This PDF file contains the editorial “Editorial: Papers come in many packages!” for OE Vol. 32 Issue 10

This PDF file contains the editorial “Guest Editorial: Microlithography” for OE Vol. 32 Issue 10

Phase shift has been seen by many as a route to increase the resolution capability of optical microlithography beyond the Rayleigh criterion. The initial enthusiasm with which this technology was greeted has been moderated by the realization that prior to its practical application many technical challenges must be overcome. Nevertheless progress has been made. The question to be answered is no longer whether phase shift works, but rather which phase-shift approach and manufacturing technique provide the best practical solutions. We compare three techniques to build alternating phase-shift reticles: (1) deposited spin-on glass (SOG), (2) chemical vapor deposition (CVD) silicon dioxide, and (3) etched quartz. The merits of each approach are judged in terms of lithographic performance, ease of manufacture, and reliability. We condude that the SOG approach offers the best short-term solution to the manufacture of alternating phase-shift masks, although its lithographic performance is somewhat inferior to the other two and its long-term reliability remains to be determined. For deposited oxide to be a viable long-term approach, the oxide must be deposited under the chrome; for etched quartz, the roughness and defect density must be controlled.

Phase-shift mask (PSM) approaches can be classified as either strong or weak. Weak PSM approaches, which are attractive because of their universal applicability to any pattern, are addressed. A simple design algorithm for rim PSM, called biased rim design (BiRD), is described. When used with normal stepper illumination (σ=0.5), the modest benefits of rim PSMs are of questionable value in many cases. However, theoretical considerations show a synergy of weak PSM cornbined with off-axis illumination. One specific combination, termed BiRD/QUEST, is explored through a series of simulations. These results suggest that a properly biased weak PSM with appropriate illumination will allow robust manufacturing of 0.5λ/NA lithographic patterns.

A new wafer rear surface alignment (RSA) technique using a rear surface and canceling tilt effect (RECT) for wafer steppers is proposed. RECT alignment can provide the alignment accuracies of less than 0.03 μm (3σ) that are required for 0.1-μm lithography. The accuracy is almost the same as the resolution limit in the alignment sensor; therefore, position detection errors, which are caused by multi-interference in resist films and the asymmetric profile of marks deformed during manufacturing processes, must be decreased until they can be neglected. The concept of wafer RSA has provided a breakthrough to obtain higher overlay accuracy by fabricating alignment marks on the wafer rear surface. RSA, however, has the disadvantage of a position detection error ε caused by a thickness between the wafer surface and the rear surface, which strongly depends on the wafer tilt. To overcome this problem, RECT consists of two-beam-illumination optics to cancel the error ε. The diffracted beams that are reflected from two separate points on the grating mark include information on both mark positions and light-path difference due to wafer tilt. Thus, the wafer-tilt-induced error can be automatically canceled by processing this information. In an experiment using a six-axis fine positioning stage, it was proven that alignment accuracy can be minimized to as small as 0.015 μm (3σ) for a wafer-tilt angle range of ±50 μrad.

A review is presented on focus effects in optical lithography. Alternative definitions of resolution and depth of focus are given based on an understanding of the interactions of the aerial image with the photoresist process. This interaction points to various aspects of the aerial image that are important from a lithographic point of view, especially the aerial image log-slope. The effects of numerical aperture, wavelength, feature size, and feature type can also be characterized using the log-slope defocus curve, thereby permitting objective comparisons of different lithographic tools. The impact of the photoresist on the response of the process to changes in focus is described as two major effects. First, improving the photoresist results in improved exposure latitude. This in turn allows the image to be further degraded by focus errors and still give acceptable results. Second, submicrometer optical lithography usually results in asymmetrical focus behavior because of the defocusing of the aerial image as it propagates through the photoresist. Finally, several methods for depth-of-focus improvement are discussed and their relative merits and drawbacks are reviewed.

