This PDF file contains the editorial “Communication Channels: From Editor to Reviewer to Editor” for OE Vol. 34 Issue 05

This PDF file contains the editorial “Optical Science and Engineering in Romania” for OE Vol. 34 Issue 05

A general review of the laser resonator, characterized by its g parameters, is presented. The stable configurations with one and two active media are considered. The laser rod is considered as a thick lens, with refractive power that depends on the pumping level. For the one-rod resonator, fundamental mode operation can be performed in two stability zones. These zones are symmetrical and have the same width as a function of the refractive power of the rod. For a resonator with two rods inside, equal and different refractive powers of the rod at the same pump level are considered. By means of the g parameters and the resonator matrix method, beam characteristics such as the spot size on the mirrors, divergence, beam waists and the positions of the beam waists, and the fundamental mode volume into the rod are described. To obtain fundamental mode operation, plane-plane and convex-concave resonators with one and two Nd:YAG active media are experimentally investigated. The results for energy, beam quality, and divergence are presented.

A new method for improvement of laser pulse characteristics in a Nd:YAG passive Q-switch laser is presented. The method is based on the external controlled small-signal transmissivity of a passive Q-switch crystal. Cr4+:YAG and LiF:F-2 2 crystals are investigated. A high flexibility in choosing laser pulse parameters is obtained.

The intrinsic limitations of emission quantum efficiency of Nd3+ in YAG that lead to heating of active element are analyzed. The main factors characteristic of the system of active ions that lead to heat are the quantum defect and the emission quenching due to energy transfer by cross-relaxation and multisite structure (especially for laser or diode pumping). It is shown that for concentrations of interest for lasers, the reduction of emission quantum efficiency by energy transfer is due to two types of interactions between active ions. The high-resolution data are used to explain the global behavior of metastable level emission kinetics and the concentration reduction of quantum efficiency. An analytic expression for the fractional thermal load is obtained, imposing a lower limit at each concentration. The estimated values of emission quantum efficiency and fractional load are in agreement with reported measured values.

Some of our recent spectral and energy transfer results on Tm3+-based 2-?m solid state laser systems are presented. Based on experimental data, with an improved algorithm and parameterized crystal field calculations, complete energy level diagrams for Tm3+ in YAG and GGG are obtained. The sets of crystal field parameters could be used to estimate a series of important spectral data for laser emission. A discussion of the spectral characteristics and the nature of Tm3+ multisite structure is also presented. The static spectral modifications in Cr3+ codoped with Tm3+ YAG or GGG crystals, due to mutual crystal field perturbations of the two dopants, are connected with Cr3+-Tm3+ pairs. The high-resolution data offer direct evidence that the Cr31-Tm3+ energy transfer is governed for near neighbor Cr3+(a)-Tm3+(c) pairs by a shortrange, most probably superexchange, interaction. The contribution of multipolar interactions should be considered only for more distant pairs, while at large distances, dipole-dipole interaction is dominant. The data suggest that the sensitization with Cr3+ determines not only an efficient way of transfer of excitation from the pumping sources to active ions but could produce changes of the spectal and temporal behavior of the latter.

The possibilities to obtain efficient 3-?m lasing in erbium systems on the self-saturated transition 4/ 11/2?4/13/2 are analyzed. In the frame of the mathematical model based on analytical expressions for population inversion, photon flux density, and quantum efficiency, obtained in the stationary regime, and which explains the main characteristics of 3-?m generation, the influence of various interaction mechanisms such as cross-relaxations, transfer to impurities, excited-state absorption (ESA) and so on is analyzed. It is shown that, although ESA from the terminal laser level could improve the generation characteristics, the driving mechanism for 3-?m erbium lasers is the cooperative upconversion from the terminal laser level.

