This PDF file contains the editorial “Editorial: Scholarly Publishing” for OE Vol. 33 Issue 05

This PDF file contains the editorial “Guest Editorial: Semiconductor Infrared Detectors” for OE Vol. 33 Issue 05

Recent efforts in semiconductor IR detector research have been directed toward improving the performance of single-element devices,large electronically scanned arrays, and higher operating temperature. Another important aim is to make IR detectors cheaper and more convenient to use. New trends in semiconductor IR detector technologies are discussed, including HgCdTe photodiodes, Schottky-barrier photoemissive devices, alternatives to HgCdTe ternary alloys, monolithic lead-chalcogenide photodiodes, GaAs/AlGaAs intersubband quantum well photoconductors, and ways to improve the performance of nearroom-temperature detectors. A comparison of different types of detectors with the present stage of HgCdTe technology achievements is undertaken.

The major drawback of IR photodetectors is the need for cooling to suppress thermal generation of free carriers resulting in noise. New ways to improve the performance of infrared photodetectors operated without cryogenical cooling are discussed, including the optimum design of the devices, the use of optical immersion of photodetectors to high refraction index lenses, and the optical resonant cavity. Another and very promising way, however, is the suppression of thermal generation, which is governed by the Auger mechanism by depletion of the semiconductor in charge carriers. The stationary depletion can be achieved by the use of exclusion, extraction, and magnetoconcentration effects. The combination of various methods would eventually enable us to achieve near-background-limited photodetection (near-BLIP) performance of IR detectors without cooling.

We present p-on-n heterostructure HgCdTe photovoltaic device data that illustrate the high performance and flexibility in band-gap control of molecular beam epitaxy technology. This flexibility demonstration was performed by growing material for operation in the following cutoff wavelength (λ_co) ranges of interest: long wavelength IR (LWIR) [λ_co(77 K) = 9 to 11 μm], mid-long wavelength IR (MLWIR) [λ_co(77 K) = 6.8 μm], and very long wavelength IR (VLWIR) [λ_co(40 K)=20 μm]. Detailed analyses of the current-voltage characteristics of these diodes as a function of temperature show that their dark currents are diffusion limited down to 80, 50, and 30 K for the MLWIR, LWIR, and VLWIR photodiodes, respectively. In general, the R₀A device values were uniform for the three band-gap ranges when operating under diffusionlimited conditions. We confirmed this by fabricating a 64 x 64 LWIR (λ_co = 10.2 μm) hybrid FPA with detectivity (D*) operability greater than 97% when operating at 77 K. The mean D* value for this device was 1.4 x 10¹¹ cm Hz^1/2/W and it was background limited at the tested flux of 2.18 x 10¹⁶ photons/cm² s. This device was tested at higher temperatures of operation without changing background conditions, and it remained background limited up to 100 K.

The 1/f fluctuations of dark-current- and photocurrent-induced noise in implanted n⁺p Hg_0.5Cd_0.5Te photodiodes are analyzed within the diffusion-current-dominated bias region at 300 K. The lifetime of the electrons in the p-type region has been determined experimentally. Therefore, the Hooge parameter a_H is well defined by the 1/f noise spectrum. The a_H value, calculated from dark-current-induced 1/f noise, is in close agreement with the result of Handel's coherent state 1/f-noise theory, which yields a_H = 4.6 x 10^-3. The 1/f noise of the photoinduced current without applied bias can be described with the same a_H value. These results indicate coherent state quantum 1/f noise generated by dark current as well as photoinduced current as a result of mobility fluctuations. If both independent types of currents are generated in the photodiode, the resulting 1/f noise can be sufficiently described only within the concept of coherent state quantum 1/f noise.

The performance of thermoelectrically cooled p⁺ -n medium-wavelength infrared (MWIR) HgCdTe photodiodes is analyzed. The effect of doping profile on the photodiode parameters (R₀A product, quantum efficiency) is solved by forward-condition steady-state analysis. Results of calculations are compared with experimental data. The p⁺ -n homojunctions are formed by arsenic diffusion in HgCdTe epilayers. MWIR photodiodes effectively operate at elevated temperatures around 200 K and exhibit background-limited photodetection (BLIP) performance when monolithic optical immersion is used.

