increases, the firewall is set back farther from the feature edge. The regularized optimization algorithm is computationally time consuming using conventional techniques. However, the algorithm lends itself to a microelectronics integrated circuit coprocessor implementation, which could perform the optimization faster than even the fastest work stations. Scaling the circuit to larger number of pixels is best approached with a hybrid serial/parallel digital architecture that would correct for proximity effects over 108 pixels in about 1 h. This time can be reduced by simply adding additional coprocessors.

Silicon-compound optical coatings (silicon nitride, dioxide, oxynitrides) were prepared by plasma-enhanced chemical vapor deposition (PECVD) at near-ambient substrate temperature from SiH4/N2O/NH3 mixtures, using a dual-mode microwave/radiofrequency plasma system. The refractive index profile of the films was adjusted with depth in two ways: (1) between 1.45 (SiO2) and 1.90 (SiN1.3) by varying the N2O/NH3 feed gas ratio, and (2) between 1.65 and 1.90 for SiN1.3 films, by increasing the energy of bombarding ions from 5 eV to 400 eV. The film composition was changed either abruptly (multilayers) or continuously (graded-index, inhomogeneous layers). The resulting optical properties are correlated with the depth profile analysis of the chemical composition, and with mechanical characteristics such as adhesion, stress, and scratch resistance.

Most optical pattern recognition techniques rely on correlation that inherently achieves translation invariance. We introduce a significantly different formulation for image recognition in which a set of inner product operators are used to achieve translation-invariant pattern recognition. Our formulation extends the distortion-invariant linear phase coefficient composite filter family, developed by Hassebrook et al., into a set of translation-invariant inner product operators. Translation invariance is achieved by treating 2-D translation as distortion. The magnitudes of the inner product operations are insensitive to translation, whereas the phase responses vary, but are discarded. For large images containing many objects, this method can be applied by tiling the 2-D operators to the test image size, elementwise multiplying by the test image, and then convolving with a binary rectangular window. Impressive numerical efficiency, exceeding that of fast Fourier transform-based techniques, is attained by the inner product operator approach. Examples of our approach, distortion-invariant detection and discrimination capabilities, idealized optical implementation, and comparison with conventional matched filters are presented.

An optimum training process using a simulated annealing algorithm for synthesizing a spatial domain bipolar composite reference function (BCRF) is presented. The major advantages of the proposed BCRF filter are out-of-plane rotation invariance, higher discriminability (in particular, for similar targets), and convenience for optical implementation of a BCRF filter using a photorefractive (PR) crystal in a VanderLugt correlator is provided, in which we show that the experimental results agree with the simulation.

We propose a new segmenting method for handwritten Chinese signatures based on the wavelet transform for signature verification. There are some differences in identifying a handwritten signature and in recognizing a handwritten character because there are meaningful features hidden in writing habits when an individual is signing his or her signature. These features exhibit themselves in the pen-down, penup, and in the corner of a stroke. Therefore the segmentation for identifying a signature and for recognizing a character should be different even though the same characters are involved. We propose to segment an input signature curve at the inflection points, and we locate the inflection points by detecting the zero-crossing points of the wavelet transforms of the input signature. Experimental results show that this new segmenting method has better segmentation capability than other methods that are usually used.

A quick and efficient technique for automatic profilometric measurement of a large-form part is proposed and verified by experiment. When a laser stripe is projected onto an object, the deformed laser line image is detected by a solid-state array camera and automatically transferred to its space position using a least-squares mapping algorithm. Measurements can be executed on any surface of a 3-D object except the base. Large arrays of data points are acquired on each surface by means of a scanning mechanism. Since the measuring data from each laser stripe position can provide 2-D information concerning the surface contour, the laser stripe and the solid-state array camera are integrated into a measurement system for obtaining the entire 3-D information. Experimental results show that this technique can determine the 3-D profile of an object with an accuracy of 0.5 mm.

A method that employs an integrating sphere and a singlewavelength (1.6-µm) pyrometer for measuring the spectral effective emissivities of superalloys in the temperature range (~650 to 1050 °C) is described. The spectral effective emissivities for five superalloys, namely, MARM-247, MARM-509, CMSX-4, Inconel-718, and N-155 were measured. Correcting the pyrometer measurements for the variations in the object emissivity would reduce the uncertainty in the temperature measurements to < ± 1%.

A noncontact optical microtopographer based on an active, discrete triangulation procedure has been under development for some time at the physics department of the University of Minho. Our experience has shown that this kind of triangulation-based surface inspection system can be applied, not only to long-distance range sensing, but also to smaller samples or other surfaces with height resolutions that can go down to the submicron range. In our system, the topographic information is obtained from the horizontal shift of the bright spot created by an oblique collimated light beam on a surface when it is displaced vertically. A laser beam is focused onto a small, diffraction-limited spot on the surface and is made to scan it over the desired region. The horizontal position of the bright spot is perpendicularly imaged onto a linescan camera and the information on the individual detectors that are activated, above a certain controllable intensity threshold level, is used to compute the corresponding horizontal spot’s shift on the reference plane. Thus we can compute the distance between the surface and a reference plane at each sampled point. A map of the surface topography can then be built and statistical surface characterization parameters may be calculated. Our versatile laboratory setups have been used for different inspection tasks such as thickness measurements and relief mapping of different kinds of films (polyethylene, thin sputtered copper, tin dioxide and silver films) and several kinds of fabrics, and roughness measure and topographic inspection of polyethylene molds and graphite samples. In this communication we briefly describe our method. The current configuration of our laboratory setup is described. A hand-held version of our system and also the setup for long-distance dimensional assessments are briefly presented.

A method for reconstruction of an object f (x) x5(x ,y ,z ) from a limited set of cone-beam projection data has been developed. This method uses a modified form of convolution back-projection and projection onto convex sets (POCS) for handling the limited (or incomplete) data problem. In cone-beam tomography, one needs to have a complete geometry to completely reconstruct the original three-dimensional object. While complete geometries do exist, they are of little use in practical implementations. The most common trajectory used in practical scanners is circular, which is incomplete. It is, however, possible to recover some of the information of the original signal f (x) based on a priori knowledge of the nature of f (x). If this knowledge can be posed in a convex set framework, then POCS can be utilized. In this report, we utilize this a priori knowledge as convex set constraints to reconstruct f (x) using POCS. While we demonstrate the effectiveness of our algorithm for circular trajectories, it is essentially geometry independent and will be useful in any limited-view cone-beam reconstruction.

A method of modulation transfer function (MTF) measurement for charge-coupled device (CCD) focal-plane array (FPA) detectors that employs stochastic input in the form of laser speckle has been demonstrated with great success.1,2 This method, termed the ‘‘original method’’ henceforth, was recently improved upon3 by means of a hologram of speckle diffracted by an extended frequency aperture (EFA). Synopses of the two methods follow (the details are found in Refs. 2 and 3).

Confocal microscopy has advanced in the last five years in the areas of instrument development, theory, new fluorescent probes for ion imaging, and new applications. These advances are reflected in the increasing number of users of these instruments and their publications.