We propose a method for the calculus of the population inversion between laser energy levels in a helium-neon gaseous mixture by measuring the resonance Faraday rotation. The possibility to study the population inversion versus different characteristic parameters of the electric discharge or of the gaseous mixture is offered. The results are useful for choosing the optimal conditions in realization of population inversion and enable study of the collisions between the atoms, ions, and electrons that are responsible for atomic excitation and de-excitation of different energy levels. In conclusion, the optimal conditions for the occurrence of the population inversion are coincident with those proposed empirically in literature (pHe/pNe=5 and the total pressure about 0.5 Torr).

Data are presented on buried-heterostructure (BH) AlGaAs/ GaAs and InGaAs/AlGaAs quantum-well diode lasers (DLs) fabricated by low-temperature liquid phase mesa melt etching and regrowth. The basic laser structures were grown by either molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD). Native oxides were used as a mask in the processes of melt etching and regrowth. Measurements of excess mirror temperature and parameters of internal second-harmonic generation (SHG) were used for DL characterization. The equalization of beam divergence in both planes, perpendicular and parallel to the active layer, was accomplished by using cylindrical microlenses, at 1 W of radiant power in continuous-wave (cw) operation. The results on medical applications and pumping Er31-doped YAG crystals are reported.

The application of a new admittance-matching method to the design of dichroic mirrors is presented. The method is based on the alteration of both thicknesses involved in the symmetrical period of the matching stack and provides the complete matching at the desired wavelength, i.e., both conditions for the equivalent admittance and phase thickness are fulfilled. A supplementary condition, stated for the derivative of the equivalent admittance with respect to the wavelength, produces a quasi-matching over a wide spectral range. A detailed description of the algorithm used by the computer program that performs this matching is given.

The sensitivity of the parameter determination from measurements of directly measurable quantities is the Jacobian of the inverse mapping. The Jacobian also detects the ambiguities due to nonconformal mappings by changing its sign. The Jacobian formalism applied to phase-shift interferometry shows that this method does not have ambiguities due to nonconformal mappings and reachs its maximum sensitivity for equidistant phase shifts covering the whole range (0,2?).

Expressions for the Seidel aberrations of thin radial gradientindex (GRIN) lenses having a similar structure with the corresponding expressions for thin homogeneous lenses are obtained. By enabling a direct analysis of the relationship between aberrations and lens data, the thin-lens approximation provides new insight into the possibilities and limitations of aberration correction for simple optical systems using radial gradients. It is found for instance that, as in the homogeneous case, within the frame of this approximation the astigmatism of single radial GRIN lenses cannot be corrected if spherical aberration and coma are corrected or if the aperture stop is located at the lens.

The experience in laser optics in the Laser Department of the Institute of Atomic Physics began with the development of the first He-Ne laser in Romania in 1962 (2 years later than the world’s first). Optical polishing and optical coating technology have been developed primarily for the visible and IR ranges, with a continual effort to improve them to increase the quality of optical components and the implicit reliability of the lasers. Ever-increasing attention has had been paid to the investigation, by optical and nonoptical methods, to characterize optical coatings. The correlation of coating characteristics with the deposition technologies could enable the improvement of the technology parameters. Since all the lasers and the applications are equipped with optical components realized in our laboratory, the observations of the users have been important in the activity of improving the quality of optics.

A new mathematical formulation of the focusing method connecting the refractive index distribution of inhomogeneous optical components to the transversally transmitted light distribution is presented. This formulation has the following advantages: the characteristic singularity occurring in the focusing method is avoided; a single numerical integration is used instead of a double one, ensuring a faster data processing; the refractionless approximation is introduced only in the final step of calculations, leading to smaller errors; and the avoidance of a residual logarithmic singularity. An inverse functional transform connecting the intensity distribution in the near field to the refractive index distribution inside the object is deduced and used to obtain analytical test functions. The theoretical results are supported by computer simulations and experiments with gradient-index rods and optical preforms, which have shown improvements in the accuracy, stability, and speed of the method. Moreover, this mathematical formulation for the axisymmetric objects is generalized to a tomographic formulation for nonsymmetric objects using the inverse Radon transform. An efficient algorithm and suitable computer simulations are presented for this case.

