This PDF file contains the editorial “Why do we use keywords?” for OE Vol. 39 Issue 09

We report progress in the development of very lightweight (<5 kg/m2) mirrors made by replication using graphite fiber cyanate ester resin composites. The replication process is optimized to significantly improve the surface smoothness and figure quality. Achievements include near-diffraction-limited optical performance [<1/20 wave root mean square (rms) at 632.8 nm] in replica flats, fractional wave rms performance in curved mirrors at 90% pupil, and almost exact reproduction of the surface microroughness of the mandrel. The curved mirrors typically show some edge roll off and several waves (rms optical) of astigmatism, coma, and third-order spherical aberration. These are indications of thermal contraction in an inhomogeneous medium. The inhomogeneity is due to a systematic radial variation in density and fiber/ resin ratio induced in composite plies when draped around a small and highly curved mandrel. The figure accuracy is expected to improve with larger size optics and in mirrors with longer radii of curvature. Nevertheless, the present accuracy figure is sufficient for using postfiguring techniques such as ion milling to achieve diffraction-limited performance at optical and UV wavelengths. We demonstrate active figure control using a simple apparatus of low-mass, low-force actuators to correct astigmatism. The optimized replication technique is applied to the fabrication of a 0.6-m-diam mirror with an areal density of 3.2 kg/m2. Our result demonstrates that the very lightweight, large-aperture construction used in radio telescopes can now be applied to optical telescopes.

A Nd:Cr:GSGG concave-convex power oscillator was developed that utilized both an adaptive mirror comprised of spherical and cylindrical optical elements together with a Faraday rotator to dynamically eliminate lower order aberrations (thermal focusing, astigmatism, and bipolar focusing). An adaptively controlled collimating lens corrected for shifts in the mode-waist position. The addition of a polarizer and a reentrant mirror totally eliminated thermal birefringence losses. The techniques developed are attractive in any solid state laser that must work under changing pump power conditions.

Compact and all-fiber connectorized photonic delay-line modules based on three-dimensional bulk polarization optics are proposed and experimentally demonstrated. The modules are built on a single optical microbench and demonstrate optical leakage noise performance of ?40 dB at switching speeds of 10 ?s. Insertion loss analysis is also performed. A special gradient-index lens fiber optic collimator design is proposed to further reduce the optical insertion loss of the delay-line module. A wavelength-dependent design is also proposed for expanding the applicability of the PDL module to multichannel operation.

Our purpose is to develop a compact focus head for Nd:YAG laser processing in restricted spaces. The focusing assembly is a scaled- down "conventional" focus head with two conventional planoconvex focusing lenses and an outer diameter of 10 mm. Thermal and optical analyses are carried out to optimize the gas cooling design and the optical configuration of the focus head. Power capacity and processing tests confirm the capability of the focus head to produce good quality welds at powers up to 1400 W. Although extended life tests are not carried out, neither the head nor its optics show any signs of damage after approximately 40 min of processing.

We describe a simple device for fluorescence sensing based on an unexpansive light source, a dual photocell and a Watson bridge. The emission is detected from two fluorescent samples, one of which changes intensity in response to the analyte. The emission from these two samples is observed through two orthogonally oriented polarizers and an analyzer polarizer. The latter polarizer is rotated to yield equal intensities from both sides of the dual photocell, as determined by a zero voltage from the Watson bridge. Using this device, we are able to measure fluorescein concentration to an accuracy near 2% at 1 ?M fluorescein, and pH values accurate to ±0.02 pH units. We also use this approach with a UV hand lamp and a glucose-sensitive protein to measure glucose concentrations near 2 ?M to an accuracy of ±0.1 ?M. This approach requires only simple electronics, which can be battery powered. Additionally, the method is generic, and can be applied with any fluorescent sample that displays a change in intensity. one can imagine this approach being used to develop portable point-of-care clinical devices.

