This PDF file contains the editorial “Selling on the Web” for OE Vol. 38 Issue 08

For force-actuated, thin facesheet mirrors, structural flexibility within the control bandwidth calls for a new approach to adaptive optics. Dynamic influence functions are used to characterize the influence of each actuator on the entire surface of a deformable mirror. A linearized model of atmospheric distortion is combined with these dynamic influence functions to produce a dynamic reconstructor for providing actuator inputs in response to wavefront sensor measurements. This dynamic reconstructor is recognized as an optimal-control problem. A hierarchic control scheme that seeks to emulate the quasistatic control approach that is generally used in adaptive optics is compared with the dynamic reconstruction technique. Although dynamic reconstruction requires somewhat more computational power to implement, it achieves better performance with less power usage, and is less sensitive to errors than the hierarchic technique because it incorporates a dynamic model of the deformable mirror.

The effects of atmospheric turbulence on optical system performance depend primarily on the refractive index structure parameter C2n and the inner scale ?0. A simple model for C2n and ?0 is described and experimentally tested. The model, based on the Monin-Obuhkov similarity theory, was developed by Thiermann and is valid in the atmospheric surface layer over land. The inputs to the model are standard meteorological parameters plus solar irradiance and parameters that characterize the local terrain. Model results are compared with measurements of C2n and ?0 made with a laser scintillometer at a height of 1.8 m. The performance of the model was found to be good during unstable daytime conditions.

The discrete sources method (DSM) is extended to investigate complete mathematical models for light scattering from various kinds of silicon wafers features. Computer simulations demonstrate the usefulness of the DSM for comparing scatter signals associated with different surface features. Wafer features such as contaminating particles, subsurface defects and pits are investigated.

We present an original method that enables real time automatic dimensional control of defects on metallic objects. The method is based on the theoretical and experimental study of light reflection mechanisms that can be seen as a function of the surface roughness and of the light source size. We show that it is possible to reconstruct the profile of an object from a single gray level image. An industrial application enables us to validate our results. Finally, an error computation fixes the limits of our method and enables us to better understand illumination problems.

Image analysis is an appropriate tool to characterize qualitatively and quantitatively the first stages of the mechanism of damage by corrosion. The extraction of relevant information according to time allows us to establish the kinetic behavior of the pit growth. We show the development of a method of image analysis using an industrial device following the pit growth in the course of time on rough machined specimens after different periods of immersion in chemically corrosive matter.

Several simple models based on the geometrical theory of diffraction have been developed to be used in automatic control diameter of wires by optical diffraction, within the range of 10–200 µm. The experimental diffraction patterns are analyzed by Kriging method in order to estimate with good accuracy the location and the uncertainty of each minimum. The best geometrical model is selected by statistical analysis taking into account the uncertainty of the minima. The chosen model is used for the automatic determination of the wire diameter in systems of inspection and control.

A new layered image transmission (LIT) design algorithm is presented. The algorithm allows various decoder devices with different resolution and rate requirements to share a common image encoder. The number of layers for the transmission as well as the resolution and the average rate associated with each layer can be determined from the requirements of the decoders. Based on the constraints for each layer, the successive approximation quantization scheme is used to encode images for transmission. In addition to LIT, the algorithm can also be used to design progressive image transmission (PIT) systems where image resolution during transmission can be controlled. Simulation results show that the new algorithm is very effective for constructing both LIT and PIT systems.

A derivative-free, two-dimensional equiangular fan-beam reconstruction formula for a noncircular scanning locus is derived under three practical conditions. The formula contains the same terms as the traditional formula, except that the constant source-to-origin distance is replaced by the source-to-origin distance as a function of the rotation angle. The correctness of this formula is tested in numerical simulation. The potential applications of the formula include fourth-generation CT, electron-beam Ct, SPECT, and x-ray microtomography.

A 3-D multicriterion automatic segmentation algorithm is developed to improve accuracy of delineation of pulmonary nodules on helical computed tomography (CT) images by removing their adjacent structures. The algorithm applies multiple gray-value thresholds to a nodule region of interest (ROi). At each threshold level, the nodule candidate in the ROi is automatically detected by labeling 3-D connected components, followed by a 3-D morphologic opening operation. Once the nodule candidate is found, its two specific parameters, gradient strength of the nodule surface and a 3-D shape compactness factor, can be computed. The optimal threshold can be determined by analyzing these parameters. Our experiments with in vivo nodules demonstrate the feasibility of employing this algorithm to improve the accuracy of nodule delineation, especially for small nodules less than 1 cm in diameter. This discloses the potential of the algorithm for accurate characterizations of nodules (e.g., volume, change in volume over time) at an early stage, which can help to provide valuable guidance for further clinical management.

