Showing papers in "Applied Optics in 1988"

Numerically stable algorithm for discrete-ordinate-method radiative transfer in multiple scattering and emitting layered media.

Abstract: The transfer of monochromatic radiation in a scattering, absorbing, and emitting plane-parallel medium with a specified bidirectional reflectivity at the lower boundary is considered. The equations and boundary conditions are summarized. The numerical implementation of the theory is discussed with attention given to the reliable and efficient computation of eigenvalues and eigenvectors. Ways of avoiding fatal overflows and ill-conditioning in the matrix inversion needed to determine the integration constants are also presented.

Curvature sensing and compensation: a new concept in adaptive optics.

Abstract: Mesure et compensation, en temps reel, de fronts d'onde soumis a une perturbation atmospherique. Description d'un systeme a boucle fermee utilisant un miroir bimorphe

Technique for monolithic fabrication of microlens arrays

Abstract: A microlens fabrication process is described which can be used in applications requiring integration of optical elements (lenses) and microcircuits. The process is fully compatible with IC fabrication technology and uses commercially available IC processing materials. The obtained microlenses are of excellent quality and basically show diffraction-limited resolution with ~1-μm spot size. Extensions of the process to production of nonspherical lenses and use of alternative material packages are also discussed.

Guided-wave optoelectronics

Abstract: 1. Introduction..- 1.1 Overview.- 1.2 Organization of the Book.- References.- 2. Theory of Optical Waveguides. (With 32 Figures).- 2.1 Ray Optics of the Slab Waveguide.- 2.1.1 Refraction and Reflection.- 2.1.2 Guided Modes.- 2.1.3 The Goos-Hanchen Shift.- 2.1.4 Effective Guide Thickness.- 2.2 Fundamentals of the Electromagnetic Theory of Dielectric Waveguides.- 2.2.1 Maxwell's Equations.- 2.2.2 Modes of the Waveguide.- 2.2.3 The Wave Equations for Planar Guides.- 2.2.4 Mode Properties Following from Symmetry.- 2.2.5 Orthogonality of the Modes.- 2.2.6 Mode Expansion and Normalization.- 2.2.7 The Variation Theorem for Dielectric Waveguides.- 2.2.8 Power Flow and Stored Energy in a Dielectric Waveguide.- 2.2.9 Variational Properties of the Propagation Constant.- 2.3 Modes of the Planar Slab Guide.- 2.3.1 TE Modes.- 2.3.2 TM Modes.- 2.3.3 Multilayer Slab Guides.- 2.4 Planar Guides with Graded-Index Profiles.- 2.4.1 The Parabolic Profile (Harmonic Oscillator).- 2.4.2 The "1/cosh2" Profile.- 2.4.3 The Exponential Profile.- 2.4.4 Index Profiles with Strong Asymmetry.- 2.4.5 The WKB Method.- 2.5 Channel Waveguides.- 2.5.1 Channel Guide Geometries.- 2.5.2 The Vector Wave Equation.- 2.5.3 Numerical Analysis.- 2.5.4 Separation of Variables.- 2.5.5 The Method of Field Shadows.- 2.5.6 The Vector Perturbation Theorem.- 2.5.7 The Effective-Index Method.- 2.6 Coupled-Mode Formalism and Periodic Waveguides.