MBE growth and infrared device fabrication with epitaxial IV-VI layers on Si substrates are reviewed. Epitaxy on Si substrates is achieved using a stacked BaF₂/CaF₂ or CaF₂ buffer layer. With buffers containing no BaF₂, standard photolithographic delineation with wet-etching techniques can be used. Photovoltaic IV-VI sensors with cutoff wavelengths ranging from 3 to 14 μm are fabricated in PbS, PbSe_1-xS_x, PbEu_1-xSe_x, PbTe, or Pb_1-xSn_xSe layers on Si (111) substrates. They offer the possibility for low-cost infrared focal plane arrays with sensitivities similar to Hg_1-xCd_xTe, but with much less demanding material processing steps. A 13-mm-long linear array with 10.5-μm cutoff wavelength has inhomogeneities in cutoff below 0.1 μm. Some arrays were grown on prefabricated active Si substrates containing the whole readout circuits. First thermal images using these chips are demonstrated. The induced mechanical strain resulting from the different thermal expansion of IV-VIs and Si relaxes down to cryogenic temperatures even after many temperature cycles because of dislocation glide in the main {100} glide planes.

Temperature dependencies of dark electrical characteristics (Hall effect and conductivity) are investigated in PbSe polycrystalline films with different crystallite sizes deposited on glass and Si substrates. In these films the spectral dependencies of photoelectrical characteristics and the lifetime of photoexcited carriers on the crystallite sizes are studied. It is shown that the experimental data may be explained by the existence of the potential barriers for the majority carriers (holes) at the grain boundaries. The height of the barriers is found to depend on the crystallite sizes. PbSe photosensitive structures with detectivity D^*λ = 2 x 10¹⁰ cm Hz^½/W at room temperatures are fabricated on glass substrates. On Si substrates, the detectivity values of PbSe polycrystalline photodetectors were an order lower.

An improved 512 x 512-element PtSi Schottky-barrier IR image sensor (512 x 512 IRCSD) has been developed using the charge sweep device (CSD) readout architecture and 1.2-μm minimum design rules. Finer pattern process technology enhances the advantage of the CSD readout architecture, enlarging the fill factor without sacrificing the saturation signal level. A large fill factor of 71% is achieved in spite of a small pixel size of 26 x 20 μm². At the Schottky-barrier detector reset voltage of 4 V, the differential temperature response with f/1.2 optics at 300 K and saturation signal level were 3.2 x 10⁴ electrons/K and 2.9 x 10⁶ electrons, respectively. The noise equivalent temperature difference was estimated as 0.033 K with f/1.2 optics at 300 K. The improved 512 x 512 IRCSD was designed to be operated either in the field or frame integration interlace modes for versatility.

The current status of GaAs quantum well intersubband infrared photodetectors are presented by briefly reviewing some examples of the detector structures and their characteristics. The uniqueness of this new approach to infrared detection is painted out by presenting the multicolor and high-speed capabilities.

The study of intersubband transitions in both quantum wells and superlattices has rapidly developed to the point where intersubband photodetectors are becoming attractive for a number of applications. This is particularly significant for Si-based heterostructures due to the advantage of monolithic integration with the conventional silicon signal processing electronics, especially for large-area staring FPAs in advanced IR sensor systems. We review experimental observations of hole intersubband transitions in SiGe/Si quantum wells. In addition to intersubband transitions, we also discuss two normal incident absorption processes: intervalence band transition and internal photoemission from 2-D hole gas in the quantum well. Finally, the progress in the application of SiGe/Si multiple quantum well structures for the fabrication of IR detectors operating in both the 2- to 5-μm and 8- to 12-μm ranges is described.

Investigations of the performance of GaAs/AIGaAs quantum well IR photoconductors (QWIPs) as compared to HgCdTe photodiodes operated at temperatures below 77 K in the long-wavelength IR (LWIR) region are presented. In comparative studies, the current standard n⁺ -p HgCdTe photodiodes as well as p⁺ -n photodiodes are considered. Investigations of the fundamental physical limitations of HgCdTe photodiodes indicate better performance of this type of detector in comparison with QWIPs operated in the range 40 to 77 K. At 40 K, QWIPs with a cutoff wavelength of about 8 μm indicate higher detectivity. The advantage of QWIPs increases in wider spectral regions and at temperatures below 40 K. Usually, in the temperature range below 50 K the performance of n⁺ -p HgCdTe photodiodes is determined by trap-assisted tunneling. As a result, the advantage of GaAs/AIGaAs QWIPs increases in wider spectral regions (λ ≈ 8 to 12 μm) and at temperatures below 50 K. The comparison with p⁺ -n HgCdTe photodiodes is more complicated for lack of precisely modeled current transport in these junctions. GaAs/AIGaAs QWIPs at 40 K are background limited in low-background conditions. This observation plus the maturity of GaAs/AIGaAs technology and its radiation hardness characteristics promise that QWIP technology can produce high-quality focal plane arrays for space applications.

