Abstract: A model for Raman scattering by a molecule adsorbed at the surface of a spherical particle is articulated by treating the molecule as a classical electric dipole. This follows Moskovits’s suggestion [ J. Chem. Phys.69, 4159 ( 1978)] and the experiments by Creighton [ J. Chem. Soc. Faraday Trans. II, 75, 790 ( 1979)] that such a system may exhibit SERS similar to that at roughened electrode surfaces. The molecule is stimulated by a primary field comprised of the incident and near-scattered fields. Emission consists of the dipole field plus a scattered field, each at the shifted frequency. Addition of feedback terms between the dipole and the particle makes only a negligible contribution to the fields. For pyridine adsorbed at the surface of a silver sphere, the 1010-cm−1 band is enhanced by ~106 if the radius is much less than the wavelengths and the excitation wavelength is ~382 nm, a wavelength for which the relative refractive index of silver is close to m=2i. Detailed results are given for the effect, upon the angular distribution and the polarization of the Raman emission, of particle size, distance from the surface, excitation wavelength, and location of the molecule upon the surface. These results simulate those observed at roughened silver electrodes and suggest that the mechanism of SERS at those electrodes may resemble the electromagnetic mechanism elucidated here. We predict that comparable effects should be observed for fluorescent scattering.

Abstract: Several low-order Zernike modes are photographed for visualization. These polynomials are extended to include both circular and annular pupils through a Gram-Schmidt orthogonalization procedure. Contrary to the traditional understanding, the classical least-squares method of determining the Zernike coefficients from a sampled wave front with measurement noise has been found numerically stable. Furthermore, numerical analysis indicates that the so-called Gram-Schmidt method and the least-squares method give practically identical results. An alternate method using the orthogonal property of the polynomials to determine their coefficients is also discussed.

Abstract: Propagating beam solutions for optical waveguides can be made to generate such mode-related properties as propagation constants, relative mode powers, and group delays with high precision and considerable flexibility. These quantities are needed in the analysis of optical fiber dispersion. The technique requires the generation of correlation functions from the numerical solutions of a wave equation. These correlation functions are in turn Fourier-transformed with respect to axial distance z. The resulting spectra display sharp resonances corresponding to mode groups, and the positions and heights of these resonances determine the previously mentioned mode properties. The spectral analysis is made highly accurate by the use of line-shape fitting techniques. With this method, mode group delays can be determined to a precision of +/-0.12 psec/km using a computation covering a 5-cm propagation path.

Abstract: A fiber-optic coil for use as the sensor loop of a fiber optic gyroscope includes a first optical fiber segment wound as radially successive coiled layers around a coil bobbin in a first region thereof, and a second optical fiber segment wound as radially successive coiled layers around the coil bobbin in an axially adjacent second region thereof. The first and second optical fiber seg ments are joined to each other through a longitudinal middle portion, which is positioned in the radially in nermost coiled layers of the first and second optical fiber segments adjacent to a longitudinal center of said coil bobbin. Each of the first and second optical fiber segments is wound in alternate axial directions in the radially successive coiled layers. The first and second optical fiber segments may be integrally joined to each other by the longitudinal middle portion, or may be separate from, but joined to, each other by a depolarizer across the longitudinal middle portion.

Abstract: There is no inorganic material that would satisfy the low index requirement of a single-layer antireflective coating for commercial soda-lime glasses. Such an antireflective coating would increase transmission 4-8% and cause corresponding efficiency increase in devices where energy is transmitted by radiation, e.g., solar collectors, and cathode ray tubes. MgF(2) with an index of 1.38 (vs 1.23 needed) is the lowest index coating material available and widely used by the industry. In this work, possible applications of porous oxide films as an antireflective coating were investigated. A porous aluminum oxide film is deposited on glass surfaces from a clear organometallic derived sol. The index of the oxide coating is reduced by the presence of pores hose size is <100 A; this constitutes up to 64% porosity. These pores, being considerably smaller than the wavelength of light, do not interfere with the optical transparency of the material but reduce the index of refraction; thus they make it possible to obtain transparent oxide materials and coatings with very low index.

Abstract: A theory is presented of the propagation of Gaussian pulses in single-mode optical fibers by expanding the propagation constant in a Taylor series that includes the third derivative with respect to frequency. The light source is assumed to have a Gaussian spectral distribution whose width relative to the width of the Gaussian signal pulse is arbitrary. Formulas are derived for the spectrum of the ensemble average of the optical pulse, from which the shape of the average pulse itself is obtained by the fast Fourier transform. Also derived is an expression for the rms pulse width. The theory is applicable at all wavelengths including the vicinity of the zero first-order dispersion point.

Abstract: The subject of gradient-index optics dates from the 1850s. However, only in the last 10 years has it been possible to design lenses, manufacture materials, measure the properties, and fabricate finished lens elements. The current status of gradient-index optics is reviewed.