- 2.6.1 Excitation of Waveguide Modes.- 2.6.2 Waveguide Deformations.- 2.6.3 Coupled-Wave Solutions.- 2.6.4 Periodic Waveguides.- 2.6.5 TE-to-TM Mode Conversion.- References.- 3. Waveguide Transitions and Junctions (With 43 Figures).- 3.1 Waveguide Modes and Coupled-Mode Theory.- 3.1.1 Normal Modes of Coupled Waveguides.- 3.1.2 Coupled-Mode Theory Representation.- 3.2 Fast and Slow Transitions.- 3.2.1 Local Normal Modes.- 3.2.2 Adiabatic Transition.- 3.2.3 Abrupt Transition.- 3.2.4 Tapered Velocity Coupler.- 3.2.5 3 dB Coupler.- 3.2.6 Directional Coupler.- 3.3 Mode Coupling Between Local Normal Modes.- 3.3.1 Coupled-Amplitude Equations.- 3.3.2 Differential Form of Coupled-Amplitude Equations.- 3.3.3 Coupled-Mode Theory Representation of Cij.- 3.4 Two-Arm Branches.- 3.4.1 Step Approximation for a Waveguide Branch.- 3.4.2 Analytic Solution for Shaped Branches.- 3.4.3 Experimental Results.- 3.4.4 Superposition of Solutions.- 3.5 Waveguide Horns.- 3.5.1 Mode-Conversion Coefficient Cij for Channel Waveguides.- 3.5.2 Approximation for ??ij.- 3.5.3 Approximation for Cij.- 3.5.4 Parabolic Solution.- 3.6 Branches with Three Arms.- 3.6.1 Normal Modes of Three Coupled Waveguides.- 3.6.2 3 X 2 Waveguide Coupler.- 3.7 Conclusion.- References.- 4. Titanium-Diffused Lithium Niobate Waveguide Devices (With 39 Figures).- 4.1 Waveguide Fabrication.- 4.1.1 Titanium Diffused Waveguides.- 4.1.2 Proton Exchange LiNbO3 Waveguides.- 4.1.3 Post-Waveguide Processing.- 4.2 Basic Device Considerations.- 4.2.1 Electro-Optic Effect.- 4.2.2 Phase Modulator.- 4.2.3 Insertion Loss.- 4.2.4 Voltage/Loss Tradeoffs: Waveguide Tailoring.- 4.3 Switch/Modulator.- 4.3.1 Directional Coupler.- 4.3.2 Balanced-Bridge Interferometer.- 4.3.3 Intersecting-Waveguide Switch.- 4.4 On/Off Modulators.- 4.4.1 Y-Branch Interferometer.- 4.4.2 Voltage and Bandwidth Consideration for Switch/ Modulators.- 4.5 Polarization Devices.- 4.5.1 TE - TM Conversion.- 4.5.2 Polarization Controller.- 4.5.3 Polarization-Selective Devices.- 4.6 Wavelength Filters.- 4.6.1 Interferometric Filters.- 4.6.2 Coupled-Mode Filters.- 4.7 Polarization-Insensitive Devices.- 4.8 Some Ti:LiNbO3 Integrated-Optic Circuits.- 4.8.1 Coherent Lightwave Receiver.- 4.8.2 Optical Switch Arrays.- 4.9 Applications.- 4.9.1 External Modulators.- 4.9.2 High-Speed Analog to Digital Conversion.- 4.9.3 Fiber Gyroscope Chip.- References.- 5. Mode-Controlled Semiconductor Lasers (With 55 Figures).- 5.1 Organization of the Chapter.- 5.1.1 Notation.- 5.2 Laser Basics.- 5.2.1 Epitaxial Materials and Heterostructure.- 5.2.2 Waveguide Propagation, Amplification and Oscillation.- 5.2.3 Laser Gain.- 5.2.4 Spontaneous Emission.- 5.2.5 Photon Rate Equation.- 5.2.6 Spectral Hole Burning.- 5.2.7 Carrier Injection in a Heterojunction.- 5.2.8 Modal Rate Equations.- 5.2.9 Longitudinal Variation of Photon Density.- 5.2.10 Steady-State Solution of Rate Equations.- 5.2.11 Measurement of Modal Reflectivity and Laser Gain.- 5.3 Structures for Transverse-Mode Control.