We present the experimental results of the characterization of Er31-doped Ti:LiNbO3 waveguides using nondestructive methods. We report results concerning losses and near field and absorption measurements. Waveguide losses are measured in the 1550 nm wavelength region through an interferometric method based on two different techniques: thermal cavity tuning and wavelength sweeping. Homogeneous absorption and emission cross sections are calculated from the transmitted spectrum. The near field measurements are used to obtain the waveguide mode profile through a deconvolution algorithm to correct the probe effect. The resulting field profile enabled us to reconstruct the refractive index distribution.

The electro-optic properties of a new ferroelectric liquid crystal that shows isotropic (I)-chiral smectic-C (SmC*) phase transition are studied. This exhibits bistable electro-optic switching in the SmC* phase. The dependence of the rotational viscosity versus temperature are determined.

Results of the experimental investigation of the nonlinear absorption of microsecond and nanosecond laser pulses in the hydrogenated amorphous silicon (a-Si:H) are reported. Optical transmission due to photoinduced absorption was recorded. After the end of laser excitation, complete relaxation of the light induced darkening was observed. It is suggested that the interband nonlinear light absorption could be explained by taking into account the light interaction with nonequilibrium phonons.

The use of ion probes makes it possible to obtain information on local conditions in pulsed-laser deposition plasmas. Results are presented for KrF laser irradiation of bulk superconducting YBa2Cu3O72x and graphite targets in vacuum. The process is forward-directed, with the highest ion currents and velocities along the target normal. The ion velocity distribution can be well fitted with a Maxwell distribution centered on a flow velocity in the case of the superconductor. Ion energies increase linearly with incident laser energy and are approximately constant with distance along the target normal in the domains considered, but vary considerably for angles away from the target normal.

We report on the construction and study of a high-repetitionrate double-discharge electron beam generator. A synergetic superposition of a pulsed discharge on a continuous one is used to generate an intense electron beam (tens of kilo-electron-volts and hundreds of amperes) that might be used as a useful and inexpensive tool for many applications such as laser generation, x-ray generation, photochemistry, material deposition, and others. To increase the average power the repetition rate is increased in different discharge configurations. Two types of high-voltage switches are used: an electromechanical switch working up to 100 Hz and a thyratron-based switch operating up to 10 kHz. A limit of 714 Hz is found for generator operation at 0.1 l/min flow speed and pulse voltage of about 12 kV in air.

Spectral analysis of CO2-TE-laser-ablated plasma on YBa2Cu3O72-x targets demonstrates a very complex spectrum with emission lines from atomic and ionic species. Plasma temperature is estimated at different moments in its evolution. A good accordance with the values achieved by considering an adiabatic plasma expansion is obtained. Plasma emission intensity is studied as a function of laser pulse energy and, for the same incident energies, a very reproducible amplitude is evidenced. Using a hydrodynamic model, plasma parameters are calculated.

TiNx films are deposited on glass in a modified dc planar three-magnetron geometry. The ellipsometric and reflectance measurements reveal the influence of the substrate bias and of the Ar:N2 partial pressure ratio on the stoichiometry and optical properties of the films. The stoichiometric structure is obtained for only certain bias voltage and Ar:N2 ratio values. The value of the plasma energy wp confirmed the film stoichiometry, as determined from x-ray diffractometry.

The main aspects related to the operating principle, design, and implementation of high-productivity equipment for checking-up the graduation accuracy of optical graduated rules used as a length reference in optical measuring instruments for precision machine tools are presented. The graduation error checking-up is done with a Michelson interferometer as a length transducer. The instrument operation is managed by a computer, which controls the equipment, data acquisition, and processing. The evaluation is performed for rule lengths from 100 to 3000 mm, with a checking-up error < 2 ?m/m. The checking-up time is about 15 min for a 1000-mm rule, with averaging over four measurements.

