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Showing papers in "Applied Optics in 1982"


Journal ArticleDOI
TL;DR: Iterative algorithms for phase retrieval from intensity data are compared to gradient search methods and it is shown that both the error-reduction algorithm for the problem of a single intensity measurement and the Gerchberg-Saxton algorithm forThe problem of two intensity measurements converge.
Abstract: Iterative algorithms for phase retrieval from intensity data are compared to gradient search methods. Both the problem of phase retrieval from two intensity measurements (in electron microscopy or wave front sensing) and the problem of phase retrieval from a single intensity measurement plus a non-negativity constraint (in astronomy) are considered, with emphasis on the latter. It is shown that both the error-reduction algorithm for the problem of a single intensity measurement and the Gerchberg-Saxton algorithm for the problem of two intensity measurements converge. The error-reduction algorithm is also shown to be closely related to the steepest-descent method. Other algorithms, including the input-output algorithm and the conjugate-gradient method, are shown to converge in practice much faster than the error-reduction algorithm. Examples are shown.

5,210 citations


Journal ArticleDOI
TL;DR: Several workers have recently proposed digital techniques for high-resolution imaging through the turbulent atmosphere to calculate and average phase angles of a series of image Fourier transforms to suppress the unwanted atmospheric effects on image resolution.
Abstract: Several workers have recently proposed digital techniques for high-resolution imaging through the turbulent atmosphere. The basic concept of these algorithms is to calculate and average phase angles of a series of image Fourier transforms to suppress the unwanted atmospheric effects on image resolution. Since computed phase angles contain the ambiguities of integral multiples of 2 pirad, it is necessary to obtain continuous phase curves without the ambiguities before averaging. This process of eliminating the ambiguities is called phase tracking or unwrapping. A similar problem has been discussed by Oppenheim and Schafer and Tribolet in the context of realization of a certain homomorphic signal processing system.

673 citations


Journal ArticleDOI
TL;DR: Two modes have been launched into a conventional 10-m long multimode graded-index optical fiber using spatial filtering techniques and modular multiplexing appears to be possible over short fiber lengths.
Abstract: Two modes have been launched into a conventional 10-m long multimode graded-index optical fiber using spatial filtering techniques. The measured cross talk between the two modes in the baseband is -20 dB at the output end of the fiber. Modal multiplexing thus appears to be possible over short fiber lengths.

434 citations


Journal ArticleDOI
TL;DR: In this article, the authors derived theoretical results for noise in cryogenic bolometers and showed that Johnson noise is reduced by as much as 60% by electrothermal feedback from the bias supply.
Abstract: New theoretical results for noise in cryogenic bolometers are derived. Johnson noise is reduced by as much as 60% by electrothermal feedback from the bias supply. Phonon noise in the thermal link is reduced by as much as 30% relative to the usual equilibrium formula. Photon noise in the Rayleigh-Jeans limit is computed with attention to the attenuation of the photon correlations in the light beam. Basic results on bolometer responsivity, time constant, and thermal properties are presented in a new and convenient form. Excess 1/f and contact shot noise are also discussed.

386 citations


Journal ArticleDOI
TL;DR: A theoretical model for the laser-induced thermal lens effect in weakly absorbing media is derived and some experimental results which support the validity of this approach are presented.
Abstract: A theoretical model for the laser-induced thermal lens effect in weakly absorbing media is derived. The model predicts the intensity variation in the far field of the laser beam in the presence of the lensing medium and takes into account the aberrant nature of the thermal lens. Some experimental results which support the validity of this approach are presented.

350 citations


Journal ArticleDOI
TL;DR: Experimental results with simple photographic objects show that targets with different locations and orientations can be simultaneously recognized by the optical system.
Abstract: Presented in this paper is an optical implementation of a shift- and rotation-invariant pattern recognition technique. A computer-generated hologram is designed to match with one of the circular harmonic components of the target. Experimental results with simple photographic objects show that targets with different locations and orientations can be simultaneously recognized by the optical system.