A positive-tone single-layer resist for use with 193-nm radiation has been developed. The system contains a terpolymer of methyl methacrylate, methacrylic acid, and t-butyl methacrylate, along with a photoacid generator. The chemically amplified deprotection of the t-butyl methacrylate into methacrylic acid increases the polarity of the resist and allows selective dissolution in metal-ion-free aqueous-base solutions. The resist sensitivity is less than 10 mJ/cm², and its inherent resolution is better than 0.1 μm. These acrylate-based systems have the potential to be both lower in cost and have better environmental stability than the deep ultraviolet chemically amplified resists that use phenolic resins.

Chemical amplification positive resists using tetrahydropyranyl-protected polyvinylphenol (THP-M) are investigated for deep-UV lithography. Infrared spectroscopy meansurements show that THP-M in the resist film cannot be completely deprotected by photogenerated acid. This causes a poor developability of the resist containing highly tetrahydropyranyl (THP) protected polyvinylphenol in an aqueous base developer. To improve the developability in the pure aqueous base developer, we use partially THP-protected polyvinylphenol. To determine the optimum protection degree, we examine the relation between the dissolution rate of THP-M films and THP-protection degree in developers. A resist formulated from 20% THP-protected polyvinylphenol and bis(tert-butylphenyl)iodonium triflate resolved 0.30-μm line-and-space patterns with the aqueous base development using a KrF excimer laser stepper with a dose of 46 mJ/cm². Postexposure delay effects of this resist system are also studied. The deprotection reaction of THP-M for lower dose during the holding time at room temperature and incomplete deprotection reaction for higher dose are found to deteriorate the exposure characteristics.

Two approaches that control the overflow of silylated material that can occur subsequent to surface imaging of acid-hardened resists are introduced. Treatment of the resist surface with a cross-linking agent [bis(dimethylamino)dimethylsilane] prior to silylation can produce a surface layer with the physical integrity to constrain silylated material. Alternatively, the unexposed areas of the resist may be partially removed by development with a basic solution. The surface depressions thus produced allow volume expansion to occur during silylation without causing overflow.

Liquid- and vapor-phase silylation processes are compared for a 193-nm positive-tone lithographic process using polyvinylphenol as a resist. The liquid-phase process, using a mixture of xylene, hexamethylcyclotrisilazane, and propylene glycol methyl ether acetate, was found to have higher silylation contrast, better sensitivity, and a smaller proximity effect (a decrease in silylation depth for smaller feature sizes). These factors result in a larger exposure latitude, particularly at feature sizes below 0.5 μm. These advantages are greatly offset, however, by the increased chemical costs, which are estimated to be more than 100 times greater than for the vapor-phase process.

Several etching tools are evaluated for the oxygen-based plasma pattern transfer step in surface imaging and multilayer resist processes. These tools include a conventional parallel-plate reactive ion etcher, a magnetically enhanced reactive ion etcher, an electron cyclotron resonance reactor, and an rf helical resonator (Helicon) reactor. The performance of each tool is examined with respect to etch rate, etch profile, selectivity between the imaging layer and the pattern transfer layer, etch uniformity, etching residue, linewidth uniformity, and process latitude.

A study of the dissolution behavior of acid-hardened resists (AHR) was undertaken for spray and spray/puddle development processes. The Site Services DSM-100 end-point detection system is used to measure both spray and puddle dissolution data for a commercially available deep-ultraviolet AHR resist, Shipley SNR-248. The DSM allows in situ measurement of dissolution rate on the wafer chuck and hence allows parameter extraction for modeling spray and puddle processes. The dissolution data for spray and puddle processes was collected across a range of exposure dose and postexposure bake temperature. The development recipe was varied to decouple the contribution of the spray and puddle modes to the overall dissolution characteristics. The mechanisms involved in spray versus puddle dissolution and the impact of spray versus puddle dissolution on process performance metrics has been investigated. We used the effective-dose-modeling approach and the measurement capability of the DSM-100 and developed a lumped parameter model for acid-hardened resists that incorporates the effects of exposure, postexposure bake temperature and time, and development condition. The PARMEX photoresist-modeling program is used to determine parameters for the spray and for the puddle process. The lumped parameter AHR model developed showed good agreement with experimental data.