The operation of low-background lR extrinsic photoconductor detectors and detector arrays is essentially dependent on the process of spreading time-dependent photocurrent, which is due to low non-steady-state screening of the electric charges in the detectors. The spreading leads to an increase in the photoresponse time, an essential difference between the non-steady-state photocurrents in the circuits of the source contacts injecting free-charge carriers into the detectors and those in the circuits of the contacts that serve as drains for the carriers, and a high non-steady-state cross talk in the detector arrays. The results of the experimental study of all these effects and some others in 36- and 48-element linear arrays (Si:Ga) as well as their theoretical description are presented. The theory developed is in satisfactory agreement with the experimental data. Some consequences of the results obtained, which are important in space-based astronomy applications of such detectors, are discussed.

Doped silicon and germanium are used as extrinsic photoconductors for IR astronomy from ground-based, balloon-, and airborne observatories and from space platforms. The detectors of the Infrared Space Observatory (ISO) will be capable of observing at the sensitivity limits imposed by natural sky background radiation. For the first time, ISO will use stressed Ge:Ga detectors on a satellite covering the wavelength range out to 240 μm. Preflight testing has shown that ISO's calibration will have to correct for high-energy radiation effects and delayed flux response of its detectors. For future far-IR projects, these problems might be solved by blocked-impurity-band detectors. Several other difficulties in today's detector assembly production and readout technology also deserve improvements.

Formulae describing the spatial distribution of radiation intensity in a semiconductor film in a multilayer structure are given for the case of non-normal incidence of radiation. Interference of radiation internally reflected in such a sample makes the radiation intensity very sensitive to geometrical and material parameters of the structure as well as to the wavelength, angle of incidence, and polarization of radiation. The influence of radiation wavelength range and uncertainties of film thickness and refractive index on the spatial distribution of radiation intensity is discussed. The case of a graded-gap semiconductor film is analyzed. The presented formulae are useful in photoelectric and photoelectromagnetic investigations of thin film semiconductors and are also useful for the optimization of photon detectors.

This PDF file contains the editorial “Guest Editorial: Optical Interconnects and Packaging” for OE Vol. 33 Issue 05

The hardware and power requirements for a large asynchronous transfer mode packet switch that is implemented using several different mixes of optical and electronic (metallic) interconnections are studied. The optical interconnections are based on free-space digital optics, and the metallic interconnections are based on state-of-the-art electronic packaging technologies. The advantages and disadvantages of each of the different interconnection technologies are explored. These results should help researchers identify the areas that require improvement within each of the technologies. They should also be useful to designers of future systems who must select an appropriate interconnection and packaging technology.

A critical element in building parallel computers that use very fast processing elements is interprocessor communication. To utilize the processing elements efficiently, the interconnects in such parallel computers must provide high data rates and low latencies with extremely high reliability, compactness, and reasonable cost. We discuss the application of free-space optical links for interprocessor communication in parallel computers. Free-space transmitter and receiver modules have been fabricated and installed in a card cage enclosure. Repeatable signal levels have been achieved, after board removal and replacement, without the use of any micropositioners or adjustments. A time-division-multiplexed (TDM) ring network using high-speed (1 Gbit/s), point-to-point, free-space links has been designed to provide full connectivity among a set of processors connected to the ring nodes. Work is under way to demonstrate the 1DM ring network concept in a multiprocessor computer.

We discuss the potential of using free-space optical methods to implement a class of connectivity-enhanced mesh-based networks. As shown, the unique advantages that the free-space optics can offer, including large power fan-out per node capability, and the ability for spatial-angular multiplexing make it possible for connectivity-enhanced mesh-based networks to be efficiently implemented. In our presentation, two switching models, one for nonblocking point-to-point switching and the other for nonblocking broadcast switching, are described for their optical implementations. Some proof-of-principle experimental results are presented.

