This PDF file contains the editorial “Editorial: Optical Engineering Readers: We Got Your Input” for OE Vol. 33 Issue 09

This PDF file contains the editorial “Guest Editorial: Optics in South Africa” for OE Vol. 33 Issue 09

The problem addressed here is that of determining the first-order ray-transfer characteristics of an unknown optical system from the positions and directions of rays entering and leaving the system. Mathematically, the problem is a rather daunting one of solving a set of linear equations subject to a set of nonlinear constraints for a total of 10 or 14 unknowns. The nonlinearities are removed by rephrasing the problem, expressed initially in terms of the ray-transfer matrix of the system, into one in terms of the point characteristic matrix. The problem is then solved by converting it to a linear equation in a vector of the unknowns.

We investigate the use of core whispering-gallery modes in a cladded fiber for nondestructive characterization of the fiber core and show how such measurements can be performed by simple extension of known methods for homogeneous scatterers, if the core refractive index is significantly greater than that of the cladding. We describe the effects of dispersion on such measurements. The method is illustrated by using the core-resonance laser emission from a dye-doped solvent flowing in a capillary fiber to demonstrate a linear relationship between mode spacing and core size and to measure the taper of the fiber core.

Diffractive lenses are generally quite sensitive to changes in wavelength. An expression for the spectra of thin diffractive lenses is derived from the Fresnel diffraction integral. Spectra computed with this expression are compared with spectra obtained from computed diffraction patterns. Based on a new definition for the bandwidth of a thin diffractive lens, an expression for this bandwidth is derived.

Optical correlation is sensitive to out-of-plane rotations of the object in the input image. Such an out-of-plane rotation causes the correlation peak to degrade. Here, the degradation of this correlation peak is investigated and a model is proposed to explain its behavior for arbitrary convex objects. First an analytical expression is derived for the peak degradation caused by out-of-plane rotations of flat objects, which is equivalent to a scaling in one dimension. This analytical result compares favorably with experimental results obtained from computer simulation. The 1-D theoretical model is then generalized to explain the behavior of the correlation peak for out-of-plane rotations of arbitrary convex objects. Experimental results for the latter case are also provided.

To obtain economical extraction of ²³⁵U in the molecular laser isotope separation (MLIS) process, 16-μm laser beams must be generated in a parahydrogen Raman cell with high repetition rates and sufficient intensity. Because the intensities of the 16-μm laser beams are dependent on the intensity of the incoming pump laser beams, the intensity of the CO₂ lasers must be kept as high as possible. The maximum intensity has, however, been found to be controlled by the onset of gas breakdown in the Raman cell at too low a level for efficient Raman conversion. Through tests, the origin of gas breakdown in a 2-kHz-repetition-rate Raman cell is identified as particle contamination. The effect of the degree of contamination is determined and compared with experimental results. Conditions are set and modifications implemented on the Raman cell to ensure efficient Raman conversion.

A continuously tunable 3-atm mixed isotope CO₂ oscillator power amplifier (MOPA) chain is developed for a molecular laser isotope separation pilot plant. The characteristics of this laser such as tunability, bandwidth, and output energy are reported. A closed loop gas flow system with a catalyst is employed and its performance is reported.

We report on the construction and optimization of a TEA CO₂ laser with a discharge volume of 15 cm³ and cavity length of 20 cm. Such a short cavity facilitates single longitudinal mode operation. A roots blower is employed to achieve the necessary gas flow rate for highrepetition-frequency operation in a compact design. Output has been obtained at 1 kHz and a stable discharge to a repetition rate of 2 kHz has been demonstrated. The laser is part of a program aimed at the development of an efficient laser system for molecular laser isotope separation. Additional applications in materials processing are envisioned.