Background clutter characterization in infrared imagery has become an actively researched field, and several clutter models have been reported. These models attempt to evaluate the target detection and recognition probabilities that are characteristic of a certain scene when specific target and human visual perception features are known. The prior knowledge assumed and required by these models is a severe limitation. Furthermore, the attempt to model subjective and intricate mechanisms such as human perception with general mathematical formulas is controversial. In this paper, we introduce the idea of adaptive models that are dynamically derived from a set of examples by a supervised learning mechanism based on genetic programming foundations. A set of characteristic scene and target features with a demonstrated influence on the human visual perception mechanism is first extracted from the original images. Then, the correlations between these features and detection performance results obtained by visual observer tests on the same set of images are captured into models by a learning algorithm. The effectiveness of the adaptive modeling principle is discussed in the final part of the paper.

A new scheme for a still image encoder using vector quantization (VQ) is proposed. The new method classifies the block into a suitable class and predicts both the classification type and the index information. To achieve better performance, the encoder decomposes images into smooth and edge areas by a simple method. Then, it encodes the two kinds of region using different algorithms to promote the compression efficiency. Mean-removed VQ (MRVQ) with block sizes 8 x 8 and 16 x 16 pixels compress the smooth areas at high compression ratios. A predictive classification VQ (CVQ) with 32 classes is applied to the edge areas to reduce the bit rate further. The proposed prediction method achieves an accuracy ratio of about 50% when applied to the prediction of 32 edge classes. Simulation demonstrates its efficiency in terms of bit rate reduction and quality preservation. When the proposed encoding scheme is applied to compress the "Lena" image, it achieves the bit rate of 0.219 bpp with the peak SNR (PSNR) of 30.59 dB.

A stochastic image model is proposed for edge preserving smoothing. The derivation of the probability model for the first-order difference in the gray levels of the region pixels and edge pixels lead to a nonlinear filter with coefficients as functions of the estimated noise variance and edge intensity. Such a model-based approach enables the design of improved filters for noise filtering. Experimental results demonstrate the improved performance of the filter for both synthetic and natural images.

Fabric fuzziness refers to the severity of hairiness of a fabric caused by untangled fiber ends protruding from the surface, and indicates fabric deterioration in structure and appearance after repetitive abrasions in service. Although the average height and density of protruding fiber ends are the information that can be directly used to evaluate fuzziness, fiber ends are often too short and too fine to permit reliable measurements of fiber heights and density over a large area. In practice, visual examinations are often used for fuzziness evaluation despite the subjective nature of the method. An instrument that can perform reliable and quick evaluations of fuzzy appearance has been long demanded. This paper introduces the application of the wavelet transform to quantifying fabric fuzziness in a customized image analysis system. An index is constructed from the average powers of the components from different frequency bands, and is demonstrated to be indicative of fabric fuzziness.

we present theoretical analyses and computer simulations for incoherent imaging through a thin slab waveguide of length land slit opening 2a. Such an optical channel has a spatially varying point spread function, which introduces severe distortion. we show that phase diversity imaging, where the diversity is introduced by a simple spatial shift of the object, can significantly reduce the distortion. The spatial shift diversity is new to the literature. The results are shown with and without noise at 8-bit pixel quantization and are compared with the diffraction-limited image caused by imaging through the slit aperture alone.

Conventional infrared counter-countermeasure (IRCCM) techniques against flares in the rosette scanning infrared seeker (RSIS) are based on the image-processing algorithms such as the clustering and moment techniques. We analyze the conventional IRCCM techniques and find that they can handle only a limited number of clusters and may falsely recognize multiple targets as single ones. To overcome these limitations, we propose a new IRCCM technique using an iterative self-organizing data analysis algorithm. The proposed IRCCM classifies image clusters and calculates their centroids regardless of their numbers, since the ISODATA technique can handle an arbitrary number of clusters. The nonlinearity of the rosette pattern causes the calculated centroid of the target cluster to lean toward the middle of the pattern, i.e., the optical axis. For a precise determination of the cluster centroid, we also propose a new calculation method based on a weight function. We simulate the RSIS to evaluate the tracking performance in various situations. The simulation results prove that the proposed algorithm is very effective for IRCCM against flares.

