This PDF file contains the editorial “What’s Hot?” for OE Vol. 40 Issue 03

We deal with a novel proposal to obtain the curvature fringes by a quasi-real time technique incorporating the developed optodigital system for curvature measurement. An asymmetric Gaussian filter centered on the central frequency of the curvature fringes isolates the curvature fringes from the carrier shear fringes

We present a simple and efficient method capable of hiding a picture in two pictures, which we refer to as the picture hiding scheme. The proposed scheme generates two new pictures given two different original pictures and a secret picture. These two different original pictures are arbitrary, and the secret picture presents confidential information. The meanings of three pictures are not related to each other. An image defined as the secret picture can be recognized through the human visual system only when one of these two new pictures superposes on another new picture directly. This superposing process can be accomplished with two slides, therefore, no computation is performed. Anyone who obtains only one of these two new pictures cannot generate any knowledge of the secret picture. This picture hiding scheme can be used to construct a human identification scheme, which is particularly appropriate when delicate computer devices or instruments for identification are expensive. It also can apply to resolve the watermarking problem.

While interest in image and data fusion has grown significantly, its use in applications has been limited by the requirement that sensory data acquired from multiple sensors be accurately registered both spatially and over time. We present an autonomous stereo-based technique for spatially registering projective and range images acquired from externally uncalibrated sensors. Corresponding features are automatically extracted from range/projective image pairs. These points are then used to estimate the relative sensor pose by minimizing the difference between scanned and predicted stereoscopic range measurements. Experimental results obtained using a LIDAR scanner and a color camera are presented to demonstrate the accuracy of the stereo-based registration procedure.

We investigate the correlation characteristics of multiresolution image representations using compactly supported Daubechies wavelets. Subband correlation of two images consists of crosscorrelation of respective low-pass (approximation) and high-pass (detail) subbands generated from wavelet transform. Based on subband correlation, a fast algorithm for target localization and image registration is provided. In particular, a peak of approximation-subband correlation at a resolution level provides a guide for candidate location at the next finer resolution level, thereby confining the searching region and accelerating the matching. The presence of a sharp correlation peak in detail- subband correlation provides a precise location. Using N-order Daubechies wavelets with N= (1,2,3,4,5), the effects of the following aspects on subband correlation are investigated: (1) support length of wavelet filters, (2) random noises and static clutter, and (3) the in-plane rotation. Simulations show that approximation-subband correlation is relatively stable to random noises and static clutter whereas the detail- subband correlation is unstable to periodic translations, and the degradation of subband correlation is mainly attributable to the translation sensitivity.

Infrared thermography has been widely used to visualize a two-dimensional temperature field for various engineering applications. However, in general, conventional infrared thermography cannot directly be applied to quantitative temperature measurement on glossy metal surfaces under near-ambient conditions, because of the severe influence of the reflected energy incident from the surroundings on the measurement. When it is necessary to measure the temperature quantitatively, an appropriate calibration involving complicated procedures must be performed. In this paper, therefore, a new technique of measuring temperature is proposed for near-ambient conditions, by combining simultaneously several infrared radiometers having different detection wavelength bands to enable a two-color technique, which does not require any temperature calibrations. The sensors concerned have a selective wavelength band of several micrometers in width in the range of 2 to 13 ?m. The applicability of the method, including a series of proposed equations, has been confirmed by an investigation; the numerical simulation presented merely allows a parametric study of how the result varies for different values of emissivity corresponding to a pair of infrared radiometers. An experimental investigation is also performed to estimate or correct the measurement error pertaining to the present technique. This technique has the feature that a two-dimensional temperature field can be evaluated quantitatively, nondestructively, and simultaneously at each picture element without presuming any emissivity and reflectivity, even though the object has a complicated shape; so that it may be useful in various medical or engineering applications.

A technique is described for designing optical systems for generating interference signals in quadrature. This technique, which optimizes the amplitude and quadrature of the interference signals, is then used to optimize a phase quadrature interference system with minimal optical components and optical efficiency greater than standard systems.