Abstract: A method is described for obtaining real-time in situ size and velocity measurements of spherical particles or droplets using crossed-beam interferometry. The optical arrangement, which is similar to a dual-scatter laser Doppler velocimeter (LDV), consists of two laser beams focused to a crossover region. Droplets passing through the focal volume scatter light to the collecting lens situated at some off-axis angle. The dual-beam light scatter is analyzed by the geometric optics theory to relate the scattered fringe pattern to the droplet diameter. Because the droplet size measurement is based on the relative phase shift between the two light waves passing through it, the method is independent of the incident intensity, droplet absorption, or absolute scattering intensity. Experimental measurements of monodisperse droplet streams show good agreement with the theory. The technique can be applied to spray-droplet measurements over the size range of 3 μm to 5 mm. By using large off-axis scatter detection angles, the measurement of the droplet size and velocity distributions in relatively dense spray environments is made possible.

Abstract: Aberration-corrected concave gratings with curved and variable spacing grooves are ruled with a numerically controlled ruling engine. In the design of aberration-corrected concave gratings, mechanical methods allow more freedom to choose the amount of space variation than do holographic methods. A highly efficient visible–UV monochromator and a coma-type aberration-reduced Seya-Namioka monochromator have been designed and fabricated using mechanically ruled aberration-corrected concave gratings. The gratings can be used with VUV monochromators and spectrographs with improved image focusing properties.

Abstract: Possible sources of errors in depolarization data are analyzed with special reference to the rotational Raman contribution to the optical depth. It is shown that the depolarization data now available are so accurate that their uncertainty affects the calculated Rayleigh optical depth by less than 1%, and consequently, the anomalously low extinctions occasionally reported must be due to systematic errors of measurement rather than errors in the Rayleigh optical depths.

Abstract: Bend-induced retardation and twist-induced rotation in single-mode optical fibers are important variables in the design of optical fiber current measurement systems. Bend-induced retardation varies with the square of the curvature and is believed caused by a waveguide geometry effect. Twist-induced rotation varies with the angle through which the fiber is twisted and is produced by torsional strain in the fiber. Both effects were found highly reproducible and to have small temperature dependence. Neither effect should significantly limit the performance of optical measurement systems using single-mode fibers.

Abstract: A three dimensional eye tracker, for measuring as a function of time the point in three dimensional space on which the eye is fixed, includes a portion which functions as a two dimensional double Purkinje eye tracker for measuring movement of the eye in rotation and translation, an automatic optometer portion for measuring the refractive power of the eye, and a common optical path simultaneously to provide corrections for both portions of the instrument. The two dimensional eye tracker portion incorporates a means for directing a beam into the eye, thereby forming first and fourth Purkinje images, and measuring means responsive to the first and fourth Purkinje images to generate output signals indicative of eye rotation and translation. The automatic optometer portion alternately directs a light beam through different areas of the eye lens and includes a mechanism for altering the directed light beam until the image on the retina does not move. The common optical path for the light beams includes elements that stabilize the eye image in a way to make alignment of the subject in the instrument relatively easy and also to avoid errors both in measurement of refractive power and for direction of gaze due to translation and axial movement of the eye. Polarizers and mechanical stops are incorporated in the optometer portion to provide optical isolation between the eye tracker and the optometer portions, and electrical filtration is provided in both portions of the instrument further to avoid interference.

Abstract: Multiphoton ionization (MPI) spectroscopy is rapidly evolving into a valuable adjunct to VUV spectroscopy for the study of the highly excited states of molecules. The technique is described, and several examples are given of its applications. Studies of the 3pz Rydberg states of the methylbenzenes and of the 1B2u state of benzene show that state assignments can be made and new multiphoton structure seen that is not available in one-photon spectra. MPI of benzene in a supersonic jet demonstrates dramatic resolution improvement and shows that natural linewidth information can be gained for large molecules. Collisional effects in MPI spectra are briefly discussed with reference to Xe and to laser enhanced collisional broadening of nitric oxide in the supersonic beam.

Abstract: A set of differential equations is derived which specifies the shape of two aspherical surfaces of a lens system that will convert an incident plane wave with an arbitrary energy profile into collimated radiation with a uniform energy distribution. As an example, a lens system is designed that converts a laser beam with a Gaussian energy profile into an expanded beam with a uniform energy distribution. Off-axis rays are then traced through the lenses in order to analyze the performance of the lens system.

Abstract: Measurements of angular scattering due to surface roughness were taken from a 24-layer dielectric mirror and compared to theory. In addition, the top surface roughness of the multilayer stack is analyzed from Talystep profilometer measurements. These roughness data are used to obtain a roughness spectral density function to be used in a vector multilayer scattering theory. The theory uses three multilayer stack models to incorporate possible effects of different degrees of correlation between interfaces of the stack. It was found that the angular scattering calculated using the experimentally obtained roughness spectral density function agreed remarkably well with the measured angular scattering data. This is especially true if care is taken to differentiate between particulate and roughness scattering. For the sake of comparison, the angular scattering from an aluminum film is also given, and differences from scattering from the multilayer mirror are noted.