Linear polarization rotation tilt is a form of polarization aberration present in polarizing beamsplitter cubes when they are used in imaging systems. It is caused by the rotation of the polarizing axis (defined by the plane of incidence at the beamsplitting interface) for off-axis angles of incidence. This aberration is inherent to the geometry of the cube and is unavoidable, causing beam-routing errors and undesirable losses. In systems that use two or more polarizing beamsplitter cubes in succession, the cubes can be oriented to either minimize or maximize the loss, where the maximum loss is five times the minimum loss. This polarization aberration is described and a way to minimize beam-routing errors associated with this aberration in a 4-F optical system is demonstrated.

Refractive and diffractive micro-optics are combined in monolithically fabricated array components for free-space permutation interconnects. Such space-variant optical interconnects are, e.g., of major importance for smart pixel architectures, which are proposed for photonic switching applications in telecommunication and data communication and for more general parallel information processing, for example, of images. The advantages of the considered optical concept and an experimental demonstration of a 2-D perfect shuttle interconnect with 8 x 8 optical channels are described. We also discuss the scaling behavior and the alignment and wavelength tolerances of the interconnect system.

The addition of optics to electronics in optoelectronic packaging for free-space optical interconnects alters the nature of electrical packaging design methodologies as well as the complexity of implementation. One such complexity arises from the stringent alignment requirement among the microlaser, computer-generated holographic element, and detector. The alignment achieved in the system is a function of assembly tolerance and working environment conditions such as operating temperature. The impact of these constraints on the alignability of the assembly of free-space optical interconnects is quantitatively analyzed.

To design and package optoelectronic (OE) systems more effectively, computer-aided design (CAD) systems are needed in the engineering environment. The use of CAD systems for designing electronic computing systems is well accepted by the electronic community. CAD systems for engineering optical design are also widely used in the optics community. However, design automation of OE engineering requires more than the existing tools for system component design. Also required is research on OE design methodology and a complete set of tools. We explore a new area that will be important to OE system design: OE system CAD. We present an integrated CAD system for free-space optical interconnected optoelectronics that leverages on existing CAD technologies. The details of the system and the guidelines for developing compatible tools are described. Case studies of two OE CAD tools developed using these guidelines are also presented.

Interconnection length and packing density are important parameters in channel-waveguide-based photonic integrated circuits. A multiple-channel crosstalk model is developed and then applied, together with experimental results, to study the minimum bus separation and maximum bus length in a highly parallel single-mode bus array (SMBA) to be used for inter-MCM (multi-chip-module) optoelectronic interconnects. Further investigation of the trade-off between packing density and interconnection length resulting from channel cross coupling provides a rule of thumb for an optimized bus array design. For a given waveguide and cladding index, it is found that waveguide dimensions should be close to the cutoff dimensions of the second-mode to obtain an optimal wave confinement factor. The maximum packing density of an SMBA using coherent light sources is shown to be different from that using incoherent light sources. An example using as criteria an extinction ratio of 20, 1-dB power penalty, and a bit error rate (BER) of 10^-15 is presented. It is shown that the packing density of a polymer-based SMBA ranges from 300 to 750 channels/cm for coherent light sources and from 400 to 950 channels/cm for incoherent light sources with a bus length of 2.0 cm, a core index n₁ = 1.5, and index difference from 0.015 to 0.0015. Further experimental work is conducted to confirm the accuracy of the presented theory.

A novel optical waveguide H-tree design for synchronous global clock distribution on multichip modules, which has nearly zero clock skew, is developed for a distributed computer system environment. The optical waveguide H-tree design utilizes channel waveguides, curved sections, and directional couplers formed using silica glass and silicon oxynitride channel waveguide technologies. Design calculations are presented comparing these technologies that suggest a hybrid combination having the advantages of each. System performance analysis is carried out for both waveguide technologies and the hybrid combination. These calculations demonstrate the feasibility of this approach and show that the achievable clock speed is limited by the laser diode source and photodiode receiver at each chip module, and not by the optical waveguide distribution network.

Optical interconnections can be beneficially employed at the chip-to-chip or backplane level of high-performance computing systems. One method of providing high speed and density interconnections among a large number of integrated circuit chips is with a passive integrated optics circuit. We have developed a method of breaking down arbitrarily complex rectilinear circuits into elementary blocks whose loss and coupling properties are known. Thus, the overall loss and noise for each connection can be calculated. A high-speed algorithm based on this method has been implemented. The high speed of our analysis system makes it suitable for incorporation in an iterative design system, which determines the minimum spacings between the guides and results in acceptable crosstalk and noise levels.