- 5.3.1 Stripe Geometry Laser, Blocking Layer.- 5.3.2 Buried Heterostructure Lasers.- 5.3.3 Ridge Waveguide Lasers.- 5.4 Longitudinal Mode Control.- 5.4.1 Three- and Four-Mirror Resonators.- 5.4.2 Distributed Bragg Gratings.- 5.4.3 Semiconductor DFB Lasers.- 5.4.4 DBR and Phase-Slip DFB Lasers.- 5.5 Linewidth.- 5.5.1 Linewidth of Fabry-Perot Laser.- 5.5.2 Linewidth Reduction Using Extended Cavities.- 5.6 High-Speed Modulation.- 5.6.1 Modulation Response.- 5.6.2 Origin of Chip Parasitics.- 5.6.3 Evaluation of Parasitics.- 5.6.4 Dependence of Parasitics on Device Structure.- 5.6.5 The Intrinsic Laser - Small-Signal Intensity Modulation Response.- 5.6.6 High-Frequency Limitations.- 5.6.7 Design Considerations for Wideband Lasers.- 5.6.8 Large-Signal Modulation - PCM.- 5.6.9 Large-Signal Modulation - Gain Switching.- 5.6.10 Active Mode-Locking.- 5.7 Luminescent Diodes and Laser Amplifiers.- 5.7.1 Edge-Emitting and Superluminescent Diodes.- 5.7.2 Linear Amplification and Amplified Spontaneous Emission in TWAs and ELEDs.- 5.7.3 Fabry-Perot Amplifiers and ELEDs.- 5.7.4 Amplifier Gain Compression.- 5.7.5 Receiver Noise.- 5.8 Tunable and FM Lasers.- 5.8.1 Tunable DBR.- 5.8.2 Tunable DFB.- Appendix 5A: Glossary of Symbols.- References.- 6. Semiconductor Integrated Optic Devices (With 66 Figures).- 6.1 Semiconductor Waveguide Theory.- 6.1.1 Methods of Index Change in Semiconductors.- 6.1.2 Slab Waveguides.- 6.1.3 Channel Waveguides.- 6.1.4 Coupling Effects.- 6.1.5 Optical Loss.- 6.1.6 Curvature Loss.- 6.2 Material Technology.- 6.2.1 Liquid Phase Epitaxy (LPE).- 6.2.2 Vapor Phase Epitaxy (VPE).- 6.2.3 Metal Organic Chemical Vapor Deposition (MOCVD).- 6.2.4 Molecular Beam Epitaxy (MBE).- 6.2.5 Summary.- 6.3 Passive Waveguide Devices - Fabrication and Characterization.- 6.3.1 Channel Waveguides.- 6.3.2 Couplers.- 6.3.3 Bends and Branches.- 6.3.4 Grating Filter.- 6.4 Electro-Optic Guided-Wave Modulators - Theory.- 6.4.1 Electro-Optic Effect in III-V Semiconductors.- 6.4.2 Modulator Design.- 6.4.3 Modulation Frequency Analysis.- 6.4.4 Traveling-Wave Phase Modulators.- 6.4.5 TE-TM Coupling Analysis.- 6.4.6 Infrared Waveguide Modulators - Wavelength Scaling.- 6.4.7 Electro-Absorption Modulation.- 6.4.8 Carrier-Injection Modulator.- 6.4.9 Nonlinear Waveguide Modulator.- 6.5 Electro-Optic Guided-Wave Modulator Characteristics.- 6.5.1 Phase Modulators.- 6.5.2 Directional-Coupler Switches.- 6.5.3 Interferometric Modulators.- 6.5.4 Integrated Waveguides/Optoelectronics/Electronics.- 6.5.5 Electro-Absorption Modulators.- 6.5.6 Multiple-Quant urn-Well Modulators.- 6.5.7 Nonlinear Waveguide Modulators.- 6.6 Optoelectronic Integrated Circuits (OEIC).- 6.7 Concluding Remarks.- References.- 7. Recent Advances (With 1 Figure).- 7.1 Introduction.- 7.2 Theory of Optical Waveguides.- 7.3 Waveguide Transitions and Junctions.- 7.4 Titanium-Diffused Lithium Niobate Waveguide Devices.- 7.5 Mode-Controlled Semiconductor Lasers.- 7.6 Semiconductor Integrated Optic Devices.- References.