We detected edges in noisy images using multiresolution analysis with the wavelet transform. products of wavelet coefficients at several scales were used to identify and locate edges. We found that it was important to consider the changes in edge position at different scales to detect edges in noisy imagery. We analyzed one-dimensional edges and compared the results of our approach with the first derivative of the signal. In addition, we compared the results of noisy images with another wavelet-based edge detection method. Our results led to improved edge detection in noisy images.

This paper presents an automatic map-based road detection algorithm for spaceborne synthetic aperture radar (SAR) images. Our goal is to find roads in a SAR image with subpixel accuracy with the help of a digital map. There are location errors between the digital map and the geocoded SAR image, which are about 20 to 30 pixels, and we adopt a coarse-to-fine strategy to reduce it. In the coarse matching step, we roughly find the locations of roads by a simple search using water areas or a generalized Hough transform based on digital map information. The fine matching step detects roads accurately by using the active contour model (snake). The input of the snake operation is the potential field constructed from the extracted ridges or ravines of curvilinear structures in the SAR image. Experimental results show that our algorithm detects roads with average error of less than one pixel.

A semidiscrete wavelet transform is realized using optical subband decomposition through which a signal is decomposed into translation-invariant subbands. Correspondingly, the translation parameter within each subband is discretized using a CCD array. since the sampling lattice of a CCD array is fixed, the subband signals can be oversampled, critically sampled, or undersampled. The oversampled subband signals contribute to reduced translation dependence and improved robustness. In the presence of additive noise, we show that oversampling reduces the reconstruction error.

We explain that a holographic filter of the generalized Hough transform can be easily obtained using multiplexing techniques in hologram recording. To show the feasibility of our approach experimentally, we record the Hough transform filter of both line and circle parameterizations by combined use of rotational and angle multiplexing. Preliminary experimental results on the Hough transform for a few input patterns are presented.

A polarization-encoding system for optical security verification is proposed. The polarization-encoded information can be used for secure verification. The polarization state of the input image can provide an additional degree of freedom in using optics to secure information. The expressions for polarization-encoded input images are developed using Jones polarization calculus. A nonlinear joint transform correlator is used to provide optical validation. Computer simulations and optical experimental results are shown in support of the proposed method.

A volume holographic wavelet correlation processor is proposed and constructed for correlation identification. It is based on the theory of wavelet transforms and the mechanism of angle-multiplexing volume holographic associative storage in a photorefractive crystal. High parallelism and discrimination are achieved with the system. Our research shows that cross-talk noise is significantly reduced with wavelet filtering preprocessing. Correlation outputs can be expanded from one dimension in a conventional system to two dimensions in our system. As a result, the parallelism is greatly enhanced. Furthermore, several advantages of wavelet transforms in improving the discrimination capability of the system are described. The conventional correlation between two images is replaced by wavelet correlation between main local features extracted by an appropriate wavelet filter, which provides a sharp peak with low sidelobes. Theoretical analysis and experimental results are both given to support our conclusions. its preliminary application to human-face recognition is studied.

In many applications such as in airborne and terrestrial reconnaissance, robotics, medical imaging, and machine vision systems, the images of a video sequence are severely distorted by vibrations. Superresolution algorithms are suitable for restoring an image from a lowfrequency vibrated sequence because of high correlation between the frames and inherent interframe motion. However, we show that superresolution algorithms, which were developed for general types of blur, should be adapted to the specific characteristics of low-frequency vibration blur. We demonstrate that in the case of image sequences distorted by vibration, the images should be selected prior to processing. We find empirical selection criteria and propose a selection procedure.

Current imaging system performance models use either the minimum resolvable temperature difference or the minimum resolvable contrast concepts to predict target identification performance. Both of these performance functions describe the limiting frequency that can be viewed through the imaging system at a particular contrast. No credit is given to the system for the amount of low frequency (lower than the limiting frequency) information that is passed through the system. We determine whether the low spatial frequency information is important in the target identification task. Previous experiments show that no degradation is seen on character recognition if a high-pass, edge enhancing filter is applied to character images. This is not the case in target identification performance, where the targets of interest are military tanks. A number of filters (six levels of blur at four bandwidth configurations) are applied to tank imagery including high-pass filters to reduce the low frequency image content. A perception experiment is performed to determine whether target identification performance was degraded with a reduced amount of low spatial frequency image content. The probability of target identification is calculated from the observer responses and the identification performance is evaluated as a function of low spatial frequency image content. Low frequency information is shown to contribute to the overall system performance.