Part of a project to investigate the physics and chemistry of alternative fuels in internal combustion engines is reported. Coherent anti-Stokes Raman spectroscopy (CARS) is used to probe the fuel-air mixture in the cylinder of a Ricardo E6 variable compression ratio research engine. The laser system comprises a passively Q-switched single-longitudinal-mode frequency-doubled Nd:YAG laser and a broadband dye laser, both with a pulse length of 15 ns. A crankshaft encoder and electronic delay are used to fire the lasers at specified times during the engine cycle, and CARS spectra are acquired using a 0.75m spectrometer and a 1024 optical multichannel analyzer. Because of the uncertainties associated with collisional narrowing in the theoretical modeling of high-pressure CARS spectra, temperatures are determined by comparing the engine spectra with a library of experimental CARS spectra from a calibrated high-pressure, high-temperature cell. This purely experimental technique is shown to be superior to two theoretical models under the considered conditions, giving temperatures during the compression stroke of the engine with standard deviations of typically 10 K and a possible systematic error of 15 K. Together with pressure records, this information is used as input data for chemical kinetic modeling of the combustion process.

The design concept of a lens that can be used for head motion detection in systems such as virtual reality displays, head-up displays, and simulators is described. A novel concept was chosen to meet conflicting performance requirements. Although the design appears to be quite simple in the optical layout, a number of aspects associated with this design are not readily apparent.

Analytical expressions for reflectance, transmittance, and bilinear transformed reflectance of processed materials containing complex graded refractive index profiles are presented. Oblique incidence is considered. Substantial changes in complex refractive index are modeled by means of a second-order theory, whereas moderate refractive index changes are described by means of a much simpler first-order approximation. An ellipsornetric expression for inhornogeneous layers is also derived using this theory. The performance of the integral formulation is compared to that of the matrix technique by simulations and analysis of experimental data. Simulations using our first-order formulas have a time savings benefit of more than a factor of 10 over reflectance curves calculated by the well-known matrix method. Experimental infrared reflectance of semi-insulating (100) GaAs samples implanted with 280-keV beryllium ions is also analyzed and is compared with our theoretical results obtained from a first-order theory. The Fourier spectrum in the optical thickness domain yielded the position of the peak carrier concentration accurately.

A theoretical examination of the optical properties of layered structures is performed by means of signal flow graphs. Analytical expressions for reflectivity, transmissivity, reflectance, and transmittance are obtained for one-, two-, and three-layer media by using Mason's rule. We also derive alternative formulations of the bilinear transformed reflectance expressed as functions of the Fresnel reflectivity coefficients between the interfaces of the various layers. Under the assumption of lossless materials and normal incidence, these formulas are expressed as functions of refractive indices. These expressions are coincident with those obtained in the past when using the matrix technique. The study of transmittance for layered structures proves, however, that information about thickness and refractive index steps between layers is also available by applying similar digital signal processing techniques to the inverse transmittance.

The properties of thin SiN_x films deposited by computer-controlled electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) from a mixture of SiH₄ and N₂ onto sapphire substrates were investigated by optical transmission spectroscopy in the wavelength range 200 to 2600 nm. The wavelength dependencies of the refractive index n, extinction coefficient k, absorption coefficient α, and the optical bandgap E_g of the films were studied. The optical properties of SiN_x, were found to be strongly dependent on the gas flow ratio during deposition. The optical band gap displays a blue shift with increase of nitrogen content in the layer with values ranging from 1.7 to 4.2 eV.

The electrochemical oxidation of p-type porous silicon prepared under different conditions is investigated. During the oxidation process, bright visible light is emitted from the surface. The time evolution of integrated electroluminescence signals obtained from a silicon photodiode are shown. The signal duration and relative intensity as a function of process parameters during the formation of the porous silicon and during the anodic oxidation are discussed with a view to establish the origin of the luminescence. The experimental results seem to give more evidence for the quantum confinement model. It does, however, not exclude other theories.