Total internal reflection holography permits high-resolution, noncontact lithography over very large fields. A production lithographic system has been constructed employing specially developed illumination, focus, and alignment subsystems integrated onto a 6-in. substrate-handling mechanism. The system achieves an imaging resolution of 0.25 μm with a present overlay capability of ± 0.5 μm. A fine alignment system under development has demonstrated a 50-nm measurement accuracy. The technology is well suited to many applications, including the manufacture of flat panel displays, surlace acoustic wave devices, integrated optics, and optical storage disks.

The excimer-laser-based stepper is now expected to play a significant role in the manufacturing of ULSI devices requiring sub-0.4-μm design rule features. They will be used in a mix-and-match strategy along with high NA i-line steppers for critical layers in the production of 64-Mbit dynamic random access memory (DRAM) generation of IC devices. This is supported by the present availability of a number of production worthy high-NA, wide-field excimer stepper models, along with the recent introduction of several process worthy and moderate cost, positive tone deep-UV photoresists. The excimer laser for the stepper, since its introduction in 1987, has evolved from a laboratory instrument to fully production worthy fab-line equipment. The status of such a laser is discussed. We will discuss the operating theory and the design features of an excimer laser; in particular, the discharge chamber, spectral narrowing module, and the wavemeter. Some of the latest technical innovations incorporated into the laser that reduce maintenance intervals and increase reliability are also presented. Finally we will present and discuss the performance specifications of a current production lithography excimer laser.

he effect of 1 93-nm excimer laser radiation on pellicles designed for 248-nm use is studied. The pellicles are transparent at 1 93 nm as well. However, prolonged irradiation causes gradual thinning and eventual rupture of the pellicle. The rate of change depends on the fluence and on the total dose but is not affected by the presence of atmospheric oxygen. Two-photon absorption plays an important role in the interaction between the laser and the pellicle material. Extrapolation to the approximately 0.1 mJ cm2lpulse fluences expected to be used in 1 93-nm steppers indicates that these pellicles will change little for 5everal years in a full-production environment.

The ability of excimer lasers to modify the surface morphology and the electrical conductivity of polymers with spatial resolution on a nanometer scale has been demonstrated. Using holographic techniques with a KrF excimer laser, periodic line structures with periods ranging from 166 to 950 nm have been ablated into polyimide (Kapton) and polybenzimidazole (PBI). The nonlinear nature of laser ablation allows linewidths as small as 30 nm to be obtained, exceeding the resolution expected from linear optics. These experiments establish a new spatial resolution limit for laser ablation and illustrate the dependence of resolution on material properties. This technique has been combined with the ability to modify the electrical conductivity of polymers to produce an array of permanently electrically conducting wires in polyimide with a 0.5-μm width and a 0.9-μm period. The electrical conductivity of these submicrometer wires was greater than 1 Ω^-1 cm^-1.

The effect of 193-nm excimer laser radiation on pellicles designed for 248-nm use is studied. The pellicles are transparent at 193 nm as well. However, prolonged irradiation causes gradual thinning and eventual rupture of the pellicle. The rate of change depends on the fluence and on the total dose but is not affected by the presence of atmospheric oxygen. Two-photon absorption plays an important role in the interaction between the laser and the pellicle material. Extrapolation to the approximately 0.1 mJ cm²/pulse fluences expected to be used in 193-nm steppers indicates that these pellicles will change little for several years in a full-production environment.

Many techniques have been proposed for the reduction or correction of the proximity effect. These include the use of an appropriate beam energy, multilayer resists, dose correction, and correction exposures. Here, special emphasis is placed on dose correction schemes. In particular, the relationship between these and a typical correction exposure scheme (GHOST) is described. The popular "self-consistent" schemes are in widespread use. However, alternative dose correction schemes with attractive attributes exist, although they are not as well known. Two of these are described. One treats electron lithography as a form of incoherent imaging, characterized by a modulation transfer function (MTF). The method consists of transforming the pattern data to account for this MTF, thus eliminating the proximity effect. This scheme is both computationally efficient and accurate. The other scheme is an extension of GHOST in which dose corrections are computed by simulating the effects of a correction exposure: it too is fast and accurate.