Abstract: The application of a multiple-pass Herriott cell to stimulated Raman scattering (SRS) is evaluated and demonstrated. The cell combines a long optical path length with periodic refocusing to enhance Raman gain. This technique is especially useful for reducing SRS threshold pump power in the IR where the Raman gain is low. This paper presents an analysis and design procedure for a multiple-pass Raman gain cell and gives experimental results for SRS in H(2) gas.

Abstract: A laser absorption spectrometer is described which uses a tunable diode laser and a 1-m multipass White cell to detect NO(2) in air with a sensitivity of better than 100 ppt. The modulation techniques employed to achieve this sensitivity are described in detail, and the noise mechanisms, which currently limit the detectable absorption coefficients to greater, similar 10(-7) m(-1), are examined.

Abstract: The possibility of interpolating the internal quantum efficiency of silicon photodiodes using a model with three adjustable parameters is investigated. The three parameters are determined from self-calibration measurements at 351, 476, and 800 nm. The internal quantum efficiency is then interpolated to 407 and 677 nm using the model. The calculated results are compared with direct measurements referenced to an electrical substitution radiometer. A difference of 0.6% was observed at 407 nm. This is probably significant, arising from inadequacies in the internal quantum efficiency model and possibly from volume recombination that is not accounted for by the self-calibration procedure. An insignificant (<0.1%) difference was observed at 677 nm.

Abstract: Frequency-selective optical couplers in which a periodic perturbation in refractive index induces contradirectional power transfer in parallel single-mode waveguides are analyzed. Expressions for the spectral response are obtained by solving the coupled-mode equations. It is shown that by varying the amplitude of the periodic perturbation along he direction of propagation, the sidelobes present for the case of a uniform perturbation can be substantially reduced. Calculations are made of the mode propagation constants and coupling parameters for two rectangular-core waveguides with a periodic surface corrugation in the region between them. By using these results, design parameters and theoretical performance characteristics for a coupler with high transfer efficiency, low cross talk, and low reflection efficiency in the primary waveguide are determined.

Abstract: A MTF is derived that includes isoplanatic effects of tilt correction or short-term imaging systems. The MTF is used to predict degradation in Strehl ratio or resolution due to tilt decorrelation on offset paths for long horizontal paths through constant turbulence and for space-to-earth paths through a path-dependent structure constant C(2)(n).

Abstract: The use of laser-induced water Raman backscatter for remote thin oil film detection and thickness measurement is reported here for the first time. A 337.1-nm nitrogen laser was used to excite the 3400-cm-1 OH stretch band of natural ocean water beneath the oil slick from an altitude of 150 m. The signal strength of the 381-nm water Raman backscatter was always observed to depress when the oil was encountered and then return to its original undepressed value after complete aircraft traversal of the floating slick. After removal of background and oil fluorescence contributions, the ratio of the depressed-to-undepressed airborne water Raman signal intensities, together with laboratory measured oil extinction coefficients, is used to calculate the oil film thickness.

Abstract: The performance characteristics of a 1024-element self-scanned photodiode array, related to its use as a multichannel spectrometric detector are described. The parameters discussed include, spectral and temporal response, blooming, geometric accuracy, noise sources, dynamic range, signal integration and spectral as well as spatial resolution.

Abstract: The induced optical phase change produced when a static pressure is applied to the test arm of an interferometric single-mode fiber optic hydrophone is examined in terms of hydrostatic and radial mechanical models. The expressions for the models are given in terms of a 3-D solution to the equations of elastostatics for multilayered cylinders. The induced phase change is calculated using both models for various values of the diameter and elastic properties of fiber jacket materials. It is shown that the phase change predicted from the 3-D approach for each model can be adequately described in terms of much simpler 2-D plane strain models. Calculations show that the hydrophone sensitivity of a jacketed fiber is amplified compared with a bare fiber. The largest increase in sensitivity is predicted with the radial model. Calculated sensitivities for the hydrostatic model are shown to correspond closely in value with static pressure sensitivity measurements for the experimental arrangement used here.

Abstract: The propagating beam method utilizes discrete Fourier transforms for generating configuration-space solutions to optical waveguide problems without reference to modes. The propagating beam method can also give a complete description of the field in terms of modes by a Fourier analysis with respect to axial distance of the computed fields. Earlier work dealt with the accurate determination of mode propagation constants and group delays. In this paper the method is extended to the computation of mode eigenfunctions. The method is efficient, allowing generation of a large number of eigenfunctions from a single propagation run. Computations for parabolic-index profiles show excellent agreement between analytic and numerically generated eigenfunctions.

Abstract: The principles of measuring currents in high-voltage lines by magnetooptical means are described. Particular attention is payed to using an optical fiber both as a transmission line and a measuring sensor. The influence of birefringence on the measuring signal is discussed.