A single-axis, three-color light source system with independent triggers, suitable for multiflash schlieren and other photography is developed. The system enables three primary color exposures to be taken on a common film plane, with each exposure, when separated into the primary color components, representing a monochromatic photograph that can be converted to a gray-scale image. The three primary color light sources on a common optical axis are achieved using a specially designed beamsplitter consisting of dichroic filters mounted against a penta-prism shaped holder. Using this penta arrangement and three independent white light flash sources (e.g., xenon lamps), three images can be recorded at independent times on a single image plane. For schlieren applications, this arrangement ensures that all three images have equal sensitivity because they pass through a common schlieren cutoff, and also have the same axis angle (or perspective) relative to the test section. The system has proven to be both low cost and versatile.

Color schlieren has come to mean, not only schlieren images in color, but images where the color can be quantitatively related to the directions of the density gradients in the flow field. A system essentially consisting of three conventional schlieren systems using knife-edge cutoffs, rotated 120 deg with respect to each other, where the light source for each system is in one of the three primary colors is described. It is shown that combinations of these colors (creating a unique color) on the schlieren image resulting from the angled cutoff configuration is a function of the direction of the density gradient only. A variety of relatively inexpensive methods of producing the primary color beams are tested and it is shown that a color beamsplitter using dichroic filters with three standard commercial xenon flash tubes is suitable to obtain good results for high-speed applications. For steady flow applications, a single incandescent lamp used in conjunction with color filters and a diffusing screen is shown to be adequate for qualitative results.

Using the beam propagation method of analysis, the perlormance of a parallel configuration of integrated optical Mach-Zehnder interferometers is examined. These configurations require the interferometers to be spaced closely together to limit the length of the substrate. As a result, the leakage or substrate radiation modes that exist outside each interferometer extend to the point where interference with adjacent substrate radiation modes (and, hence, guided optical power in close proximity) occurs. The radiation mode coupling is shown to have a significant effect on the performance of the interferometer array. The induced change in the mode propagation constants (Δβ) and the corresponding insertion loss due to the radiation mode interference are evaluated numerically as a function of the separation distance between the interferometers. Distortion in the modulation characteristics due to the radiation mode coupling is also quantified and compared with the theoretically expected values.

We introduce the principles of multiple-beam interference in two optical interference structures—the rectangular cavity and the isosceles wedge with a large vertex angle—and prove that they both meet the requirements of interference. We also explain the equivalent and complementary effects of these two structures to Fabry-Pérot interference technology and discuss the distinctive characteristics and the possibility of application. Furthermore, we display our initial experimental results.

Based on mathematical morphology, a novel optical scheme for the real-time preprocessing (removing noise and thinning) of interference fringes has been developed. Three kinds of original interferograms are processed and clear and thin interference fringes have been obtained. The greatest advantage of the scheme is that the preprocessing of fringes can be realized parallelly.

A space-integrating acousto-optic processor conceived for Global Positioning System (GPS) signal acquisition is presented. The main advantage of the proposed system, as compared with traditional ones, is that only one parameter estimation, Doppler shift, is needed, instead of two. The GPS clear and acquisition (C/A) codes are matched to a paratellurite Bragg cell in time-compression hardware with a compression factor of 20. This technique is further exploited for accelerating Doppler estimation. Experimental results show an acquisition time of at most 1 ms.

The major contributors to the dissipation of power by an electromechanical actuator used in a deformable mirror or an active structure are identified. The magnitudes of these power losses for a single actuator are estimated for both single-frequency and random operation of the actuator.

Multiconjugate adaptive optics is an attractive tentative plan for increasing the isoplanatic patch of turbulent atmosphere. Some basic problems relating to this plan have been discussed and corresponding formulas have been given.