323 citations


Journal ArticleDOI
TL;DR: A new method has been developed for rotation-invariant pattern recognition using one component of the circular harmonic expansion of the target in the preparation of the reference by FFT and multiplication in the frequency domain.
Abstract: A new method has been developed for rotation-invariant pattern recognition. One component of the circular harmonic expansion of the target is used in the preparation of the reference. Correlations between the input and reference objects are accomplished by FFT and multiplication in the frequency domain. In an experience with targets from an image with 192 × 192 pixels, target orientations were detected with an accuracy of ~0.1°. This method is also suitable for optical implementation.

272 citations


Journal ArticleDOI
TL;DR: A new method for tracing rays through graded-index media by transforming the ray equation into a convenient form and solving the resulting equation using a standard numerical technique is presented.
Abstract: A new method for tracing rays through graded-index media is presented. The method essentially consists of transforming the ray equation into a convenient form and solving the resulting equation using a standard numerical technique. A detailed comparison of this method with existing methods has also been made, and it is shown that for obtaining a desired accuracy this method requires much less computational effort.

269 citations


Journal ArticleDOI
TL;DR: The Rosencwaig-Gersho equation for the photoacoustic signal is recast in a manner that emphasizes the crucial role thermal wave interference plays in the production of the photoACoustic signal.
Abstract: The Rosencwaig-Gersho equation for the photoacoustic signal is recast in a manner that emphasizes the crucial role thermal wave interference plays in the production of the photoacoustic signal. This formalism is then used to suggest a technique for extracting thermal information from the structure in the photoacoustic signal resulting from thermal wave interference. Experimental measurements illustrating this technique are presented.

248 citations


Journal ArticleDOI
Darwin L. Wood1, Kurt Nassau1
TL;DR: The optical transmission and indices of refraction for the cubic isomorph of ZrO(2) stabilized with 12.0-mol % Y( 2)O(3) were measured at various temperatures and for a range of wavelengths from 0.36 to 5.1 microm.
Abstract: The optical transmission and indices of refraction for the cubic isomorph of ZrO2 stabilized with 12.0-mol % Y2O3 were measured at various temperatures and for a range of wavelengths from 0.36 to 5.1 μm. Index data to ±5 × 10−5 were fitted to a three-term Sellmeier equation. The value of ND = 2.15847. The dispersion NG − NB = 0.06044, while that for NC − NF = 0.03455. The temperature coefficient of the refractive index between 20 and 130°C varies from 1.6 × 10−5/K for 0.36-μm radiation to 0.62 × 10−5/K for 1.6-μm radiation.

247 citations


Journal ArticleDOI
Dietrich Marcuse1
TL;DR: For typical fibers the leakage loss of the HE(11) mode begins to increase significantly when the radius of curvature of the fiber axis reaches the 1-10-cm range.
Abstract: The loss increase of the HE(11) mode of a doubly clad (depressed-index) fiber due to constant curvature is considered. The calculations presented in this paper are based on a simplified theory. We find that for typical fibers the leakage loss of the HE(11) mode begins to increase significantly when the radius of curvature of the fiber axis reaches the 1-10-cm range.

Journal ArticleDOI
TL;DR: High-sensitivity measurements of infrared absorptions due to isolated lines broadened by air at atmospheric pressure are reported, and techniques for further increasing sensitivity are discussed.
Abstract: High-sensitivity measurements of infrared absorptions due to isolated lines broadened by air at atmospheric pressure are reported. Tunable diode lasers and harmonic techniques were employed to detect absorptions as small as 0.01% over path lengths up to 250 m through the open air. The limiting noise source is caused by a base line signal which varies with the optical alignment. The reported sensitivity is not a fundamental limit. Techniques for further increasing sensitivity are discussed.

Journal ArticleDOI
TL;DR: This paper combines fiber-coupling fundamentals, classical optics, and diffraction theory to provide a compact description of coupling efficiency that includes the effects of aberrations, fiber misalignments, and fiber-mode mismatch.
Abstract: Many single-mode fiber components include some form of optics, such as lenses or mirrors, for collecting light from a source fiber or laser and concentrating it on a receiving fiber. For such components there is a direct and simple relationship between coupling efficiency and optical aberrations. This paper combines fiber-coupling fundamentals, classical optics, and diffraction theory to provide a compact description of coupling efficiency that includes the effects of aberrations, fiber misalignments, and fiber-mode mismatch.