While high-resolution images are required for various applications, aliased low-resolution images are only available due to the physical limitations of sensors. We propose an algorithm to reconstruct a high- resolution image from multiple aliased low-resolution images, which is based on the generalized deconvolution technique. The conventional approaches are based on the discrete Fourier transform (DFT) since the aliasing effect is easily analyzed in the frequency domain. However, the useful solution may not be available in many cases, i.e., the underdetermined cases or the insufficient subpixel information cases. To compensate for such ill-posedness, the generalized regularization is adopted in the spatial domain. Furthermore, the usage of the discrete cosine transform (DCT) instead of the DFT leads to a computationally efficient reconstruction algorithm. The validity of the proposed algorithm is both theoretically and experimentally demonstrated. It is also shown that the artifact caused by inaccurate motion information is reduced by regularization.

A new general algorithm for phase-stepping interferometry is presented. The calculation of the phase distribution is composed of three least-squares fitting procedures for an analysis of real interferograms. First, we calculate the initial phase distribution utilizing Lissajous figures and elliptic least-squares fitting. Second, we calculate the phase steps through the spatial least-squares fitting. Finally, we calculate the exact phase distribution through the serial least-squares fitting. Both insensitivity to phase-step errors and automatic calibration of phase steps for the new algorithm are confirmed by experiment.

The comparison of two methods for determining the residual nonlinearity of the dual-frequency interferometer that has resolution of the order of a nanometer is presented. The first method estimates the maximum residual nonlinearity by determining the visibility of the measurement signal. This method has the advantages of easy operation and high resistance to environmental influence. The other method is high- precision calibration with another interferometer. To verify these two methods, a compact differential dual-frequency interferometer (DDFI) was set up and calibrated with a Fabry-Perot interferometer of China National Institute of Metrology (CNIM). The residual nonlinearity was estimated as 1.4 nm using the first method and 2 nm using the second. These two results fit well in spite of environmental influence.

Theoretical and experimental results for evaluation of 3-D shapes using light-in-flight speckle interferometry are described. Light- in-flight is a technique that uses laser light sources that emit ultrashort pulses or have a narrow coherence length. The interferogram of the object under study is only registered for the object parts for which the difference in path length between the reference and the object beam is less than the coherence length. Here, electronic speckle pattern interferometry for out-of-plane displacements is used to record the interferogram. An automatic evaluation system that consists of a computer- controlled image-processing system combined with a positioning system has been built to read the different contour lines and transform them into spatial coordinates, thereby detecting the three-dimensional shapes.

A 300-mm-aperture digital phase-shifting Fizeau interferometer (LADI) has been developed in house for precision metrology of optical components fabricated by the Optical Workshop at CSIRO Division of Telecommunications and Industrial Physics. This paper describes the optical and mechanical configuration of the instrument as well as its calibration and performance characteristics. Recent measurements on 250-mm-diam uncoated optical surfaces have consistently shown shortterm repeatability of 0.3 nm rms from measurement to measurement and allowed absolute characterization of these surfaces to an accuracy of a few nanometers.

We fabricate scanning near-field optical microscope (IR- SNOM) probe tips made from singlemode chalcogenide fiber and test them using a standard SNOM setup and free-electron laser. SEM micrographs, showing tips with submicrometer physical dimensions, demonstrate the feasibility of the thermal micropipette puller process used to create the tips. Topographical data obtained using a shear-force nearfield microscope exhibit spatial resolution in the range of 80 to 100 nm. Optical data in the IR (near 3.5 µm), using the probe tips in collection mode, indicate an optical spatial resolution of approximately ?/15.