A portable He-Ne laser at 633 nm, frequency stabilized by saturated absorption in 127/ 2 and built at the Institute for Atomic Physics, Institute for Physics and Technology of Radiation Devices is discussed. The construction of laser head and electronic servo control unit is described. The principle of the arrangement of the electronic circuits in the electronic unit and the tuning procedure of the chosen components are presented. Recent results of an international comparison held at Bureau International des Poids et Mesures (BIPM) was used to characterize the performance of the RO.2 laser against the BIPM4 laser. The mean laser frequency difference calculated on a set of 13 matrix determinations was: ?v=vRO.2-vBIPM4=-1.23 kHz with a repeatability of R(vRO.2)= ±6.8 kHz. The frequency stability expressed as relative Allan variance for sampling time, ?=102 s, was calculated from a 40,000-s time interval as ?(v)/v=1.78×10-12. All measurements were made under the restrictions of the Recommendation 3 (CI-1992) for the lasers suitable for the practical realization of the meter.

In order to monitor the voltage-current (V-I ) and opticalpower– current (P-I ) characteristic curves of pulsed diode lasers, we have designed, built, and tested a compact-size, low-cost electronic device with the function of both supplying periodic variable-amplitude current pulses to the diode laser and transmitting Y-X (either V-I or P-I ) signals to an ordinary oscilloscope. The paper describes the features of the device and the results of its testing by characterizing two sample InGaAs/AlGaAs diode lasers.

Polycrystalline p-type InxGa1-xSb (x=50.20) for optoelectronic devices has been obtained by rapid direct synthesis from highpurity (99.9999%) In, Ga, and Sb. The uniformity of the composition has been checked by neutron activation analysis and also by x-ray diffractometry (Vegard-law approximation). From Hall-effect measurements an acceptor concentration of 3.2x1017 cm-23 and a mobility of 628 cm2/V s for holes, at liquid nitrogen temperature, have been determined, and from absorption measurements, a quite diffuse edge for the optical absorption coefficient resulted. This paper describes the method of rapid direct synthesis of the ternary compound and the techniques used for the characterization of this material for special optoelectronic applications.

Murine lymphoma EL-4 cells were exposed to different pulsed near-ultraviolet laser doses (337.1 nm), generated by light, to investigate some effects of this radiation on tumor cells using biophysical, biochemical, and cytogenetic methods. Our results reveal a good correlation between the growth rate of EL-4 cells and the interrogation irradiation, from 89.7% at 1.5 kJ/m2 to 17.8% at 4.5 kJ/m2. Nucleic acid synthesis was found to be inhibited at any laser irradiation dose. The morphological changes induced by laser irradiation of EL-4 cells and revealed by phase contrast and scanning electron microscopy (SEM) indicate a partial or total (depending on dose) loss of cellular microvillosities, the appearance of different kinds of buds and bleaching all over the cellular membrane, and also numerous necrotic lesions. By reversion of irradiated EL-4 cells, the presence of cells having morphological characteristics of lymphoid dendritic cells was observed by phase contrast and SEM. The cytogenetic analysis showed the presence of different chromosomal abnormalities: chromatidin and chromosomal fractures, rings, chromosomal markers, polyploids, and premature chromatid condensation. Our experimental results suggest the existence of morphological lesions as well as biochemical and genetic lesions induced by pulsed nearultraviolet laser doses in mouse lymphoma EL-4 cells.

In clinical research the efficiency of low-energy laser (LEL) therapy remains controversial. We present here some of the most important results of our clinical experience in this field. We summarize our opinions about the LEL effects in rheumatic diseases, in chronic pelvic inflammatory disorders, in the treatment of some dermatological disorders, and in the recovery of the distal forearm nerve from traumatic lesion after surgical suture. We conclude that these results may be important evidence for the real clinical efficiency of the LEL.