Photodynamic therapy (PDT) and on-line fluorescence spectroscopy were carried out on human tumors after 5-aminolevulinic acid (ALA) administration using 633-nm light of a dye laser as therapeutic radiation and as fluorescence excitation radiation. This has the advantages of (1) enabling use of one laser for PDT and fluorescence diagnosis only, (2) enabling the possibility of on-line fluorescence measurements, and (3) exciting protoporphyrin molecules in deep tissue layers. Monte Carlo calculations were carried out to determine excitation and fluorescence photon distribution in case of red and violet excitation radiation. The results show the possibility of depth-resolved measurements on the fluorophore distribution by variation of excitation wavelength. The high penetration depth of 633-nm radiation results in a higher ratio of the 700-nm protoporphyrin fluorescence of the xenotransplanted tumor I_t to the skin I_s compared with 407-nm excitation. No values greater than 1 for the ratio I_t/I_s were found in the case of intravenous ALA injection even for red excitation. Therefore, a large amount of ALA will be metabolized in the skin and can cause photosensitivity of the patient when applied systematically. In contrast, protoporphyrin fluorescence limited to the pretreated skin area was detected in case of topically applied ALA to patients with mycosis funcoides and erythroplasy of Queyrat. The influence of remitted excitation light and of the spontaneous radiation from the laser as well as the possible excitation of food-based degradation products of chlorophyll has to be considered in high-sensitivity fluorescence measurements.

The temperature increase of thermally insulated skin provides useful information about its blood flow and the blood temperature. The measurement of skin temperature by a contact thermometer, such as a thermistor, is not accurate, because it depends on the pressure exerted on the skin by the thermometer. In order to have reproducible measurement of the skin temperature, noncontact temperature measurement is preferable. Suitable insulation is achieved by using a cylinder of lowthermal-conductivity material, covered by polyethylene layers, which is applied on the skin. The polyethylene layers permit partial transmission of the infrared radiation through it. Preliminary results show that both the transient and the steady-state temperature increase can be obtained from measurements of radiation transmitted through the thermal insulation that was applied to the skin, and that the steady-state temperature increase is more closely related to tissue blood flow than the uncovered-skin temperature is.

The main scheme of the measuring cell as well as the sensor device, the analysis conditions, and the results of the quantitative determination of several antigens are presented. Special attention is paid to the immobilization of one of the immunocomponents on the fiber optic surface and three approaches were investigated: (1) covalent binding of the immunocomponent with the help of glutaraldehyde to the surface preliminary treated by aminopropilethoxysilane, (2) direct binding of the immunocomponent to silicon oxide surface by BrCN, and (3) usage of a special membrane closely connected to the fiber optics. The investigations showed that the level of immobilized biomolecules may be achieved almost two fold more by the second approach in comparison with the first one. Good results can also be received by the usage of the special membrane. The sensitivity of the fiber optic immunosensors intended for the determination of the antigens selected was comparable with that made by the enzyme-linked immunosorbent assay (ELISA) method. But in all cases the rate of analyses by immunosensors was much higher than that of the ELISA method, which is the. main advantage of such types of immunosensors.

The uncertainty in selecting the length parameter (the maximum diameter) of a caustic image is investigated. A simple calibration method is used to determine the mode-I stress intensity factor K_I at a crack tip. The accuracy is further improved by using white light. The effect of the pinhole size on the determination of K_I is investigated. The accuracy of the proposed measurement location is demonstrated by comparing experimental results with theory.

The design and characteristics of periodic Butterworth-like passing and blocking filters using a bow-tie-shaped optical fiber ring resonator with two 2 x 2 fiber couplers are presented. Performance parameters, such as the ripple, the contrast, the 3-dB bandwidth, and the maximum output intensity of the Butterworth-like passing and blocking filters, are evaluated. It is found that a completely flat frequency response around the central frequency of the passing band or blocking band can be obtained and that the values of the parameters of the fibers and the couplers for the Butterworth-like passing and blocking filters are only slightly different from those for the first and the second resonances of the transmitted output intensity I₄.

We describe a technique for assembling fiber bundle arrays as needed in optical computing and photonic switching systems. Two 4 x 4 arrays with single-mode and multimode optical fibers were manufactured. Fiber ends were located to within 3 μm of their ideal position and to a pointing precision of 30 arcmin. A third 4 x 8 array was manufactured with single-mode fibers, and fiber ends were located to within 1.5 μm of their ideal position.