A physical method of reducing feature size and proximity effects in sub-quarter-micrometer e-beam lithography is described. A thin layer (50 to 300 nm) of silicon nitride deposited on a semiconductor substrate, prior to resist deposition, has been found to enhance the resist resolution. The samples were patterned with a 50-keV, 15-nm-diam probe generated by a JEOL JBX-5Dll e-beam lithography system. Point spread function measurements in 60-nm-thick SAL-601 on Si are shown to illustrate the resolution enhancement in the nanolithographic regime (sub-100 nm). The technique has been applied to lithography on 400-nm-thick W films, such as would be used in x-ray mask fabrication. The 200 nm of SAL-601 was spun onto W film samples, which were half-coated with 200 nm of silicon nitride. Identical lithographic patterns were written on each half of the sample. On examination of the samples after postexposure processing and development, reduced feature sizes and proximity effects were seen on the sample half with the silicon nitride intermediary layer. For example, in a field effect transistor (FET) type pattern, with a coded 500-nm gap between the source and drain pads, the gate could only be successfully resolved when the intermediary nitride layer was present. Monte Carlo simulations were performed on a CM-200 connection machine. The results show a large number of fast secondary electrons are generated within a 100-nm radius of the incident electron beam. The implications of fast secondary electrons on resolution in e-beam lithography are discussed. The total number of fast secondary electrons entering the resist is reduced by the silicon nitride layer. Simulations compare the thin-layer technique to a bilayer resist technique, used to improve resolution at larger dimensions.

This PDF file contains the editorial “Guest Editorial: Optical Engineering in Hungary” for OE Vol. 32 Issue 10

A double-resonance infrared to far-infrared spectroscopic measuring system with tunable far-infrared lasers and frequency stabilized CO₂ pumping lasers was constructed and used to investigate relaxation mechanisms in far-infrared laser material and also in the presence of added buffer gases.

A small-bore diffusion relaxed N2-laser (P<200 Torr) with longitudinal and transverse excitation in single- and multichannel discharge configurations is developed. We show that the maximum repetition rate and specific average power of the laser are increased with the decrease of the characteristic transverse dimension of the discharge channel. An 8-kHz repetition rate and average power of 6.4 mW are obtained in very compact laser structures. A specific average power of about 160 mW/cm³ is achieved, that is a few times higher than that extracted from largebore plasma tubes. The laser with transverse excitation produces 30-kW pulses at 500 Hz. The waveguide effect in the laser channel and its influence on the spatial distribution and coherence of the laser radiation are also studied.

The relative roles of (1) surface and volume type photoelectric effects, (2) slow and fast laser-induced thermionic electron emission, and (3) optical tunnel emission are discussed from the point of view of the production possibilities of efficient high current density, small divergency electron beams. Angular distribution of photoelectrons emitted from gold target surface by high-intensity pulsed laser radiation at wavelengths of 1060, 343, and 248 nm for the s and p polarization of the grazing incident radiation are investigated experimentally. For the longer wavelengths, where the order of the multiphoton photoelectric emission increases, the ratio of the yields of the surface photoeffect and of the volume photoeffect also increases. The comparative advantages of the surface multiphoton photoeffect of metals as a promising method for the realization of small emittance, high brightness, high current density electron sources are pointed out.

A discrete structure consisting of peaks separated by hv photon energy was found experimentally in the photoelectron energy spectrum, when illuminating a gold target surface by relatively long light pulses (approximately nanoseconds) and using moderate (approximately 120 MW/cm²) intensity of Nd:glass lasers (λ = 1.06 μm). This structure can be considered as the above-threshold photoeffect (ATP) of metal surfaces. Its occurrence at surprisingly low laser intensities [which are four orders of magnitude less than the typical intensity range of the analogous above-threshold ionization (ATI) of atoms] was observed when the space charge was considerably eliminated.