There is current interest in organic materials for use in optoelectronics. The dielectric properties of these materials have proved compatible with low biasing powers, and some methods to improve them have been proposed. We discuss some fatty acids and mixtures of fatty acids, as well as fatty acid–cholesterol, all of them having an important role in biological membranes. They have smectic liquid-crystalline properties in some temperature ranges, this state being involved in the mechanisms determining health and illness. They can be used also in optoelectronic applications, because of the huge optical nonlinearity in the mesomorphic domain. The external self-focusing of a laser beam and nonlinear optical activity have been observed experimentally; by studying the modification of laser pulses in such media, the cholesterol percentage could be estimated. Also the interaction, at different wavelengths, with coherent and noncoherent light was studied.

Laser-induced Fe(CO)5 decomposition at different vapor pressures was performed, and a comparative study of the films obtained thermally (at 10.6 ?m) and photolytically (at 248 nm) is presented. A perpendicular geometry of irradiation and quartz substrates were used. The influence of the incident laser energy on the growth rate and on the chemical content of the films was demonstrated. The film properties are discussed in connection with the irradiation conditions and specific mechanisms involved.

The structure and operation of a holographic interferometer that uses photorefractive Bi12TiO20 crystals as reusable recording materials and computer image processing for rapid and precise interpretation of the fringe patterns are discussed. Different types of two-wave and four-wave mixing were applied to optical testing by double-exposure holographic interferometry. A very convenient matching was found in the phase-conjugation setup for the Bi12TiO20 crystals and usual He-Ne lasers, when the exposures were of ~10 s for light energy densities of 4×10-3W/cm2. Simple algorithms and direct spatial phase reconstruction were used for computer image processing of the fringe patterns.

A method based on holographic interferometry in real time with reference fringes for the determination of liquid parameters in cells with one inclined wall is presented. By studying the interferograms one gets a graphical recording of the spatial distribution of the refraction index of the liquid at a given time.

A new double differential refractometer for student laboratories, based on holographic interferometry in real time with reference hologram and reference fringes, is presented. By studying the interferograms one gets a graphical record of the radial, axial, and temporal distribution of the refraction index in cylindrical tubes. This method permits the determination of the experimental parameters for cases when the relationship between these parameters and the refraction index is known. The paper presents experimental results for gas-discharge parameters.

Under the action of external factors, the dimensions, as well as many internal properties, of bodies change; using holographic interferometry, even very small changes of this kind can be studied. Holographic stress analysis allows one to establish the internal distribution of the stress in the medium, produced by external forces. Transparent samples, in which the stress produces a distribution of the refractive index, are usually used. However, the deformations induced by external forces are able, in some cases, to reveal the internal modifications in nontransparent bodies. Mechanical deformations of some nonhomogeneous solid media (as concrete used in construction), are not accurately elastic. We present a holographic nondestructive method for studying the deformations of bars made of concrete, which are connected with some internal properties of the solid bars, such as the modulus of elasticity. The results we obtained reveal some deviations from the elastic deformation model.

A diffractive optical element has been fabricated which converts a Gaussian CO2-laser beam into a flat-top rectangle. This was accomplished by enhanced photolithographic technology with e-beam generated masks. Experimental patterns of the shaped intensity for a single-mode CO2 laser are presented.

We describe the storage of 2000 images of resolution 512 3512 pixels as a regular matrix pattern of 10310 elements, where each element is angularly multiplexed 20 times in a 25-?m thickness of dichromated gelatin emulsion without crosstalk effect. The surface area of the matrix is 1 cm2. We show good concordance of the angular selectivity between the experimental result and theory. The diffraction efficiency of each of the 20 multiplexed images has been measured and has nearly the same value. Examples of reconstructed images for multiple applications are given, for example, storage of 160,000 images on a 3/2-in. floppy-disk format, that is, about 100 minutes of black-and-white films. Applications to automobile cartography and for storing x-ray and weather forecast images are possible. Colored diffractive images are also possible and are illustrated.