Adaptive optical networks using photorefractive crystals.

Abstract: The capabilities of photorefractive crystals as media for holographic interconnections in neural networks are examined. Limitations on the density of interconnections and the number of holographic associations which can be stored in photorefractive crystals are derived. Optical architectures for implementing various neural schemes are described. Experimental results are presented for one of these architectures.

Comparison between optical and electrical interconnects based on power and speed considerations

Abstract: Conditions are determined for which optical interconnects can transmit information at a higher data rate and consume lc3s power than the equivalent electrical interconnections. The analysis is performed for free-space optical intrachip communication links. Effects of scaling circuit dimensions, presence of signal fan-out, and the use of light modulators as optical signal transmitters are also discussed.

Radiometric calibration of IR Fourier transform spectrometers: solution to a problem with the High-Resolution Interferometer Sounder.

Abstract: A calibrated Fourier transform spectrometer, known as the High-Resolution Interferometer Sounder (HIS), has been flown on the NASA U-2 research aircraft to measure the infrared emission spectrum of the earth. The primary use - atmospheric temperature and humidity sounding - requires high radiometric precision and accuracy (of the order of 0.1 and 1 C, respectively). To meet these requirements, the HIS instruments, the HIS instrument performs inflight radiometric calibration, using observations of hot and cold blackbody reference sources as the basis for two-point calibrations at each wavenumber. Initially, laboratory tests revealed a calibration problem with brightness temperature errors as large as 15 C between 600 and 900/cm. The symptom of the problem, which occurred in one of the three spectral bands of HIS, was a source-dependent phase response. Minor changes to the calibration equations completely eliminated the anomalous errors. The new analysis properly accounts for the situation in which the phase response for radiance from the instrument itself differs from that for radiance from an external source. The mechanism responsible for the dual phase response of the HIS instrument is identified as emission from the interferometer beam splitter.

Intensity images and statistics from numerical simulation of wave propagation in 3-D random media

Abstract: An extended random medium is modeled by a set of 2-D thin Gaussian phase-changing screens with phase power spectral densities appropriate to the natural medium being modeled. Details of the algorithm and limitations on its application to experimental conditions are discussed, concentrating on power-law spectra describing refractive-index fluctuations of the neutral atmosphere. Inner and outer scale effects on intensity scintillation spectra and intensity variance are also included. Images of single realizations of the intensity field at the observing plane are presented, showing that under weak scattering the small-scale Fresnel length structure of the medium dominates the intensity scattering pattern. As the strength of scattering increases, caustics and interference fringes around focal regions begin to form. Finally, in still stronger scatter, the clustering of bright regions begins to reflect the large-scale structure of the medium. For plane waves incident on the medium, physically reasonable inner scales do not produce the large values of intensity variance observed in the focusing region during laser propagation experiments over kilometer paths in the atmosphere. Values as large as experimental observations have been produced in the simulations, but they require inner scales of the order of 10 cm. Inclusion of an outer scale depresses the low-frequency end of the intensity spectrum and reduces the maximum of the intensity variance. Increasing the steepness of the power law also slightly increases the maximum value of intensity variance.

Exact Rayleigh scattering calculations for use with the Nimbus-7 Coastal Zone Color Scanner

Abstract: For improved analysis of Coastal Zone Color Scanner (CZCS) imagery, the radiance reflected from a planeparallel atmosphere and flat sea surface in the absence of aerosols (Rayleigh radiance) has been computed with an exact multiple scattering code, i.e., including polarization. The results indicate that the single scattering approximation normally used to compute this radiance can cause errors of up to 5% for small and moderate solar zenith angles. At large solar zenith angles, such as encountered in the analysis of high-latitude imagery, the errors can become much larger, e.g.,>10% in the blue band. The single scattering error also varies along individual scan lines. Comparison with multiple scattering computations using scalar transfer theory, i.e., ignoring polarization, show that scalar theory can yield errors of approximately the same magnitude as single scattering when compared with exact computations at small to moderate values of the solar zenith angle. The exact computations can be easily incorporated into CZCS processing algorithms, and, for application to future instruments with higher radiometric sensitivity, a scheme is developed with which the effect of variations in the surface pressure could be easily and accurately included in the exact computation of the Rayleigh radiance. Direct application of these computations to CZCS imagery indicates that accurate atmospheric corrections can be made with solar zenith angles at least as large as 65 degrees and probably up to at least 70 degrees with a more sensitive instrument. This suggests that the new Rayleigh radiance algorithm should produce more consistent pigment retrievals, particularly at high latitudes.