ArF excimer laser ablation of corneal tissues (in vitro, pig) is investigated. Scanning electron microscopic analysis shows that the spatial resolution of the ablation is better than 1 μm. The etching rate and etched depth is found to be proportional to the logarithm of the laser fluence and the number of shots, respectively. To investigate the dynamic processes a laser-based, ultrafast photographic arrangement was constructed having a temporal resolution of 1 ns. The maximum speed of the shock wave generated during ablation is found to be as high as 4000 m/s. The ejection of the ablation plume with plume-front velocities in the range of 600 m/s is also observed. A new type of surface wave generated by the recoil forces of the ablated material is found. The amplitude of this surface wave can be as high as 0.4 mm.

Laser analytical methods are used for the determination of surface sodium impurity distribution on silicon samples. In the first experiments, the spots on the surface of the sample were atomized by ruby laser pulses and the sodium atoms were selectively ionized by resonant ionization, thus the simple ion detection yielded the sodium surface contamination density. The second method applies excimer laser ablation, and the generated ions are analyzed and detected by a reflectron-type time-of-flight mass spectrometer. The analytical arrangements are applied for tokamak plasma investigations. Silicon plates as deposition probes located in the edge plasma region are exposed to several tokamak discharges, which are contaminated by pulsed sodium impurity injections. Surface analysis of the samples enables determining the sodium impurity fluxes in the tokamak edge plasma region, which are characteristic of particle transport properties. The high sensitivity of the method applying resonance ionization enables the analysis of single discharges, whereas the application of mass spectrometry offers the possibility of detecting several impurity materials.

Wave optical studies have been made for ultrashort pulse propagation through a lens, a grating, and a slit. The intensity distribution of an ultrashort pulse was calculated in the vicinity of the focal point of a lens. Analytical expression was found for the temporal and radial intensity distributions in the focal plane. For the case of a grating, the pulse front becomes curved far away from the grating and there is a time difference between the edges of the pulse. An analytical form was obtained for both the pulsewidth and the shape of the pulse front. For the case of a slit, calculations were made for a short pulse with tilted pulse front based on the Fraunhofer diffraction theory. A small, additional pulse appears behind the slit, which is off by the angle of the pulse front tilt from the direction of the original propagation. This pulse was predicted by the boundary wave theory. For white light illumination behind the slit, no interference can be seen at the maximum of the intensity; the interference pattern diverges from the maximum of the intensity.

Femtosecond pulse fronts suffer a time delay across the beam when propagating through diffraction gratings or dispersive prisms. A general relation was found describing the tilt angle γ of the pulse front as, tanγ=λdε/dλ where dε/dλ is the angular dispersion of the grating or prism and λ is the central wavelength of the pulse. The expression is valid for any spectral device having angular dispersion (e.g., Fabry-Pérot interferometer, Lummer-Gehrcke plate, and Michelson echelon). The tilt angle is shown to have a close relation to the classical uncertainty principle.

Based on the analysis of known, corrected, classical triplet type objectives and given the basic specification requirements, diagrams of the constructional length and image distance of their equivalent thin lens systems are prepared. By keeping the constructional length and image distance constant and applying simple formulas, the focal lengths and air gaps of the thin lens triplet variations can be generated. These variations can be used for selection based on any criteria, such as, for example, the Petzval sum. According to the original description of the Petzval sum, to our computational experiences and to the examples given, which were the results of precise corrections, we concluded that also in case of triplets, the designer should target the minimal Petzval sum, which is constrained only by the basic specification data.

We discuss the evaluation and design of wide-field-angle acircular lens systems in anisotropic planar waveguides. After a short summary of the applied ray and wave optical relations, we examine the aberrations of systems that were optimized for an isotropic waveguide but are embedded in an anisotropic one. We show that effects of anisotropy must be taken into account in the design of wide-field-lens systems. We present a four-element acircular lens that was optimized using a merit function computed for uniaxially anisotropic media.

Data of a glass filter combination converting the spectral responsivity of the GaP photoelement to the window-function cutting off the UV-A band and a probe structure realizing the cosine character directional response are given. Systems for measuring the spectral characteristics of the photoelement and the filters, and for measuring the directional characteristic of the probe, as well as the software that optimizes the thicknesses of the filters for reaching the minimal integral error are touched on.

