This PDF file contains the editorial “The Left Drawer” for OE Vol. 40 Issue 12

The third-order nonlinear optical properties of the octa-octyloxy phthalocyanine free base were studied by Z-scan using 35-ps laser pulses at 532 nm in toluene. The nonlinear refractive index or the refractive cross section, and the excited singlet state absorption cross section were determined. The optical limiting performances at both nanosecond and picosecond time scales have been investigated. The results suggest that the octa-octyloxy phthalocyanine free base is promising for optical limiting materials.

Use of fractional moments of low order, recently proposed by Consortini and Rigal for investigating probability density functions in laser scintillation statistics through atmospheric turbulence, is here proposed for overcoming the saturation of the electronics due to low- dynamics acquisition systems. Paper 200438.

Atmospheric turbulence imposes a limit on the resolution attainable by large ground-based telescopes. In the visible, adaptive optics (AO) systems can only partially compensate turbulence-induced distortions. Hence, the light intensity at the telescope image plane is a random variable. In order to check the light intensity statistics we have developed an experimental setup that simulates simultaneously the atmosphere and the AO effects. Phase modulation is produced by LCDs extracted from a commercial projector. It is shown that experimental histograms of the light intensity at the image plane fit the theoretical Rician distribution.

The color interpolation scheme can play an important role in overcoming the physical limitation of CCD image sensors and in increasing the resolution of color signals, while most conventional approaches result in blurred edges and false color artifacts. We propose an improved edge-adaptive color interpolation scheme for a progressive scan CCD image sensor with an RGB color filter array. The proposed edge indicator function utilizes not only the within-channel correlation, but also the cross-channel correlation, and reflects the edge characteristics of an image adaptively. The color components unavailable at each channel are interpolated along the edge direction, not across the edges, so that aliasing artifacts are suppressed. Furthermore, we eliminate false color artifacts resulting from the color image formation model in the edge- adaptive color interpolation scheme by adopting the switching algorithm based on the color edge detection. Simulation results of the proposed algorithm indicate that the improved edge-adaptive color interpolation scheme produces results that are quantitatively better and visually more pleasing than those achieved by conventional approaches.

A prototype of a multiway fibre bundle connector for astronomical applications is described. The connector provides for connection and disconnection in the fiber trains that feed an astronomical spectrograph. It also provides the more important function of converting the focal ratio from f/2 to f/5 because f/2 is too fast either for good transmission of light along a substantial length of fiber or for the input to typical astronomical spectrographs. The fiber bundle connector consists of 100 coupling fibers. It works over the full 0.9- to 1.8-?m wavelength range, and the chromatic aberration is well corrected in the design. The design principle and the construction of the connector are discussed. The measured coupling efficiency is up to 88%. The coupling efficiency is compared with a theoretical estimate, and good agreement is achieved. Possible further improvement is discussed.

We propose a method for optimizing the process of iteratively binarizing digital amplitude holograms by utilizing the effect of adding energy to the reconstructed signal window from the hologram. For this purpose, we introduce a parameter called the energy factor and show that the performance of the iterative binarization process can be greatly enhanced if the value of the energy factor is properly chosen. Finally, we show that the optimal values of this energy factor can be estimated with an analytical function for different computational costs.

An autostereoscopic display system can provide users the great enjoyment of stereo visualization without the uncomfortable and inconvenient drawbacks of wearing stereo glasses or head-mounted displays. To render stereo video with respect to the user's viewpoints and to accurately project stereo video onto the user's eyes, the left and right eye positions of the user, who is allowed to move around freely, have to be obtained when the user is watching the autostereoscopic display. We present real-time tracking techniques that can efficiently provide the user's eye positions in images. These techniques comprise: 1. face detection by using multiple eigenspaces of various lighting conditions, 2. fast block matching for tracking four motion parameters (X and Y translation, scaling, and rotation) of the user's face, and 3. eye locating in the obtained face region. According to our implementation on a PC with a Pentium III 700 MHz CPU, the frame rate of the eye tracking process can achieve 30 Hz.