Optical properties of Al, Fe, Ti, Ta, W, and Mo at submillimeter wavelengths.

Abstract: Measurements of the optical constants of metals at submillimeter wavelengths are sparse. We have used a nonresonant cavity to measure, at room temperature, the angle averaged absorptance spectra P(omega) of aluminum, molybdenum, tantalum, titanium, tungsten, and iron in the 30-300-cm(-1) wavenumber region. The real part of the normalized surface impedance spectrum, z(omega) = r(omega) + ix(omega), was determined from P(omega). Measurements were also made on iron from 400 to 4000 cm(-1) using standard reflectance techniques. The r(omega) spectrum was combined with previous measurements by others at higher frequencies and Kramers-Kronig analyses of the resultant combined r(omega) spectra provided epsilon(omega) = epsilon(1)(omega) + iepsilon(2)(omega) and N(omega) = n(omega) + ik(omega).

Optical chemical sensor based on surface plasmon measurement.

Abstract: A new optical chemical sensor was developed for chemical sensing based on light-excited surface plasmon measurement. Concentration of the chemical species is found in liquid or gas without the help of a reagent but by measuring the resonance condition of the surface plasmon on the sensing metal surface. The resonance condition is given by the dielectric constant of the sample faced on the metal. The developed sensor can be compact and simple, because of the absence of mechanical moving parts, by using multichannel angular light intensity detection with a photodiode array and a Fourier transform optical setup. Experimental results are shown for measurement of ethanol concentration in water. The detection limit for ethanol in water was 10(-4) wt./wt. by the experiments with the developed system.

Fractal surface finish.

Abstract: Surface finish measurements are usually fitted to models of the finish correlation function which are parametrized in terms of root-mean-square roughnesses, σ, and correlation lengths, l. Highly finished optical surfaces, however, are frequently better described by fractal models, which involve inverse power-law spectra and are parametrized by spectral strengths, Kn, and spectral indices, n. Analyzing measurements of fractal surfaces in terms of σ and l gives results which are not intrinsic surface parameters but which depend on the bandwidth parameters of the measurement process used. This paper derives expressions for these pseudoparameters and discusses the errors involved in using them for the characterization and specification of surface finish.

Hybrid diffractive-refractive lenses and achromats

Abstract: Hybrid elements containing optical power with both diffractive (holographic) and refractive components are shown to be useful for obtaining arbitrary or, in special cases, achromatic dispersive characteristics. In one configuration a volume holographic element is coated on the surface of a crown glass lens, and by varying the power distributions among the refractive and holographic components while maintaining constant overall optical power the effective Abbe V numbers of the resultant hybrid element are shown to span all real numbers excepting a narrow interval around zero. In the achromat case (V number = ∞), both refractive and diffractive components are of the same sign resulting in much smaller glass curvatures than in all-refractive achromat doublets or apochromat triplets. The large separation between holographic partial dispersions and available glass partial dispersions is shown to lead to hybrid three-color achromats with greatly reduced glass curvatures. Applications are expected to include broadband achromatic objectives and chromatic aberration corrector plates in high performance optical systems. Such corrector plates may have any net power (including zero) while exhibiting effective V numbers that are positive or negative and that span a wide range, e.g., ±1 or ±1000. Further advantages include reducing the need for choosing high dispersion glasses, which may be costly and difficult to grind or polish. High diffraction efficiency and broad spectral bandwidths (in excess of 3000 A) are obtained in the holographic optical elements using single-element central-stop and cascaded element designs.