The effects of conical optical channel parameters on divergence of the rays radiated from an emitter plate are investigated. The optical channel is used to maximize the radiant power (flux) in a given solid angle at the exit aperture of the channel. A simulation method is presented for optimizing the channel layout, using channel gain (efficiency) as a measure of the output radiant power. The Monte Carlo method is employed to generate emitted rays, and ray tracing is performed in a 3-D fashion using each of the three reflection models, i.e., specular, diffuse, and Gaussian. The simulation results indicate that, for a given solid angle of output radiation, the channel gain attains a maximum for certain values of length, cone angle and two radii of the semiconical channel. Moreover, the channel length has only a scaling effect on channel gain when the cone angle and ratio of two radii are constant.

A compact dynamic crossbar switch, based on a planar optics configuration, is presented. It consists of a pair of identical planar holographic cylindrical telescopes, each recorded on a single substrate, and a two-dimensional array (8x8) ferroelectric liquid crystal spatial light modulator. The crossbar switch can direct the light from any particular source in a one-dimensional array of 8 sources to a particular detector in a one-dimensional array of 8 detectors. The design of the overall configuration is presented along with experimental results.

We present a concept to modulate all three polarized Stokes components Q, U and V using two standard ?/2 ferroelectric liquid- crystal modulators. Thereby the complete Stokes vector (two linear polarizations and circular polarization) can be deduced from four intensity measurements taken at different phase intervals of the modulation. With ferroelectric liquid crystals, modulation frequencies in the kilohertz range are easily possible, which is necessary for applications in solar astronomy to overcome the influence of turbulence in the earth's atmosphere (seeing). No moving parts that could introduce spurious optical effects are used. In combination with fast demodulators, high-precision vector polarimetry in the visible can be performed. In contrast to conventional modulation schemes using one ?/2 and one ?/4 variable retarder, the technique presented here allows higher polarimetric efficiency and accuracy over a broad spectral range. A theoretical description is presented and compared with first test results on the system's performance.

Based on measuring the contrast of moire fringes produced by digital subtraction, an alternative method for object positioning is presented. We use a model of fringe visibility mismatch due to defocusing and search for a global maximum as the best focusing criterion. Both laser and white light illumination are tested. Experimental results shows an accuracy of 0.5 mm.

Satellite observations of agricultural and other plant canopies in the thermal and near iR regime have generally been at spatial scales of tens to hundreds of meters. Advances in sensor technology will extend our capabilities for IR measurements from space to yield improved spatial resolutions. We explore the variability in brightness temperature and the covariation of the normalized difference vegetation index (NDVI) with brightness temperature as a function of viewing geometry and changing spatial resolution. Using 3-D models for both canopy reflectance and thermal infrared exitance, we employ a theoretical analysis for an agricultural scene. The directional viewing effects and correlation between the NDVI and brightness temperature are found to be scale independent and in agreement with experiment. Directional anisotropy in brightness temperature and NDVI are calculated to be less than 7 to 12% respectively for zenith view angles less than 30 deg, but range up to 22 to 40% for zenith view angles of 60 deg. Analysis of variation in local standard deviations with spatial resolution shows a maximum peak corresponding to crop row spacing with rapid fall-off at larger scales.

Quantum-well infrared photodetectors (QWIPs) have potential applicability in many remote-sensing applications, even in the space environment where low background fluxes are involved. In this environment, the detector arrays may need to be operated at temperatures lower than 77 K. At these temperatures, tunneling mechanisms such as Fowler-Nordheim and trap-assisted tunneling could dominate the dark current. The device resistance, which is bias-dependent, increases by several orders of magnitude at these temperatures and may pose a problem. We have seen offsets in the current-versus-voltage (I-V) characteristics (nonzero current at zero bias not associated with dopant migration) which could impair the compatibility of a QWIP array with a readout circuit. We propose that these offsets are due to an RC time- constant effect. We further propose that the resistance in this time constant is due to tunneling mechanisms (and not due to contact resistance), which in turn are structure- and bias-dependent. We discuss our observations and present a circuit model of a QWIP that explains these observations nearly completely.

We address the problem of the way in which different, wellknown and commonly used image enhancement techniques effect qualitative human image judgments, and quantitative target detection performance. Two different psychophysical experiments are specially designed and performed to show how smoothing, full dynamic range exploitation, contrast and edge enhancement affect human abilities regarding target detection in IR imagery, and how this effect varies with imaging time and target thermal condition. Analysis of results shows systematic dependence on enhancement methods, very good agreement between image quality judgments and both target detection rates and probabilities. Significant interaction between enhancement methods and the time of day when the image is taken is also found.