The phase shifting technique for the measurement of a twodimensional birefringence distribution is described and discussed. The birefringent phase difference and azimuthal angle of a transparent material can be determined in the dependence of both measurements on the amplitude and phase of the polarization interferometry. A half-wave plate and a Babinet-Soleil compensator are used as phase shifters for the phase shifting technique. It can measure 256 x 256 values of the birefringent phase difference and azimuthal angle in a short time with sufficient accuracy. This method does not require moving the sample mechanically. The results and procedures for measuring such a birefringence distribution of optical components such as a calibrated Babinet-Soleil compensator, a lens, and a roof prism are discussed.

We investigate the performance of a modified fringe-adjusted joint transform correlator for detecting multiple targets present in an input scene. This technique, involving adjustment of the joint power spectrum (JPS) on the basis of the input-scene-only power spectrum, and apodization of the modified JPS on the basis of the reference signal power spectrum, is found to yield good correlation output. Simulation results are presented to verify the performance of the proposed technique.

A human factors study in which participants viewed 3-D imagery under two task conditions designed to mimic the critical information processing elements of an aircraft control application is reported. In one task, observers judged the relative distance between objects in a 3-D workspace, whereas the other task required observers to extrapolate object positions from course heading cues. Operator performance was assessed for imagery presented with or without retinal disparity cues in three display formats (i.e. , plan view, simple perspective view, and enhanced perspective view) and at three signal-to-clutter levels. The findings indicate that retinal disparity cues reduce the number and magnitude of response errors in the course prediction task, but do not affect observer's response times or ratings of response confidence. The effects of display format varied between the two tasks. In the relative distance assessment task, response times for the simple perspective format were shorter than those for the plan view or enhanced perspective formats. In the course prediction task, response times for the plan view and simple perspective formats were shorter than for the enhanced perspective format. Display format did not affect response errors, error magnitude, or ratings of response confidence.

We propose an improved segmentation algorithm to extract an object from a forward-looking infrared (FLIR) image. The observed FLIR images are considered to be made up of three stochastic models. The first model is in charge of the noise component and is assumed to be independent Gaussian. The labeling of two regions (i.e., the object and the background) in the second model should obey the Gibbs random field (GRF). Finally, we adopt a population parameter to represent the ratio of the size of the object to that of the background. The population parameter eases the tendency to produce similar-sized segmentations. Establishing the stochastic models, we incorporate maximum a posteriori (MAP) estimation to determine the region labels. The optimization of the MAP criterion is achieved by a deterministic relaxation method to converge quickly to a local maximum.

In an interferogram, the variation of intensity background and fringe amplitude displaces the fringe centerlines and gives rise to some systematic phase error if fringe tracking techniques are used. The behavior of this systematic phase error is analyzed in detail. This phase error oscillates from zero in the middle between bright and dark fringes to its extrema in both bright and dark fringe centerlines, but it is not accumulated over the whole image. A 2-D envelope transform with correct envelopes is proposed to remove the systematic phase error. To illustrate, some simulated fringe patterns are processed and analyzed.

We have developed 1.5-μm distributed feedback lasers stabilized on a C₂H₂ absorption line, which are to be used as the frequency reference in a space Fourier transform interferometer intended for meteorological sounding of the atmosphere. The stabilization method is based on the heterodyne spectroscopy technique using a 350-MHz laser diode current modulation. Two 500-cm³ pigtailed stabilized laser modules with 500 μW of useful power at 1540.7 nm were realized. They show a relative frequency stability better than 2.10^-10 for observation times between 0.3 and 300 s.

Cotton is currently graded on its color, leaf, and preparation. Individual component measurements for color and trash are currently reported along with the cotton grades. The cotton industry now requires a method to identify all types of trash in a sample. An image processing system, a test of feature invariance, and two preliminary pattern classification methods used to identify the types of trash in cotton samples are presented. In one approach, the classical grouping performed uses divisive hierarchical clustering based on a normalizecj Euclidian distance metric. Clustering classified 568 trash objects in the training data set with 92% accuracy into bark, stick, and leaf/pepper categories. An area cutoff in the pepper-leaf continuum could handle a separation between leaf and pepper. In the second approach, neural networks minimize identification error in a training data set. Using 75% of a 562 object data set for training, neural networks classified the remaining 134 trash objects into bark versus nonbark categories with a 99.3% accuracy (one piece of bark misidentified). Another network further classifies the nonbark objects into either stick or a combined leaf/pepper category with 96.4% accuracy. Combining both networks gives an accuracy of 96.3%.