A tandem white-light interferometer has been developed, based on the heterodyne technique, for highly accurate and sensitive surface profiling of a three-dimensional (3-D) object. Two acousto-optic modulators (AOMs) and two spherical reflecting mirrors are used in a Michelson interferometer to provide the optical frequency shift for white light. By using this technique in the tandem interferometer, the profiles of mirrorlike and diffusing surfaces of 3-D objects are measured with heterodyne signals of 200 kHz. The optical path difference of the interferometer can be stabilized by simultaneously using coherent and incoherent light. The experimental results show a 27-fold improvement in the stability of the interferometer and the possibility of achieving high accuracy of several tens of nanometers.

A differential absorption lidar system for measurement of trace atmospheric substances in the visible and UV regions is developed. The system is based on a pair of Nd:YAG pumped dye lasers, each capable of emitting two wavelengths on alternate shots. The measurement error of the system was evaluated by measurement of tropospheric O3 using two identical differential absorption lidar (DIAL) pairs, from which two null profiles and four DIAL profiles are obtained simultaneously. The null profiles, obtained for both the on and off wavelengths used in DIAL measurement, are useful to evaluate systematic DIAL measurement error due to beam misalignment. The null profiles show that this systematic error is at most 1.3%. The total DIAL measurement error is about 5%, most of which can be attributed to statistical error.

A prototype of a homodyne laser radar system for surface displacement monitoring using the reference beam technique is presented. The prototype is very simple, is easy to align and focus, and is able to measure the velocity of the surface displacement at distances up to 16 m. We present an optical analysis of the prototype, a power budget, a criterion on tolerance in distance and laboratory measurements.

An airborne lidar using commercial, off-the-shelf components was developed by the National Oceanic and Atmospheric Administration for fisheries' surveys. We make several test flights of the system and develop several signal processing techniques to discriminate between the returns from fish and from small particles in the water. We use these techniques to produce several products of use to fisheries' biologists. Examples are presented of gray-scale images similar to those produced by acoustic echo sounders, of maps of spatial distributions of fish, and of vertical profiles of fish biomass.

Flatbed scanners are increasingly used for scientific applications in which accurate determination of the scanner's illumination angle is often needed. A measurement method based on a dual-photodiode arrangement is proposed and demonstrated. The measurements obtained from experimental verification are found to be repeatable. The technique is also fast and easy to implement.

Gradient-index rod lenses have been developed and analyzed as imaging optical elements, but their capability as flux concentrators has not been explored. Both analytic methods and computer ray- trace simulations are used for a comprehensive evaluation of the concentration and efficiency of these rods. They appear to be well suited as concentrators for the distal end of laser fiber optic surgical units, toward improving surgical efficacy and reducing expensive laser power.

A system of small-rotation-angle measurement based on fringe projection is proposed and demonstrated. This system has potential for a broad range of uses and robustness to external disturbances, because it requires no coherent light. The setup is very simple and applicable to automatic on-line measurement. Several measurements indicate a sensitivity of 3 arcsec.

A new method for estimating the motion parameters of a target from its stepped-frequency inverse synthetic aperture radar signature is developed, implemented, and tested. The proposed method uses the phase of the target's echo transfer function to focus the radar image while avoiding Fourier processing. A focal-quality indicator is proposed that yields optimum motion-parameter estimates with the least number of computations. Complex analysis is exploited to measure the slope of the phase more accurately by selecting regions of the target signature with a high signal-to-noise ratio. A weighted-least-squares approach optimizes the estimation process by grading the selected segments and assigning reliability weights. The Cramer-Rao bounds for lower limits on velocity and acceleration estimates are derived in the context of weighted-least-squares complex analysis. The proposed method provides higher accuracy and efficiency than conventional methods.