Based on the principles of radiometry, the modulation functions of the reflective optical-fiber sensor, which is of the intensity-modulated type, are derived for both specular reflection and diffuse reflection. Theoretical curves are given, based on the expressions for these functions. A comparison is made between the two cases for the different types of reflection, and the problems in applying these models to actual surfaces are discussed.

The frequency of an AlGaAs laser diode (LD) was controlled by using a photothermal effect. If intensity-modulated light from a heating LD is focused on the active domain of another LD, a heat spot changes the effective cavity length of the LD and thus modulates the lasting frequency. For frequency stabilization, frequency shift is detected by a Fabry-Pérot etalon, and it is compensated for by controlling the intensity of the heating LD via a proportional-integral-derivative controller. The highest stability obtained is 2.6x 10^-11 (π = 10 s), which is an improvement of 2 to 3 orders of magnitude over the free-running state. In this method, the concurrent intensity modulation is much smaller than in the current modulation method.

The multilayer laser effect with alternating active and passive layers placed in the Fabry-Pérot resonator is studied. The dependence of the generation threshold on the thicknesses of the layers and the refractive index modulation is described. We show that for the number of active layers N large enough, the minimum threshold amplification follows the rule 1/N³. To decrease the number of active layers necessary for light generation we can either increase the thickness of the active layers or decrease the refractive index of the passive layers. The effect of both is demonstrated.

The method of microwave-induced gas breakdown to diagnose the operating mode structure in a nanosecond-pulse high-power Raman free-electron laser is presented. Modes of low azimuthal and radial index, such as TE₁₁ or TM₀₁, are observed in the Raman free-electron laser experiments. Occasionally, some mixed-mode photographs of the output wave are also obtained, such as the sum of modes TE₁₁ and TE₀₁. In the region of gyroresonance and higher β1, modes with the high index of the electron cyclotron maser are obtained; combined low- and high-index modes are also observed within the same experimental parameters. The results of experimental operating mode observation are discussed and a prediction of mode analysis is made.

A high-repetition-rate oscillator, based on a flashlamp-pumped Q-100-clad athermal phosphate glass rod in a stable cavity, was developed to act as the driver for a high-repetition-rate Nd:glass laser system. Although the athermal properties compensated to a large extent for thermal lensing, birefringence losses in a conventional linear cavity containing a polarizer, as required for Q-switched operation, reduced pulse energy by up to a factor of 3 when the repetition rate was increased from single shot to 50% of fracture-limit pump conditions. Several birefringence compensation techniques were evaluated with the best results obtained in a reentrant (Y-cavity) design, with a Faraday rotator to partially compensate for birefringence and a mirror to reinsert polarizer-rejected light, so that the light quadruple passed the laser head per cavity round-trip and egressed through the output mirror (the only oscillator exit port). Birefringence losses were then reduced to 20%. High-repetition-rate TEM 00 operation was obtained by using a long (223-cm) cavity, and by placing the Faraday rotator/laser head together with a large mode selection aperture next to the curved back mirror.

The relative phase shift of light transmitted through a liquid crystal television (LCTV) panel as a function of the applied voltage on the LCTV can be obtained by writing a Ronchi grating pattern to the LCTV and measuring the intensities in the diffraction pattern at the Fourier plane combined with the amplitude modulation factor. A kinoform is synthesized on the LCTV based on the measured phase shift demonstrating the phase-mostly modulation.

A commonly used estimator for the microtopography of an optical surface is its rms-roughness. Raw surface profile data may contain trending components. Therefore they should be subjected to a detrending procedure before estimating the rms value. This procedure is limited in most cases to the removal of piston, slope, and curvature. Consequently, undesired artifacts may arise, which negatively influence the precision of rms-roughness estimation. In scanning surface metrology, the eigenvalues and eigenvectors of the covariance matrix of the surface can be used for a robust and precise multivariate estimation of rms-roughness.

In an application involving light transmission via total internal reflection, the light is attenuated at each reflection by passage through a thin film. To choose a film that would minimize the attenuation we had to measure the optical properties of Mylar and Teflon. Our results showed that type-D Mylar was preferable.