A new compact optical processor is proposed for implementing the synaptic interconnections of artificial neural networks. As a consequence of exploiting coordinate transformations, the synaptic elements are compact and applicable to any information. Hence, for use in conjunction with spatial light modulators, the proposed system leads to a programmable neural network. The synaptic interconnections between neurons are performed by means of diffractive optical elements. The required local phase variations of the diffractive optical elements are determined by using the Wigner distribution function. Preliminary experimental verification is presented for the 1-D and the 2-D synapses of neural networks

Five types of Schott glass (GG435, GG455, GG475, BG18, and BG38) have been irradiated up to 1 Mrad using 1.2-MeV γ rays from a Co60 source. The effect of the irradiation on the transmittance of the glasses was studied as a function of the dose for wavelengths up to 800 nm. Three parameters are used to describe the increase of the optical thickness: the saturation coefficient in inverse millimeters, the slope in inverse kilorads times inverse millimeters, and the saturation speed in kilorads; they are given as a function of wavelength. For each glass, a single color center could explain the increase in the optical thickness. This single color center creates three Gaussian-shaped absorption bands that apply to both the saturation coefficient and the slope; the energy, the full width at half maximum, and the amplitude of these bands are given. The data can be used either by an engineer for predicting radiation damage and for choosing the best glass for a given application or by a scientist interested in solid state physics. Guidelines for minimizing the effect of radiation on glass are given and applied to a space experiment to be flown in 1995 on the European Space Agency/National Aeronautics and Space Agency (ESA/NASA) Solar and Heliospheric Observatory (SOHO) spacecraft.

The specific behavior of optical thin films very often leads to limitations of optical system performance. Accurate characterization techniques for evaluating film properties are necessary to understand this behavior. Characterization techniques based on the propagation of guided waves in the thickness of the films appear to be very useful. We report our particular way to determine the refractive index and the thickness of both isotropic and anisotropic thin films. Guided-waves techniques are sensitive enough to detect slight variations of thin film optical constants, so we use them to study the variations of refractive index versus temperature. From this we can obtain the thermorefractive coefficients ∂n/∂T of our layers. Moreover, we can obtain, in some cases, the nonlinear refractive index coefficient. We also measure guided-wave attenuation and laser damage threshold with a digital imaging system.These means, dependent on guided waves, are used in combination for a comparative analysis of TiO₂ and Ta₂O₅ layers made by different eposition techniques (conventional evaporation, ion assisted deposition and ion plating).

Optical design software is developed that includes the capability to model illumination systems. The software enables predicting the intensity distribution of radiation at a plane located at some distance from the source. An illumination system comprising an ellipsoidal reflector and a spherical source is modeled and the results of the analysis are compared to those achieved experimentally.

In scanning electron microscopy, we have discovered that the bottom of deep holes can be observed clearly when a high-energy electron beam is irradiated. To utilize this phenomena, we developed an instrument that generates a scanning electron probe of 50 to 200 keV with a TV scan rate that enables us to inspect a maximum of 8-in.-diam wafers. In the past, deep holes were inspected by observing the crosssectional view of a hole after breaking the wafer into small pieces. Using a high-energy electron beam, we can easily inspect such holes without destroying the samples. We named this inspection method BEASTLI (backscattered electrons assisting LSI inspection). This observation does not depend on specimen conditions, such as the aspect ratio of holes and the specimen charging that often occurs in such cases of insulator observation. This instrument enables us to observe inside the structure of semiconductor devices. Irradiation damage on semiconductor devices caused by unintentional irradiation of unspecified areas, such as threshold voltage and subthreshold coefficient deviation of metal-oxide semiconductor (MOS) transistors, can be recovered by means of hydrogen annealing for 30 mm with a temperature of 450°C.