With the increased interest and use of staring IR focal plane arrays, the characterization of fixed pattern noise in task performance is becoming more important. Past work includes theoretical treatments and laboratory measurements to describe the characteristics of fixed pattern noise on target acquisition performance. This is the first target acquisition experiment that describes the relative effects of fixed pattern noise and temporal noise on target identification. Static IR tank images are processed with six different levels of fixed pattern noise and six different levels of temporal noise. A perception experiment is performed where 10 U.S. Army soldiers were tasked to identify the tanks through the combinations of noise. Additive noise was applied in both Gaussian and uniform distributions. The results enable a direct comparison between the effects of fixed pattern noise and temporal noise on target identification.

We achieve a fast alignment of optical axes that must be precisely positioned with multiple degrees of freedom during coupling between optical devices using the Hamiltonian algorithm. The Hamiltonian algorithm utilizes the mixing properties of the dynamical system and can efficiently search for the global minimum of the objective function in an optimization problem. Simulations show the effects of the mixing for a quick search for the global minimum, avoidance of trapping at the local minima, and robustness against disturbance. Our experiments show that using this algorithm, optical axes with multiple degrees of freedom can be aligned efficiently and several fibers can be aligned simultaneously. Therefore, it is confirmed that the time for completing alignment of many optical axes is greatly reduced.

We describe a singly resonant optical parametric oscillator (OPO) using a noncritically phase-matched KTP crystal, intracavitypumped by a Q-switched Nd:YAG laser. Signal pulse energy of as much as 8.1 mJ in the eye-safe range at 1.58-?m wavelength was coupled out of the cavity. We have elaborated a simple model of an intracavity laserpumped OPO (IOPO), based on the rate equations for the Q-switched laser combined with the coupled equations for the parametric interaction in the nonlinear crystal. At 1.5 times pulsed IOPO threshold, signal pulse widths of 5 and 6 ns were calculated and detected, respectively.

Investigations are performed for threshold characteristics of 1.55 ?m InGaAs/InGaAsP strain-compensated quantum well lasers with zero net strain. The computed results show that certain relations exist among the well width, cavity length, intrinsic loss and facet reflectivity for realization of 1.55 ?m wavelength emission. These parameters affect the threshold gain, threshold carrier density and threshold current density. A minimum cavity length exists for a single quantum well laser, near which the threshold carrier density and threshold current density become very large.

The behavior of the temporal output profile for a double cavity Tm:YLF laser was investigated experimentally. In single-mode- longitudinal operation, the behavior of the periodic oscillation is found to be in good agreement with the theoretical analysis of the relaxation oscillation.

The as-deposited stress of typical high-reflectance extreme ultraviolet (EUV) Mo/Si multilayer mirrors is measured to be approximately ?410±10 MPa (compressive). These multilayers are deposited with dc magnetron sputtering and have near-normal incidence (5 deg) reflectances of 67.2±0.1% around 13.2 nm. The effect of both slow and rapid thermal treatments on multilayer stress and reflectance is measured. For both approaches, the stress of these multilayers is reduced quasi-linearly with the annealing temperature. Using the slow thermal anneal approach, it is possible to reduce the stress from ?410 MPa to zero by heating the sample to ~275°C with a corresponding reflectance loss of ~3.5% (absolute). If preserving the reflectance is critical, we show that heating the sample to ~220°C reduces the stress by 85% from ?407 to -63 MPa with a reflectance loss of only ~1.5% (absolute). It therefore appears possible to ‘‘tune’’ the stress of EUV Mo/Si multilayer mirrors with this postdeposition annealing technique and predict the loss in reflectance for any given desired final stress. Moreover, it seems that the relationship between the reflectance loss and the stress change does not depend on the type of thermal treatment, i.e., it is the same for both the slow and rapid thermal annealing techniques.

The accuracy of phase-measuring profilometry is greatly influenced by environmental light, especially outdoors. The errors caused by changes of the environmental light are analyzed, and some simulated fringe patterns are processed. A new calibration algorithm, which performs intensity background and fringe amplitude transformations, is proposed. Theoretical analysis and experimental results verify that the improved phase-measuring profilometry is insensitive to the change of environmental light.