This paper presents a simple mathematical performance model of the human foveal vision system based on an extensive analysis of the Blackwell-McCready (BM) data set. It includes a closed-form equation, the (ABC)t law, that allows the analyst to predict the entire range of BM threshold data. Relationships are derived among the four fundamental parameters of foveal vision: target area A, background luminance B, threshold contrast C, and stimulus presentation time t. Hyperbolic-curve fits on log-log plots of the data lead to the well-known laws of Ricco, Blackwell, Weber and Fechner, and Bloch. This paper unifies important relationships associated with target and background scene parameters as they relate to the human foveal vision process. The process of detecting a BM target, using foveal vision, is reduced to the total temporal summation of light energy modified by a multiplicative energy ratio. A stochastic model of human observer performance is presented in terms of a cumulative Gaussian distribution, which is a function of the apparent and BM contrast threshold values.

A technique that approximates the output of the soft morphological operators is described. The soft operators can be viewed as a voting process across neighborhoods defined by the structuring element. Instead of processing all votes across a neighborhood, this approximation technique randomly samples elements in the neighborhood and uses these values as inputs to a two-state finite state machine, where the state of the machine corresponds to the output at a given pixel. When properly designed, the machines sample a small fraction of the neighborhood, obtain output that is 91 to 100% accurate at each pixel, and is one to two orders of magnitude faster than conventional algorithms. Experiments on binary textures and digits confirm the theoretical results.

We present full-scale calculations of highly p-type doped siGe heterojunction internal photoemission (Hip) detectors that operate in the mid-infrared (3- to 5-?m) range of wavelength. We explore the effects of including undoped spacer layers within the highly doped siGe wells, for which a systematic body of experimental data is available to us, and which demonstrates a substantial reduction in the dark current produced by these devices. We model the doping explicitly by means of a screened Coulomb potential, leading to a full description of the resultant impurity band, and compare our calculated optical line shapes with recent state-of-the-art molecular-beam epitaxy experiments. The variation of the optical response with well width, germanium concentration, spacer width and position, and doping concentration are all considered.

Integrated tunable narrow-linewidth wavelength filters based on TE-TM mode conversion require a high quality processing. The discussion is based on numerical simulations of typical technology-induced defects and on a comparison with experimental results. We show that uniformity of the LiNbO3 crystal growth currently limits the linewidth to about 0.6 nm for spectral filters operating at 1.55 ?m. Moreover, such a filter would require a technology with strict conditions of uniformity over several centimeters. The discussion is focused on electro-optic filters but the results can be extended to any device based on codirectional mode coupling, such as acousto-optic filters.

A method is proposed for the identification of primary aberrations with a single image of a lateral shearing interferogram of optical components, obtained from a monochromatic laser source, using a neural network. The neural network is used to illustrate the features of the sampled interferograms and identify the primary aberrations of the other interferograms by means of its excellence in interpolation and extrapolation. Analysis of the pattern is performed to find the proper features to teach the neural network in less time. Simulations are performed to verify the suggested method.

The Leendertz dual-beam symmetric illumination-normal observation arrangement is widely employed for real time evaluation of in-plane displacement components as well as surface shape. Instead of observing along the optical axis, we have examined the Leendertz arrangement by observing the scattered light along the direction of the illumination beams, and imaged it as two separate images onto the photo sensor of a CCD camera. The interferometer is a combination of two channels, each of which measures independently and simultaneously the information pertaining to either the in-plane displacement component of a deformation vector, or the surface relief variation of a three-dimensional object. In addition, a summary of possible measurements that can be carried out from the present arrangement is also highlighted. Experimental results using a four-frame phase shifting technique are illustrated.

High precision zero power gain measurements are used to demonstrate that the energy transfer sequence SiO*(b3?)+Na(3s2S) ?SiO(X1?+) 1 Na*(4d2D); Na*(4d2D) ? Na(3p2P)+hv(569 nm); Na*(4d2D)+hv(569 nm) ? Na(3p2P)+2hv(569 nm) represents a viable visible chemical laser amplifier candidate. Dual beam radiometry is used to advantage in a sensitive and stable measurement system, which provides correction for: 1. source intensity fluctuations, 2. variations in source spectral density, 3. variations in detector spectral response, and 4. gain variations in detector and amplification stages. Experiments are performed to determine the amplification of a probe beam at 569 nm by an extended path length (nominal gain length ~5 cm) reaction energy transfer zone. For these quantitative gain measurements, the stability of the probe signal sets a limit on the sensitivity of the measurement. Considerable effort was expended to insure equivalent path lengths for probe and reference beams to compensate for source output variations so that the reference signal possesses the same temporal behavior as the probe, and the probe and reference optical systems image the same portion of the source on the detector. A gain coefficient, conservatively estimated as 0.8 to 1.53X10-3 cm-1, was measured. Based on this result, a Rigrod analysis indicates an expected full laser cavity output power between one and ten watts.