A system to record laser speckle photographs at framing rates in the range of 10⁵ to 10⁶ frames/s has been developed, based on a repetitively Q-switched ruby laser and rotating mirror high-speed camera. The laser and electro-optic modulator are described. The circuit diagram for an inexpensive high-voltage amplifier, capable of switching 2.5 kV at up to 1 MHz with fall and rise times of 100 and 200 ns, respectively, is given. The resulting optical pulse trains have pulse energy fluctuations at half the driving frequency. We show how these may be suppressed by reducing the time the Q-switch is left open. Both the subharmonic component and its suppression are explained from limiting cases of the laser rate equations. Representative pulse trains over a range of repetition rates are given; pulse energies greater than 20 mJ with pulse energy fluctuations of less than plus or minus one-half of a stop are obtained at rates of up to 500 kHz.

A rotating mirror camera and pulsed ruby laser have been combined to record laser speckle photographs at framing rates in the range of 10⁵ to 10⁶ frames/s. The laser is repetitively Q-switched by means of a Pockels cell, which is controlled by photodetectors inside the camera. This allows well-correlated , double-exposu re speckle photographs to be recorded on two separate runs of the camera. The photographs are analyzed by an automated image processing system to give whole-field displacement data with submicron accuracy. The illustrations show the dynamic displacement field in polymethyl methacrylate due to solid particle impact. The camera/laser system has potential applications for other stress analysis techniques, such as photoelasticity, the method of caustics, and moiré interferometry.

The recursive filtering algorithm, a simple method of filtering electronic speckle pattern interferometric (ESPI) images, is presented and studied. Application software is specially developed for the new method. Experimental demonstration shows that the technique is the most effective and speedy method for the filtering of ESPI fringe patterns so far.

Addition fringe patterns are obtained in real time with electronic speckle pattern interferometry (ESPI) when two pulses are fired within a single field of a COD camera, i.e., within 1/50 s. The ability to use ESPI in this manner means that target deformation can be studied in very severe environments. A major drawback is that the addition fringes are intrinsically noisy and of very low contrast, impeding a full analysis of the deformation. Experimental results are presented for two methods of reducing noise in addition fringe patterns: subtraction of a reference frame and subtraction of addition fringe patterns. The subtraction procedure leads to high-contrast fringes, which can contain information of both target deformation and rigid body motion. An analytical representation of this behavior is presented.

A simplified theoretical analysis based on the step-index planar waveguide model of the mode extinction modulator is presented. The influence of the attenuation of the guided mode is explored experimentally. Two kinds of modulators are fabricated and investigated. The mode-to-mode coupling at region boundaries is found to be dominant for the operation of the device.

A compact soft x-ray reflectometer usable in a small laboratory is developed for measurement of the soft x-ray reflectance of a multilayer mirror in a wide wavelength range, i.e. , including the water window (23 to 44Å). In this reflectometer, the reflectance can be measured as a function of wavelength or incidence angle. A laser-produced plasma soft x-ray source, which is small but has high brightness, makes it possible to construct the compact soft x-ray reflectometer. The soft x rays generated by the source are monochromatized with a grazing incidence reflection grating. Incidence angle dependency of the reflectance can be measured from 2 deg (almost normal incidence) to 85 deg. Reflectances of a Ni/Ti multilayer and a Mo/Si multilayer are measured, and 10.9% at a wavelength of 40.8Å and an angle of 75.1 deg and 38% at a wavelength of 135.5Å and an angle of 25.7 deg from normal incidence are obtained, respectively.

This PDF contains the communication on "Moire technique for linear shear measurement in photographic speckle shearing interferometry."

This PDF contains the communication on "Automated linear shear measurements in digital shearing speckle interferometry."

This PDF file contains the letter “Letter: Comment on the paper: Theory and applications of a surface inspection technique using double-pass retroreflection [see 32(9)2122-2129(Sep1993)]” for OE Vol. 33 Issue 05

This PDF file contains the letter “Letter: Response to Comment on the paper: Theory and applications of a surface inspection technique using double-pass retroreflection [see 33(5)1730(May1994)]” for OE Vol. 33 Issue 05

This PDF file contains the editorial “Book Rvw: High Sensitivity Moire," by Daniel Post, Bongtae Han and Peter Ifju for OE Vol. 33 Issue 05

This PDF file contains the editorial “Book Rvw: Optical Characterization of Semiconductors: Infrared, Raman, and Photoluminescence Spectroscopy," by Signey Perkowitz for OE Vol. 33 Issue 05