A simple, fast and accurate light line technique for direct detection of 3-D shape is presented. This technique is proved by simulation and experimentally verified. To obtain the surface shape, the object is moved along an axis with an electromechanical device and scanned by a projected light line. Based on the measurement of displacement that suffers the projected line on the surface, object high data is obtained. Light line displacement is acquired by determining the precise position of its maximum on the object's surface and is compared with that projected on a reference plane. The described method has the advantages over conventional fringe pattern contouring that it is not necessary to design software to obtain the fringe phase and a phase-unwrapping step does not have to be applied. Another advantage is processing time, because the maximum is extracted using an efficient algorithm to fit a concave function with the light line intensity profile. The technique is quite skilled, robust, and highly accurate, and it can obtain the form of an object with complicated surfaces even with difficult details such as occlusions and discontinuities. Line light displacement can be obtained with resolution of fraction of a pixel, and a surface height accuracy up to 0.001 mm can be obtained.

Lateral migration radiography (LMR) employs scattered photons to acquire detailed images of covered objects. images of plastic encased real mines buried in soil using LMR have shown dramatic differences compared to images generated using simulated mines. The major characteristic that enables the discernibility of land mines to the degree of actual type identification is the presence of voids (air volumes) required for the operation of the fuse assembly or for blast direction control. Air volumes greatly modify the detected field of both once and multiple-scattered photons. The LMR system consists of an x-ray generator and two uncollimated detectors positioned to detect once- scattered photons and two collimated detectors designed to detect primarily multiple-scattered photons. The x-ray generator is located in the gap between symmetrically arranged detectors; the collimated x-ray beam typically has a spot size of 1.5x 1.5 cm with perpendicular incidence on the soil surface. The optimal x-ray spectra for land mine detection with the LMR system range from 130 to 180 kVp with mean x-ray energies of from around 40 to 60 keV. Air volumes modify both exit paths and the position of first-scatter events; they also modify the migration paths of multiple-scattered photons, thus producing different images in the two detector types. The burial mode (below surface or laid on the surface) of the land mine can also be discerned by LMR due to a shadowing effect seen for surfaced-laid land mines. The presence of even a minute amount of metal in the land mine also aids in discerning the mine, because metal produces a signal decrease in both types of detectors. Monte Carlo calculations are performed with the MCNp code to obtain an understanding of the details of the photon lateral migration process. Images generated from these Monte Carlo calculations are in agreement with the experimental measurements. The real mine images confirm that LMR is capable not only of mine detection, but also of mine identification.

The interference method for simultaneous measurement of the absolute refractive index and the thickness of plane parallel samples is developed. This method enables us to test solid (including optical glasses, crystals, plastics, and other sheet materials), liquid, and gaseous media over a wide spectral range. The experimental model for the realization of this method, the laser interference refractometer and thick- nessmeter (IRT), is manufactured and investigated. The IRT accuracy of the refractive index measurement is not worse than that of the best modern goniometers and the accuracy of the thickness measurement corresponds to the interference accuracy.

Electronic speckle-shearing pattern interferometry offers the possibility of analyzing out-of-plane and in-plane deformations in experimental mechanics. However, to obtain high-contrast fringes this technique must introduce large shears into the speckle patterns. Several techniques have recently been proposed to recover the phase from these data, but they all suffer limitations due to the slow convergence of the proposed algorithms or to the low precision of the recovered phase. This paper presents a least-squares estimation method in the frequency domain that allows wavefront recovery from two orthogonal shearing fringe patterns when a large shear is applied. This method is based on the application of a single Fourier filter using the fast Fourier transform process. The experimental results obtained by using electronic speckleshearing pattern interferometry for the analysis of a finite circular plate deformed at the center illustrate the advantages of the proposed technique.

We present a numerical comparison between shear-force, constant-height, and constant-intensity images in scanning near-field optical microscopy. We demonstrate the general difference between the three imaging modes. Two types of incident light are tested, with polarization perpendicular and parallel to the mean plane of the surface. Merits and demerits of the three images are discussed.