High-power passive Q-switching and mode-locking operation regimes of diode end-pumped Nd:YAG, Nd:YVO4, and Nd:YAP active media, operating at a 1.34-?m wavelength are investigated with V3+:YAG crystal as the saturable absorber. The highest average power of 2.1 W results from a Nd:YVO4 crystal placed in a 70-mm-long linear cavity. The corresponding pulse peak power and width are 0.1 kW and 133 ns, respectively. Employing a Nd:YAP crystal and 35-mm cavity length, the highest peak power of ~2.8 kW results when the laser runs at a 6.5-kHz repetition rate for an average power of —0.4 W. A record of 79-xJ pulse energy results from a 64-mm-long resonator with Nd:YAG gain media, however, for a decreased average power of ~0.24 W and pulses of 40-ns width. The mode-locking operation regime is investigated in a Z-type cavity. The best results, namely, ~0.5 W average power with mode-locked envelope energy in excess of 30 ?J and mode- locked pulse energy of 0.7 ?J, are obtained from the Nd:YVO4 media. Trains of 1-?s-wide pulses with improved stability result from a 1.5-m- long designed cavity with KTP crystal applied for passive negative feedback. A numerical modeling that takes into account the short recovery time of V3+:YAG saturable absorber (~5 ns) and excited state absorption effect is used to analyze and obtain general rules for optimizing such lasers.

Measurements under varied conditions performed with a homodyne laser radar prototype for surface displacement monitoring are presented. They include constant and variable velocity measurements from both a disk and a belt target. in this manner, a methodology for estimating the probability of detection and the standard deviation of the complete system is proposed.

Some expressions for temperature distributions and thermal deformations of silicon, sapphire, and calcium fluoride window substrates at 1.315 ?m are derived in terms of Green's function methods. Profiles for temperature rise and thermal deformation as functions of laser power, irradiating time and cylindrical coordinates are given. The calculated results show that under conditions of irradiating by a 10-kW intense laser with Gaussian shape, maximum temperature rises in Al2O3, CaF2, and Si substrates are 5.6°C, 6.0°C, and 35°C, respectively. The amounts of thermal distortion in Al2O3, CaF2, and Si substrates is 0.28, 0.99, and 0.40 ?m, respectively. At the initial stage of substrate laser irradiation, the temperature rises and thermal deformation increases quickly. After about 2 s, the increments of the temperature and thermal deformation become small. The trend of thermal deformation versus the heating time is in relative agreement with our experiment.

The authors develop a new technique for continuous measurement of liquid level by an optosensor. The objectives are (i) to study the propagation of light from a light-emitting diode (LED) through a glass tube and (ii) based on this principle, to develop a continuous liquid level sensor. The attenuation of light from an LED through a glass tube with distance has been investigated and an empirical relation for it has been established. The result is applied to the detection of water level. The sensor comprises a hollow glass tube with a combined LED- photodetector assembly (the optosensor) and a light reflector inside the tube. The reflector floats on the liquid surface, and light emitted from the LED is detected after reflection from it. The detected light intensity varies with the distance between the optosensor and the reflector. The position of the float changes with the variation of the liquid level. The present level sensor can detect a change of liquid level at distances up to 80 cm with an accuracy of the order of 0.5 mm.

We present a sensitivity analysis and performance evaluation of a six-degree-of-freedom measurement system that uses a diffraction grating as a cooperative target. To design the measurement system, we require a theoretical analysis of performance, such as sensitivity of each sensing direction. The intensity distributions of the diffracted beams are calculated with the scalar diffraction theory and sensitivity of the measurement system is analyzed against the variations of design parameter values. Using the results of sensitivity analysis, we design the measurement system and evaluate its performance with resolution, measurement error, and crosstalk. The resolution is less than 0.2 ?m in translation and 0.5 arcsec in rotation. In experiments, measurement error and crosstalk between sensing channels are within ±0.5 ?m in translation and ±2 arcsec in rotation.