A semiconductor rib waveguide was designed using AUTOCAD for layout and the finite difference beam propagation method to calculate field distribution. The near-field method accomplished by an IR image processing system was used to investigate the field distribution in the 1.3-μm region.

Optical coating suppliers specialized to meet special needs of laser developers often have to face new challenges to help them in building high-performance, high-efficiency lasers. Some aspects of laser optical coating design and manufacturing are discussed. First an unconventional coating deposition technology, termed the reactive electron beam evaporation under reduced oxygen pressure, is reviewed. The technology is applied for the TiO₂/SiO₂ and the Ta₂O₅/SiO₂ material pairs producing optical coatings with low absorption and scattering losses. Then some concrete application problems and their solutions are presented using our technology: high reflectance UV mirrors containing UV-grade HfO₂ layers; high-damage-threshold, visible/near-infrared power optics; mirrors with extended high reflectance bands (all-dielectric broadband reflectors); and elements of a specially designed mirror set for femtosecond pulse Ti:sapphire lasers. The mirror set for the Ti:sapphire laser has been optimized for both phase and amplitude characteristics.

A new method for the evaluation of the effects of the finite spatial resolution of the recording material on the reconstructed holographic image is presented. The method is based on substitution of the amplitude modulation transfer function (the square root of the modulation transfer function) of the recording material into the double Fresnel-Kirchhoff integral describing the complex amplitude of the reconstructed image. Numerical calculations have been carried out for holograms recorded in silver halide and thermoplastic-photoconductor materials. The contrast of the reconstructed image as a function of various recording parameters, such as the resolution limit and slope (in case of silver halides), and the center and width (in case of thermoplastics) of the amplitude modulation transfer function of the recording material, the object position and the reference beam angle has been computed. Thin holograms of microline objects have been studied in several recording geometries, including one with a tilted object plane.

Difference holographic interferometry (DHI) can be used for direct optical comparison of two nominally identical objects (master and test) and gives the results of the comparison in the form of an interference pattern displaying the difference in deformation, shape, or refractive index distribution change of the two objects. The concept of the DHI is discussed and the main techniques and typical applications are presented. Finally, theory is briefly overviewed.

A light-scattering airborne particle counter with a new optical design having the optical sampling chamber outside the laser resonator is presented. This device can be used to measure the size distribution of particles from a diameter of 0.3 μm in a wide concentration range with high reliability and stability. Some results of the applications of the device in highly contaminated environments are reviewed.

Although modern theoretical physics states that the velocity of light does not add to the velocity of the light source, and so according to Einstein's theory the velocity of light is independent of the coordinate system, from time to time scientists try to disprove this axiom. We tried to build the most accurate experimental setup according to our technology.

Ideally an acousto-optic tunable filter is capable for selecting a single optical wavelength from a broadband polychromatic light beam simply by its electronic tuning. In practice, however, both the wavelength resolution and the operating wavelength range of the filter are limited by its electric and optical properties. An experimental configuration of a computer-controlled, fast acousto-optic spectrometer, based on an acousto-optic tunable filter operating in the 400- to 800-nm visible range with an average resolution of 10 nm is constructed and studied. The spectrometer has been operated in broadband optical measurements, such as determination of transmission spectra of complex, multilayer optical thin films and also real-time, in situ monitoring of evaporation processes. During the experiments, an anomalous behavior of the filter was observed that seriously limited the performance of the filter in the blue region. Some requirements necessary for spectrometer application are summarized and theoretical and experimental results are given illustrating the existence and also the elimination of this anomalous behavior.

The development of a data acquisition system for a high resolution motion analyzer is discussed. The displacement measurement is based on a Michelson-type heterodyne interlerometer. The gained detector signals of the interferometer are processed by the direct phase comparison method. This method makes it possible to achieve a resolution equivalent of 1/512 of the applied optical wavelength, without the intricate signal conditioning needed by the commonly used phase-locked loop frequency multiplication or analog signal multiplication methods. The main technical data of the system are 1.25-nm resolution, 20-m measuring distance, and 60-kHz sample rate. The accuracy is better than ± 10 nm ± 0.1 ppm within a velocity range of ± 1.8 m/s and an acceleration range of ± 9900 m/s².