Journal ArticleDOI
TL;DR: For a multilayer structure illuminated by a laser beam, absorption of optical energy in the absorptive layers and the diffusion of the resultant heat throughout the structure are studied.
Abstract: For a multilayer structure illuminated by a laser beam, absorption of optical energy in the absorptive layers and the diffusion of the resultant heat throughout the structure are studied. Analytical and numerical procedures for this study are described, and, as a specific example, the profiles of temperature distribution during recording on a magnetooptical disk are presented. The technique is also expected to be of value for studies of thermal marking and laser annealing.

Journal ArticleDOI
TL;DR: A compact vacuum ultraviolet spectrometer system has been developed to provide time-resolved impurity spectra from tokamak plasmas and its sensitivity is comparable with that of a conventional grazing-incidence monochromator.
Abstract: A compact vacuum ultraviolet spectrometer system has been developed to provide time-resolved impurity spectra from tokamak plasmas. Two interchangeable aberration-corrected toroidal diffraction gratings with flat focal fields provide simultaneous coverage over the ranges 100–1100 A or 160–1700 A. The detector is an intensified self-scanning photodiode array. Spectral resolution is 2 A with the higher dispersion grating. Minimum readout time for a full spectrum is 20 msec, but up to seven individual spectral lines can be measured with a 1-msec time resolution. The sensitivity of the system is comparable with that of a conventional grazing-incidence monochromator.

Journal ArticleDOI
TL;DR: This paper presents a new development of the distributed-index planar microlens of 2.5-3-mm focal length and 0.15 N.A. and shows that it is usable with optical components in fiber communications and proposes a concept of stacked planar optics consisting of a stack of arrayed planarmicrolenses and other optical components.
Abstract: In this paper we present a new development of the distributed-index planar microlens of 2.5-3-mm focal length and 0.15 N.A. and also show that it is usable with optical components in fiber communications. We then propose a concept of stacked planar optics consisting of a stack of arrayed planar microlenses and other optical components. From this configuration a 2-D array of optical devices is monolithically available, and many discrete components can be separated from the array. An optical tap array has been fabricated as an example of stacked planar optics.

Journal ArticleDOI
TL;DR: The absorptions of pure and codoped germanium silicate preforms made by modified chemical vapor deposition (MCVD) have been studied from 170 to 400 nm, and the GeO content is found to increase with processing temperature, because higher temperature allows the greater dissociation of GeO(2) to GeO.
Abstract: The absorptions of pure and codoped germanium silicate preforms made by modified chemical vapor deposition (MCVD) have been studied from 170 to 400 nm. Three bands with maxima at 185, 242, and 325 nm have been observed. The shortest wavelength band is attributed to GeO2, while the other bands are assigned to GeO. The 242- and 325-nm bands are correlated with a singlet–singlet and a triplet–singlet transition of GeO, respectively. The GeO content is found to increase with processing temperature, because higher temperature allows the greater dissociation of GeO2 to GeO. The amount of GeO incorporated is determined to be of the order of 10−2 wt. %. The 325-nm band of GeO should have no effect on fiber loss in the IR region.

Journal ArticleDOI
TL;DR: A method of automatic determination of the complex refractive index and thickness of a layer which includes systematic measurement of the degree of inhomogeneity which is represented by a simple model is proposed.
Abstract: The refractive index of a layer is a sensitive function of the preparation conditions. Normal incidence measurement of the optical properties can reveal possible inhomogeneity of index. We propose a method of automatic determination of the complex refractive index and thickness of a layer which includes systematic measurement of the degree of inhomogeneity which is represented by a simple model. The usefulness of the technique is demonstrated by examples that form part of an experimental study of a number of useful optical materials including Y2O3, TiO2, MgF2, HfO2, and SiO2. The dispersions of the refractive index, the extinction coefficient, and of the inhomogeneity are represented by Cauchy formulas with accurately determined coefficients. The results can therefore be readily used in computing the optical properties of thin-film multilayers.