Optical-quality bulk single crystals of CdAs₂ were grown using the vertical Bridgman technique. Measurement of dispersion of the refractive indices, performed over the 1.2 to 25-μm range of wavelengths, show that they are optically positive and have a great birefringence value, Δn~0.31. Study of optical constant dispersion (ρ) at λ = 1.1 to 2.7 μm demonstrates that CdAs₂ single crystals belong to gyrotropic semiconductors with a right-hand rotation of the polarization plane; the p values reach 180 deg/mm at 1.1 μm.

The linear and nonlinear optical properties of a high-efficiency organic nonlinear optical crystal, 3-methoxy-4-hydroxy-benzaldehyde (MHBA), are investigated. The principal refractive indices at λ = 532 nm are n_x = 1.70331, n_y = 1.5624, and n_z = 1.81376. Calculations show interesting critical phase-matching properties (frequency doubling of the Nd:YAG laser at 1064 nm and diode laser at 830 nm). The nonlinear optical coefficients, d₂₁ = 25d^KDP₃₆ ± 10%, d₂₂ = 10d^KDP36 ± 10%, d₂₃ = 33.3d^KDP36 ± 10%, d₂₄ = 8.3d^KDP36 ± 20%, were determined. MHBA has potential as a practical frequency doubler of Nd:YAG and diode lasers.

An improved synthetic discriminant function for pattern identification is proposed, which is suitable for discriminating one class from all other classes with distortion invariance. By training the samples and their complementary versions from a specified class simultaneously, the distances between the trained class and all other classes are increased in detection space, and therefore high discrimination results. An application to fingerprint identification is given.

Chromatic distortion is one of the main problems of color pattern recognition. I present a scheme for an image system with a TV camera as input device to reduce the effect of chromatic noise. Notation and practical data of Munsell sample chips are recorded through the keyboard and the camera used, respectively. The notation can be looked up rapidly with a neural network. The network performs the transformation from RGB to Munsell space. Another adaptive resonance theory (ART) network is responsible to the transformation from the Munsell space to any desired space. The division of the two transformations ensures high system flexibility.

A low-cost dynamic polariscope is presented. The experimental arrangement is based on the delayed-microflash technique. A LED is used as the flash source. Dynamic photoelastic patterns are recorded after different time delays from the loading point using a CCD camera operating in the time-delay and integration mode. Unlike the conventional photographic techniques, the experiments need not be performed in total darkness. Digital recording provides instantaneous visualization of the patterns and rapid repeatability.

A field measurement program was initiated to determine the utility of the 4.6- to 4.9-μm spectral region as a remote temperature sensing channel. A spectroradiometer (covering the 1.3- to 14-μm region) was used to determine effective surface temperatures of various natural objects both in the 4.6- to 4.9-μm and the commonly used 10.5- to 12.5-μm regions. Comparisons of the effective temperatures obtained from both short-range (30 to 300 m) and long-range (3 to 10 km) measurements are presented. For measurements at short ranges, the deduced effective temperature for each region wascompared with contact temperature measurement of the surface. For measurements over long ranges, the effective temperatures were compared after having accounted for path radiance effects. Accurate path radiance corrections were made from measurements over the tail region of the 4.3-μm CO₂ absorption band.

A method for microscanning in imaging sensors is developed that allows liquid-crystal beam steerers to be used as nonmechanical microscan devices. This submicroscanning method involves using the beam steerers to shift images on a focal-plane array by a fraction of the amount used in typical microscan methods. Interpolation techniques based on interlaced sampling are used to produce images free of aliasing out to twice the Nyquist frequency determined by the focal-plane array. Since a continuous phase ramp is produced by the liquid-crystal beam steerer, dispersion effects due to the gratinglike nature of the devices are avoided. Simulations for both one- and two-dimensional cases are presented, as well as experimental results using a 3- to 5-μm imaging sensor and a liquid-crystal beam steerer designed for operation at 1.064 μm.