In the literature on computer vision, very few contour detection algorithms are designed to deal with color images. In this paper, we present the multispectral contour detection algorithm (MSCDA) which is designed to process multispectral digital images as well as monochromatic ones. The MSCDA employs a bidimensional matrix of processing modules. The structure of a processing module is biologically plausible in that it consists of a bank of oriented filters. Each filter is a multispectral processing element (MSPE). A MSPE computes a contrast strength value locally from a receptive field characterized by specific orientation, shape, and size. The contrast strength value is a combination of an intensity contrast value with a chromatic contrast value, which are computed separately. Intensity contrast assesses the contrast due to local change in light energy, while chromatic contrast measures the contrast generated by local change in chromatic components. Even- and oddsymmetric MSPE pairs cooperate to extract a combined contrast strength value locally. Each processing module extracts one maximum combined contrast strength response from its bank of MSPEs. The maximum values of the combined contrast strength, provided by the grid of processing modules, form the contrast image. The contour candidate and the contour pixels can be extracted from the contrast image according to a strategy which is developed through simulations on 1-D and 2-D data sets. The MSCDA is compared with existing contour detection algorithms theoretically, and experimental results are shown. The MSCDA accounts for several psychophysical effects which are related to the mammalian visual system and may provide new insights into the understanding of the operational schemes employed by the visual cortex in combining energy, color and texture information for shape detection.

The self-imaging phenomenon is realized by utilizing an incoherent to coherent converter. For this purpose, a photorefractive BSO crystal that becomes uniformly birefringent due to an external applied voltage is employed. Then, an incoherently illuminated one-dimensional grating that locally modulates the induced birefringence is registered. In the readout process, a linearly polarized plane wave from a He-Ne laser is utilized. The ellipticity of the light exiting the crystal will be determined according to the local birefringence. Then, after passing through a polarizer, the coherent output will reproduce the incoherent input. In this way, under free propagation, coherent replicas of the grating will be obtained.

We suggest and verify theoretically a new method of joint digital processing of images distorted by the earth atmosphere. The effectiveness of this method is confirmed by both mathematical simulation and processing of real images of binary stars and unknown spacecraft.

The mechanism of colliding pulse mode locking in solid-state lasers based on the fluctuation model is discussed. A microphysical picture and mathematical expression of the particle number grating are given. The growth processes of mode-locked light pulses are simulated and the output characteristics of mode locking as functions of operating parameters are obtained.

A combined Raman elastic-backscatter lidar for tropospheric profiling of moisture, ozone, and aerosols and stratospheric profiling of ozone, aerosols, and temperature is presented. A XeCl excimer and a frequency-tripled Nd:YAG laser serve as light sources. An eight-channel interference-filter polychromator is used as the receiver. Water vapor, particle extinction and backscatter coefficients, and the particle lidar ratio are determined by the use of the Raman-lidar technique. For depolarization studies the parallel- and cross-polarized components of the 355-nm elastic-backscatter signal are detected. Ozone can be derived from the Raman nitrogen channels as well as from the elastic-backscatter channels by applying the Raman-DIAL and the DIAL technique, respectively. The temperature is obtained from the Raman and Rayleigh signals in the particle-free stratosphere. The apparatus is described in detail. Measurement examples showing the capabilities of the new system are given.

A 2-D SW-banyan network is introduced by properly folding the 1-D SW-banyan network, and its corresponding optical setup is proposed by means of polarizing beamsplitters and 2-D phase spatial light modulators. Then, based on the characteristics and the proposed optical setup, the control for the routing path between any source-destination pair is given, and the method to determine whether a given permutation is permissible or not is discussed. Because the proposed optical setup consists of only optical polarization elements, it is compact in structure, its corresponding energy loss and crosstalk are low, and its corresponding available number of channels is high.