Journal ArticleDOI
Q. Cai1, Kuo-Nan Liou1
TL;DR: A scattering model involving complete polarization information for arbitrarily oriented hexagonal columns and plates is developed on the basis of the ray tracing principle which includes contributions from geometric reflection and refraction and Fraunhofer diffraction.
Abstract: A scattering model involving complete polarization information for arbitrarily oriented hexagonal columns and plates is developed on the basis of the ray tracing principle which includes contributions from geometric reflection and refraction and Fraunhofer diffraction. We present a traceable and analytic procedure for computation of the scattered electric field and the associated path length for rays undergoing external reflection, two refractions, and internal reflections. We also derive an analytic expression for the scattering electric field in the limit of Fraunhofer diffraction due to an oblique hexagonal aperture. Moreover the theoretical foundation and procedures are further developed for computation of the scattering phase matrix containing 16 elements for randomly oriented hexagonal crystals. Results of the six independent scattering phase matrix elements for randomly oriented large columns and small plates, having length-to-radius ratios of 300/60 and 8/10 microm, respectively, reveal a number of interesting and pronounced features in various regions of the scattering angle when a visible wavelength is utilized in the ray tracing program. Comparisons of the computed scattering phase function, degree of linear polarization, and depolarization ratio for randomly oriented columns and plates with the experimental scattering data obtained by Sassen and Liou for small plates are carried out. We show that the present theoretical results within the context of the geometric optics are in general agreement with the laboratory data, especially for the depolarization ratio.

Journal ArticleDOI
TL;DR: The effects of multiple scattering on the interpretation of the time dependence of elastic backscattering of laser pulses from the ocean (lidar) are investigated through solving the radiative transfer equation by Monte Carlo techniques.
Abstract: The effects of multiple scattering on the interpretation of the time dependence of elastic backscattering of laser pulses from the ocean (lidar) are investigated through solving the radiative transfer equation by Monte Carlo techniques. In particular, after removal of the geometric loss factors, it is found that the backscat-tered power is a decaying exponential function of time, over the time interval required for photons to travel four attenuation lengths through the water. The effective attenuation coefficient of this exponential decay is found to be strongly dependent on the parameters of the lidar system and on the optical properties of the water. The significant parameter is the ratio of the radius of the spot on the sea surface viewed by the lidar receiver optics to the mean free path of photons in the water. For values of this parameter near zero, the decay is determined by the beam attenuation coefficient, while for values greater than ~5-6, the decay is given by the attenuation coefficient for downwelling irradiance, often referred to as the diffuse attenuation coefficient. Between these two extremes the interpretation of the effective attenuation coefficient requires, essentially, complete knowledge of the inherent optical properties of the water: the beam attenuation coefficient and the volume scattering function.

Journal ArticleDOI
TL;DR: A general mathematical framework for simulating processes in heterogeneous 3-D scenes is presented and a model designed and coded for application to radiative transfers in vegetative scenes was shown to follow known physical principles of radiative transfer.
Abstract: A general mathematical framework for simulating processes in heterogeneous 3-D scenes is presented. Specifically, a model was designed and coded for application to radiative transfers in vegetative scenes. The model is unique in that it predicts (1) the directional spectral reflectance factors as a function of the sensor's azimuth and zenith angles and the sensor's position above the canopy, (2) the spectral absorption as a function of location within the scene, and (3) the directional spectral radiance as a function of the sensor's location within the scene. The model was shown to follow known physical principles of radiative transfer. Initial verification of the model as applied to a soybean row crop showed that the simulated directional reflectance data corresponded relatively well in gross trends to the measured data. However, the model can be greatly improved by incorporating more sophisticated and realistic anisotropic scattering algorithms

Journal ArticleDOI
TL;DR: In this article, the authors describe the development of an aethalometer that can measure aerosol absortion in real time, which can be used for real-time analysis.
Abstract: The authors describe the development of an aethalometer. This portable device measures aerosol absortion in real time. (AIP)


Journal ArticleDOI
TL;DR: The usefulness of the SiO(2)-Si(3)N(4) system for gradient-index optics has been investigated and Preparation techniques are discussed.
Abstract: The usefulness of the SiO2–Si3N4 system for gradient-index optics has been investigated. Dispersion data, temperature dependence of the refractive index, and physical properties are presented. Preparation techniques are discussed.