We describe an optical-scanning-based imaging system for directly acquiring various spatial derivatives of images, using spatiotemporal modulation techniques in conjunction with electronic heterodyne detection. The technique, which in principle may be adapted to a realtime parallel detection scheme, offers the ability to acquire a variety of first-order and higher-order spatial derivatives. In addition, spatial resolution may be dynamically controlled in a simple electronic fashion. We demonstrate detection of first-order (directional gradients) and second-order spatial derivatives. We also discuss an application that utilizes our gradient detection technique, in a closed feedback system, to achieve contouring and tracking of stationary and moving objects. Experimental results are presented.

We investigate the intrinsic color characteristics used in accomplishing color constancy. The surface reflectance of an object can be divided into two parts: interface reflectance and body reflectance. The body component is the physical basis for determining the surface color characteristics of objects, but it is influenced by geometrical factors in measurement. To eliminate the effect of illumination and geometrical factors we adopt the normalized deviation reflectance, which was suggested by Tominaga, to describe the body reflection characteristics. Then, according to a finite-dimensional linear model, the body reflection characteristics are expressed in terms of weighting coefficients of the constrained basis functions, so as to reduce its dimensionality and make it easy to use in color classification. We choose objects made of inhomogeneous dielectric material as samples and use a grating spectrometer to measure their surface spectral reflectance, from which the description of intrinsic color characteristics can be derived based on normalized deviation reflectance and a finite-dimensional linear model. The experimental results show that this description is very stable under different conditions and also compact, so that it can serve well for color classification.

Spatially modulated Fourier transform spectrometers (FTS) have a throughput advantage over dispersive spectrometers, since an FTS does not require a slit in order to achieve spectral resolution. The traditional implementation of FTSs employs a scanning Michelson interferometer, but since this interferometer is temporally modulated, it is difficult or impossible to use with a target whose spatial and/or spectral signature is changing rapidly. The less common spatially modulated approach to FTS allows all spectral channels to be acquired simultaneously, but cylindrical optics are required to create an imaging version of this type of spectrometer [an imaging fourier transform spectrometer (IFTS)]. This combination of cylindrical and spherical optics, used to achieve both spectral and spatial resolution, increases the difficulty of understanding and controlling the aberrations. An understanding of the effects of these aberrations is essential to developing a spatially modulated IFTS with good spectral and spatial resolution. A spatially modulated IFTS based on a Sagnac interferometer is described, and the effects of aberrations on the spectral resolution, spatial resolution, and modulation are discussed.

Tunable-diode-laser absorption spectroscopy fulfills the major requirements for trace-gas analysis: sensitivity, specifity, high detection speed, and the possibility of simultaneous in situ measurements. The well-known limitations for low-concentration measurements become more and more dominant at sub-part-per-billion levels, where sensitive spectrometers are often influenced by noise, drift effects, and changes in the spectral background structure. While many improvements in instrument development focus on optimizing electronics and optical components, much less effort has been put into postdetection signal processing and adaptive control. Therefore, a transputer-based platform has been developed which allows control of most relevant parameters of a diode-laser spectrometer. Fluctuations in the signal amplitude as well as drift and jitter effects in the frequency domain can cause a significant degradation of system performance and therefore determine the ultimate detection limit. A signal-processing concept with novel aspects for tunable-diode-laser spectroscopy is presented and discussed.

One of the most apparent aspects of motion in real-time airborne systems is acceleration. In this paper, effects of acceleration are considered for two important concerns: image quality and target acquisition. A comparison between the effects of uniform velocity and accelerated motion is presented. There are two opposing considerations when flying over hostile territory: The pilot must fly as fast as possible so as not to be detected or attacked by the enemy, but sufficiently slow so that the degradation of the image quality will not be too severe. Mathematical tools developed recently permit a quantitative analysis of the effects of acceleration on the image quality and acquisition of the target.

This PDF file contains the editorial “Book Rvw: Optical Interconnection: Foundations and Applications," by Christopher Tocci and H. John Caulfield for OE Vol. 33 Issue 09