The presence of torsional stress in optical fibers, introduced during splice storage, can adversely affect splice performance and reliability. The relaxation behavior of 900-mm buffer-coated optical fibers following a torsional strain is examined in this study using a transient rheological technique. Samples of different configurations were examined, including completely coated fibers, coated fibers with one end stripped so as to mimic an actual splicing application, and the coating alone with the fibers removed. All samples displayed a power-law stress relaxation with the power-law exponent n dependent on the fiber configuration. The behavior of the coated fiber and that of the coating alone were similar, indicating that the torsional stress relaxation was dictated by the coating itself. Samples with coating stripped from one end showed a lower stress level and a smaller exponent suggestive of a different relaxation mode, which can be interpreted in terms of the stress distribution at the glass coating interface. All samples, regardless of fiber configuration, exhibited very slow stress relaxation, indicating that considerable stress will be present in the fibers in a splice for a long period of time. The effect of the torsional stress on fiber lifetime is discussed using a simplified model.

We report the design and fabrication of multilayer reflective filters for the self-filtering cameras of a Ritchey-Chretien Lyman-a (Ly-a) telescope that uses reflecting multilayer mirrors, polarizers, and filters. The Ly-a telescope is designed to measure the linear polization of hydrogen Ly-a line (121.6 nm) emissions from the solar corona. A key element of the filter design includes the development of p multilayers optimized to provide maximum reflectance at 121.6 nm for the respective cameras without significant angular variation from 0 to 15-deg incident angles. We applied self-filtering concepts to design Ly-a telescope filters that are composed of two reflective mirrors. The calculated value of the net throughput is 28.38% with a 4-nm bandwidth at a center wavelength of 121.6 nm. The measured value is 27.35% with a less than 6-nm bandwidth at incidence angle 10 deg.

A specular surface reflects light only in the direction such that the angle of incidence equals the angle of reflection. Due to this characteristic, conventional approaches to obtain the shape of specular objects have not guaranteed accurate results. Taking into account this characteristic, an optical sensing system is proposed to obtain the threedimensional surface shape of specular objects. Its principle is that a highly focused laser beam strikes the object surface and the specular components of the reflected light are then detected by a beam receiving unit. To achieve this, the system is to be composed of a galvanometer that steers the laser beam’s direction to the desired surface point, a parabolic mirror that reflects the specular component of surface reflection toward its center line and a beam receiving unit positioned along the mirror center line. To evaluate the performance of the proposed optical sensing system, a series of experiments was performed for various measurement conditions. The sensing principle and measurement accuracy are discussed in detail for various objects of simple geometrical shapes.

This study describes a new measurement technique using a single 2-D image of four coplanar points, which are arranged in a square of known size, to measure geometric features on an object, some of which may be hidden from the view of the camera. A new method is also proposed that uses simple equations and an iteration technique to find 3-D coordinates of points on the object relative to a reference point on the object

A new technique has been developed for improving the spectral resolution of spectrographs mounting discrete array detectors. The basic concept is to acquire various spectroscopic images, each one being shifted on the detector by a fraction of the pixel (i.e., the detector resolution element), and to apply suitable numerical procedures in order to extract a spectral profile with subpixel resolution. This technique has been applied to a vacuum spectrograph, adopting the Johnson-Onaka configuration. The dispersion element is a concave toroidal grating that can rotate around a pivot axis displaced from its vertex, in order to maintain a good spectral focus on the detector. The latter is a multianode microchannel-plate array (MAMA) and operates in the photon-counting mode. Several stigmatic images of the H I Ly-? line at 1216 Å emitted by a D2 lamp have been acquired for various rotation of the grating. The results of the application of this new technique and the numerical algorithm are presented and discussed in terms of potentialities and limitations due to the signal-to-noise ratio and intrinsic spectral broadening of the signals.

The capacity of the telecommunication networks is expected to grow to very large throughputs. It is expected that the future Broadband Integrated Services Digital Network (BISDN) large central office will need a switching capacity of the order of Tbits/s when multimedia video communications are widely deployed.

This PDF file contains the errata for “Motion‐compensated interpolation for scan rate up‐conversion”

This PDF file contains the editorial “Introduction to Fourier Optics, Second Edition” for OE Vol. 34 Issue 05

This PDF file contains the book review “Laser Communications in Space” for OE Vol. 34 Issue 05