Journal ArticleDOI
TL;DR: Equations giving the intensity, the divergence, and the radius of the modified beam are derived in simple practical form for experimentalists and show that, even in the case of negligible power losses through the aperture, the diffracted beam characteristics may appreciably differ from those of the incident beam.
Abstract: A Gaussian beam weakly diffracted by a circular aperture can be approximated in the far field by another Gaussian beam with slightly different characteristics. Equations giving the intensity, the divergence, and the radius of the modified beam are derived in simple practical form for experimentalists. These approximated formulas show that, even in the case of negligible power losses through the aperture, the diffracted beam characteristics may appreciably differ from those of the incident beam. In a first approximation, diffraction effects may be ignored only if the ratio a/r(0) of the aperture radius a to the l/e intensity beam radius r(0) in the aperture plane is larger than 3.

Journal ArticleDOI
TL;DR: A new liquid crystal light valve (LCLV) is presented using bulk monocrystalline Bi(12)SiO(20) (BSO) as both the photoconductive material and as one of the substrates supporting the liquid crystal layer.
Abstract: A new liquid crystal light valve (LCLV) is presented using bulk monocrystalline Bi12SiO20 (BSO) as both the photoconductive material and as one of the substrates supporting the liquid crystal layer. The photoconductive properties of the BSO under ac voltages are investigated. The device operates at room temperature with a low ac drive voltage (25-V ac at 500 Hz). These specific properties are explained from the aspect of an equivalent electrical circuit of the structure. A prototype BSO LCLV with a 15-μm liquid crystal thickness shows a 10-lp mm−1 spatial resolution. The device coherent modulation transfer function was measured experimentally and found to agree with theory. Typical writing energies are ~20 μJ cm−2 at wavelength λ = 450 nm.

Journal ArticleDOI
TL;DR: Mode conversion and radiation loss in integrated-optic tapers and Y-junctions are calculated by means of the beam propagation method combined with the effective refractive-index method.
Abstract: Mode conversion and radiation loss in integrated-optic tapers and Y-junctions are calculated by means of the beam propagation method combined with the effective refractive-index method. Simple design rules for the tapers and Y-junctions are derived from the obtained results.

Journal ArticleDOI
TL;DR: The sum- and difference-frequency conversion will provide intense coherent VUV light continuously tunable between 1100 and 2100 A.
Abstract: Nonresonant sum- and difference-frequency mixing of the fundamental omega(L) and the second harmonic omega(UV) radiation of a powerful narrowband pulsed dye laser system excited by an Nd:YAG laser (lambda(L) = 5500-6500 A) generates intense VUV radiation in krypton and xenon with the frequency omega(VUV) = 2omega(UV) micro omega(L) The sum-frequency is tunable in spectral regions of negative dispersion between 1100 and 1300 A The maximum VUV pulse power exceeds 20 W (5 x 10(10) photons/pulse) VUV light pulses with up to 60 W (23 x 10(11) photons/pulse) are provided by the difference-frequency at wavelengths between 1850 and 2070 A In addition the conversion process omega(VUV) = 2omega(UV) - omega(IR) (omega(IR) is the frequency of the Nd:YAG laser) generates radiation in the wavelength range of 1595-1866 A With present laser systems the tuning range of the difference-frequency could be extended to wavelengths as short as 1226 A The sum- and difference-frequency conversion will thus provide intense coherent VUV light continuously tunable between 1100 and 2100 A

Journal ArticleDOI
Gadi Eisenstein1, D Vitello1
TL;DR: A simple method to selectively etch a fiber end to produce a conical lens whose base coincides with the fiber core is proposed and it is found that high coupling efficiency is expected in cases of practical interest.
Abstract: Coupling efficiency between a laser diode and a single-mode fiber can be greatly increased by using a lensing scheme to match their respective modes. We propose a simple method to selectively etch a fiber end to produce a conical lens whose base coincides with the fiber core. If needed, this lens may be fire polished or arc melted into a hemispherical lens of the same diameter. We present a general theoretical design of both these lenses. We find that high coupling efficiency is expected in cases of practical interest. Initial experimental results are reported in which coupling losses as low as 3 dB were obtained.