We present a new laser method that exploits curved-ray effects and that provides a practical method to investigate the stress profile in tempered glass. A feature of the technique is that the probing laser beam curves sufficiently that it exits on the same side as it enters; it does not reflect off or exit from the opposite side. The governing equations are formulated and studied using analytical methods and computer simulations. For a typical piece of tempered glass, the distance between the entry and exit points is of the order of a few tens of centimeters and is highly sensitive to details of the underlying stress distribution.

Some polarization properties of reflection-type photopolymer are investigated. The Mylar substrate alters an incoming linearly polarized laser beam to an elliptical polarization. The extinction ration is of the order of 1 to 3.7 for the tested samples. Polarization effects are found to change over different regions of each sample by approximately 10 to 50%. The Mylar substrate alone was found to distort the incoming polarization to a comparable degree. By aligning the position of the photopolymer to have the maximum amount of light passed through the analyzer, it is possible to make stabilized gratings with uniform diffraction efficiencies.

We describe a novel navigation sensor used for real-time navigation in which a position-sensitive detector is used. According to the features of the position-sensitive detector, the special floor mark stuck on the predefined path is developed. In addition, the formulas for the centroid position of the image of incident laser line on the position- sensitive detector, which is determined by the relative position between the floor mark and the navigation sensor, are derived. The navigation sensor, which can obtain proper navigation accuracy and controlling signal, navigates the autonomous guide vehicle running on the predefined path. It is suitable for application in autonomous guide vehicles and other automatic instruments. The experimental results are given.

Results of the (temperature) refractive index structure parameter (C2T), C2n, and the eddy dissipation rate e derived from the velocity structure parameter C2v are presented from fast response sensor observations using a kite/tethered-blimp platform in the Tularosa Basin at White Sands Missile Range, New Mexico, during the spring of 1998. Comparisons of different sensors (fine-wire probes and pitot tubes) measuring the same parameter are displayed and discussed while salient features of all sensors (standard and fast response) and the kite and tethered-blimp platforms are outlined. The nature and statistics of turbulence, including intermittency, under different stability conditions is discussed, including those found in the residual layer above the nocturnal boundary layer and the entrainment zone at the top of the daytime planetary boundary layer. In addition to displaying time series of temperature C2n and ? results obtained at specific altitudes and times, histograms of all daytime and nighttime C2n and ? values are compared to log-normal distributions. Examples of profiles of Cn2 and ? for daytime, near sunset, and nighttime conditions are shown and discussed. The relationship of Cn2 with ? is displayed for all data as well as sorted by daytime and nighttime. These results are explained in terms of potential and kinetic energy considerations under different atmospheric stability conditions.

The operation and performance of a 128-by-128 matrix electrically addressed ferroelectric liquid crystal (FLC) multiplexed transmissive spatial light modulator (SLM) and a 320-by-240 reflective silicon- backplane SLM are described. The two-dimensional multiplexed FLC SLM is probably the only device that exists to date optimized for ? = 1.55-?m operation. The spatial and temporal measurements of the binary phase modulation of the two devices are discussed. For the spatial measurements, a novel idea regarding the effects of the LC modulation characteristics in the interpixel deadspace of the silicon backplane on the quality of the binary phase modulation is described. For the temporal measurements, two addressing schemes for holographic beamsteering applications are described and compared experimentally with the silicon-backplane SLM. The limitation in performance for these two devices is briefly stated, and an indication given of future devices that will be possible using this rapidly advancing technology.

The accuracy of temperature measurement is the most important criterion for the evaluation of thermal cameras used in applications requiring absolute temperature measurement. All the main international metrological organizations currently propose a parameter called uncertainty as a measure of measurement accuracy. We propose a set of parameters for the characterization of thermal measurement cameras. It is shown that if these parameters are known, then it is possible to determine the uncertainty of temperature measurement due to only the internal errors of these cameras. Values of this uncertainty can be used as an objective criterion for comparisons of different thermal measurement cameras.