The optical reference profilometer is a coordinate measurement machine (CMM) configuration that utilizes a special optical referencing frame to provide a stable and accurate surface measurement. This referencing frame provides several mechanical advantages that make it possible to use lower precision mechanical components while still maintaining high measurement accuracy. The optical reference profilometer also provides reduced measurement sensitivity to thermal variations of the environment. By utilizing a superinvar metering rod network, this CMM system is essentially thermally insensitive to temperature changes of the order of 1°C. This special feature makes the optical reference profilometer functional at a high measurement accuracy level in an open laboratory environment.

The use of compact disc (CD) pickups as distance sensors in optical profilometry is a well-established practice. The novelty of our device is the use of the built-in objective lens-tracking actuator of the pickup to perform a 1-D beam scanning of the sample. The profilometer prototype presented in this paper is made up of a standalone sensor-actuator optical head that can be easily positioned on samples of complex shapes with every orientation and can be operated by a remote control system. When 2-D scanning is unnecessary or even impossible, as for surface quality inspection of bulky mechanical pieces, a device that uses a CD pickup as both the sensor and the actuator is cheaper, faster, lighter, more compact, and more versatile than standard object-scanning setups that use xy translation stages. A lateral scan range of 800 ?m and a vertical scan range of 160 ?m are achieved.

An effective algorithm for automatic cartridge identification is proposed. The ejector impression is used to calibrate the cartridge image. Features of the firing pin impression and the breach face impression are extracted using active snake and orientation analysis, respectively. These different features are then integrated to make a final decision by using a support vector machine. Experimental results illustrate the effectiveness of our algorithm.

A new technique is proposed to solve the simple binary signal-detection problem using a nonunity kernel time-frequency signal detector (GNKD). The GNKD is based on a Cohen time-frequency power spectrum, employing nonunity kernels only. This class of signal detectors includes the Choi-Williams detector (CWWD) and the recently proposed hyperbolic detector (HyD). This work extends the work done by Kumar and Carroll, who investigated the cross unity-kernel Wigner-Ville detector (CWD), which is a special case of the GNKD class. The discrete Moyal's formula for the nonunity kernel time-frequency distribution is derived. The performance of the GNKD is then compared to that of the CWD and the cross-correlator (CORR) detectors by calculating the signal-to-noise ratio (SNR) and the loss factor Q. The GNKD is shown to be better than both the CWD and the CORR with improvement in the SNR by a factor of ?2. The HyD can improve the SNR by about 18% compared to the CWWD. Detection of some practical nonstationary signals is also investigated to exemplify the proposed method.

We describe a nonparametric approach of dynamic thermography to the detection of buried antipersonnel (AP) mines. Dynamic thermography consists of processing temporal sequences of IR images taken from the same scene, submitted to either artificial or natural temperature variations. The aim is to obtain an image segmentation where mine and soil can be discriminated due to the different time evolution of their thermal properties. The proposed approach is rooted in a clustering stage performed by a chaotic neural network and provides the correct classification by analyzing very short image sequences, thus enabling a fast acquisition time. The effectiveness of the method is demonstrated on image sequences of plastic AP mines taken from realistic mine fields.

A method for sensing wavefronts is presented. The method is based on the resolution of the irradiance transport equation, which relates the irradiance distribution and the shape of the wavefront of a light beam propagating along a given direction. The method presents no restrictions in the locations of the measurement planes and incorporates an improved procedure to geometrically correct the acquired images to take into account the effect of ray deflection in the propagation of the irradiance distributions. With the proposed technique, we measure the wavefront at the exit pupil of a progressive addition lens and find good agreement with an alternative deflectometric method.

The ability to machine very small features in material has a wide range of applications in semiconductor microelectronics, such as laser dye etching of ICs. Femtosecond-pulse laser pulses have been shown to hold great potential for high-precision micromachining. The extremely short duration of a femtosecond pulse highly limits heat diffusion, resulting in clean and defect-free ablation, making highprecision micromachining achievable.