Special glass-filters are designed for imaging colorimetric purposes using full-filter technology. Spectral characterization of a CCD camera is performed and a CIELUV chroma difference map is used to characterize a globally filtered detector.

In subcarrier multiplexed optical transmission systems the modulation linearity of the transmitter plays an important role because that nonlinearity gives rise to serious harmonic and intermodulation distortions. Therefore the modulation linearity of the laser has been significantly improved by applying an active matching technique. For that purpose, the microwave impedance of the laser has been measured as a function of the bias current and frequency. Based on the measured data, a nonlinear equivalent circuit has been derived that was used in the matching process. As a result, a significant improvement in the laser modulation linearity has been attained.

Light-in-Flight recording by holography makes it possible to perlorm accurate three-dimensional shape measurements by single-line contouring. Because ultrashort light pulses are used, both stationary and moving objects may be recorded, e.g., fast-rotating turbine blades, mobile scale models, active human beings, etc. The evaluation is accomplished by an image processing system that reads the contouring line that varies along the hologram and transforms it into spatial coordinates, thereby measuring the three-dimensional shape. There are a number of possible application areas of the method, ranging from practical engineering to medicine.

The reconstruction method of phase information "frozen" in an electron hologram is discussed. The experimental results show that the double-exposure method (which does not need laser reconstruction) cannot only obtain directly the phase information, but also gives qualitative and quantitative results. This means also that one can obtain simultaneous information about both the amplitude and phase in an experiment in an electron microscope

Prediction of the performance of IR sensor systems in the detection and classification of features in an image requires estimation of the sensor signals produced by a given feature (source) and the background in the image. This process includes estimation of the effects that the detector, the scanning system (if used), and the optical system have on the performance of the system in a specified environment. The analysis of sensor performance takes into account the emission characteristics of the source and background and often assumes an extended source. For some tasks, the apparent size of a source, as well as the emission characteristics, must be taken into account in determining the scene contrast produced by the source. This requirement to account for the apparent size of a source arises as a result of the reduction in image contrast of a source of small apparent size due to optical blurring caused by the formation of the image. An analysis of the effect of apparent source size, the detector instantaneous field of view, and optical blurring on the image contrast produced by imaging IR sensor systems is presented.

A hybrid optical/digital configuration to implement a highspeed correlator is described. The input data is digitally Fourier transformed at video rates utilizing specialized digital signal processing chip sets and the computed spectral phase data passed to an electrically addressed phase modulating spatial light modulator (SLM). Successive templates, which are stored as angle multiplexed volume holograms in a photorefractive crystal, are reconstructed and optically correlated with the current input scene during an interval in which the SLM display is held stable. In this way, shift invariance, one of the major advantages of the correlation technique, is preserved. Of critical importance to the speed of operation are the energy losses of the coherent wavefront through the system and the rate at which correlation plane data can be converted to an electronic signal; both of these issues are considered to estimate that at least a 3-kHz search rate is achievable from a 1000 template memory with system components currently available.

Human fingerprints comprise a series of whorls or ridges. In some special cases, these whorls are broken by so-called secondary creases-colinear breaks across a sequence of adjacent ridges. It is a working hypothesis that the presence of these secondary creases form a physical marker for certain human disorders. A technique to automatically detect such creases in fingerprints is described. This technique utilizes a combination of spatial filtering and region growing to identify the morphology of the locally fragmented fingerprint image. Regions are then thinned to form a skeletal model of the ridge structure. Creases are characterized by colinear terminations on ridges and are isolated by analyzing the Hough transform space derived from the ridge end points. Empirical results using both synthetic and real data are presented and discussed.

This PDF file contains the editorial “Book Rvw: Fabrication Methods for Precision Optics," by Hank H. Karow for OE Vol. 32 Issue 10

This PDF file contains the editorial “Book Rvw: Polymers for Lightwave and Integrated Optics," edited by Lawrence A. Hornak for OE Vol. 32 Issue 10