Several thermal models are introduced, based on both a steady-state and a non-steady-state heat balance equation. These are used to predict the surface temperature of dry bare desert background elements. Sensitivity analysis is performed for steady-state models, which indicates that for large measurement error the semiempirical models yield higher accuracy than the physical model. The non-steady-state models take account of variations of the meteorological parameters, and exhibit approximately 47% better performance for rapidly altering weather conditions. Also, the coefficients in these models may be used for a larger period of time to predict the surface temperature. Experimental tests are performed to examine the higher precision of the new models for predicting both the temperature and the thermal image of desert backgrounds. The mean prediction error of the new models is typically more than 25% better. Also, the contrast (variance) of the predicted thermal images is much closer to that of the real images during the daytime.

This paper describes a fast photometric stereo method, useful for the determination of surface-topography and reflectance. First we show how the irradiance in two images of a surface, illuminated from the left and right, respectively, can be used to determine the inclination of the surface elements. This requires a model for the light scattering properties of the surface. The model used divides the scattered light into a bulk-scattered, Lambertian part and a surface-scattered, specular part. The specular part is eliminated with the help of crossed polarizers. The inclinations are integrated to give a surface height function with the help of a Wiener filter, which suppresses frequencies with an expected poor signal-to-noise ratio. Profiles measured with this method show good agreement with profiles obtained both with optical and mechanical scanning methods. The standard deviation between surface height measured with the different methods was about 1 ?m. The ability of this method to study reflectance and topography at the same time makes it suitable for studies of the coupling between print result and surface topography. As an example, a gravure-printed paper surface with missing dots has been studied. It was found that missing dots occur at depressions, or pores, in the surface.

When a collimated beam of light is reflected by an approximately flat, mirror polished object and a screen is placed in the reflected beam some distance away from the object, a ‘‘magic mirror image’’ or Makyoh topogram of the object is formed on the screen. For objects with surface height variations, the topogram will not have a uniform intensity distribution, but even small height variations will show up strongly amplified as dark or bright patches/lines. Makyoh topography has been used for a number of years as a sensitive tool for the inspection of mirror polished surfaces, and in particular, semiconductor wafer surfaces. The main drawbacks of conventional Makyoh topography are, first, the ambiguity of interpretation because almost identical Makyoh topograms can result from an object with some given surface height profile and constant reflectivity, an object with constant surface height and a given nonuniform reflectivity profile, or an object with both height variations and a nonuniform reflectivity profile. The second drawback is the lack of quantitative interpretation, for example, surface height values cannot be obtained from the contrast in conventional topograms. I address these problems and describe a technique that for the first time enables the quantitative and unambiguous interpretation of Makyoh topograms.

To extract a precise target position in the presence of infrared countermeasures and significant noise, we propose a new algorithm based on the instantaneous frequency (IF) estimation of the sinusoidal frequency modulation (SFM) signals for a fixed-reticle seeker. To estimate the IF for target position extraction, the proposed algorithm maps the multicomponent sFm signal into the time-frequency plane to examine its time-frequency distribution, and then applies the Hough transform. The simulation results show that the proposed algorithm can extract the target position efficiently in the presence of flare countermeasures and noise.

A semiconductor laser speckle velocimeter that uses the selfmixing effect is studied for noninvasive relative blood flow measurements. The random modulation of intensity and spectra of the laser diode caused by the backcoupling of the scattered light from the red blood cells into the laser cavity is detected as a speckle signal with a photodiode inside the laser package. The autocorrelation of this self-mixing speckle signal gives information on the flow velocity of the blood. The proposed method is elucidated with in vitro and in vivo experiments. The results of these measurements are given together with a discussion of dependence of speckle signal of a self-mixing laser diode (SMLD) on various parameters such as velocity, hematocrit level of blood, and background reflectance of blood suspension.

In most applications of target detection electro-optical systems, the man-in-the-loop plays a crucial part in the performance of the system. If one were dealing with an automatic target acquisition system, a great deal of effort would justifiably be invested in calculating the threshold for determining a target for optimum system performance. When the system is human-operated, understanding the decisionmaking process of the human observer is of major importance to the successful performance of the system.