Laser-induced fluorescence with tunable excimer lasers as a possible method for instantaneous temperature field measurements at high pressures: checks with an atmospheric flame

Abstract: A new method for instantaneous temperature field measurements based on LIF studies of OH, O2, and H2O in an open atmospheric flame with a tunable excimer laser is suggested. In this method the crucial problem of quenching at higher pressures is almost completely eliminated by excitation to a fast predissociating state. The various possible excitation and fluorescence processes that can be induced in the narrow tuning range of the KrF laser are characterized experimentally by excitation and dispersion spectra for the three molecules OH, O2, and H2O. Of particular importance is the large power of the KrF laser, which allows efficient excitation of even weak transitions. The fast predissociation of these molecules in connection with the powerful excitation laser suggests that instantaneous temperature field measurements should be possible at higher pressures.

Noninvasive technique for oximetry of blood in retinal vessels.

Abstract: A noninvasive spectrophotometric technique for the measurement of oxygen saturation of the blood in discrete retinal vessels is described. The instrument, the retinal vessel oximeter, uses scanning fundus reflectometry to determine the optical density of a retinal vessel at three wavelengths (558, 569, and 586 nm). Oxygen saturation is determined after compensation for the effects of light scattering by the red blood cells by relating the measured densities with the corresponding extinction coefficients of oxyhemoglobin and deoxygenated hemoglobin. The vessel diameter is also measured continuously. All data acquisition and analysis are performed on-line by means of a microcomputer, and a vessel tracking system is used to compensate for the effects of eye movements. Oxygen saturation measurements for blood flowing through glass capillaries are presented as well as representative results of oxygen saturation measurements on normal human subjects.

Ranging and velocimetry signal generation in a backscatter-modulated laser diode.

Abstract: A compact self-aligning laser radar has been constructed for coheren ranging and velocimetry using a laser diode modulated by feedback from light scattered from a diffusing target. The phenomenology of beat-signal generation in the device is discussed from both experimental and theoretical points of view. The ac-coupled modulation waveform is asymmetric (similar to a sawtooth) and different for the two propagation directions of the light leaving the diode. Atheoreticalmodel, based on the mode structure ofathree-mirrorFabry-Perot cavity, describes signal generation in these experiments and accounts for the asymmetric waveform.

Coupling starlight into single-mode fiber optics.

Abstract: We have calculated the efficiency with which starlight can be coupled into a single-mode fiber optic that is placed in the focal plane of a telescope. The calculations are performed for a wide range of seeing conditions, with and without rapid image stabilization, and for a wide range of wavelengths. The dependence of coupling efficiency on the f-ratio of the incident beam is explored. Also, we calculate the coupling efficiency as a function of displacement for a perfect Airy pattern. We have also used a computer program which simulates atmospheric wavefronts to determine the variance of instantaneous coupling efficiency as a function of seeing. In perfect conditions, the maximum efficiency at the LP(11) mode cutoff is 78% due to the mismatch of the Airy pattern and the nearly Gaussian mode of the fiber. Maximum total coupled power is attained at d/r(0) = 4 with rapid image stabilization.

Optical diffusion in layered media.

Abstract: In highly scattering media, light energy fluence rate distributions can be described by diffusion theory. Boundary conditions, appropriate to the diffusion approximation, are derived for surfaces where reflection of diffuse light occurs. Both outer surfaces and interfaces separating media with different indices of refraction can be treated. The diffusion equation together with its boundary conditions is solved using the finite element method. This numerical method allows much freedom of geometry.

Refractive index of solutions at high concentrations

Abstract: The refractive index of liquid solutions at the He–Ne laser wavelength, 0.6328 μm, is presented. The measurements were carried out using the conventional minimum deviation method of an equilateral hollow glass prism. The refractive indices of sucrose, sodium chloride, glucose, and caster sugar solutions for a range density varying from distilled water to a saturated condition were measured. The result shows that at higher of concentrations a slight curvature can be seen from the plot of refractive index vs concentration of solution. However, the refractive index of sucrose shows a linear relationship with concentration. The accuracy of the measurements is estimated to be better than 0.3%.

Scattering by irregular inhomogeneous particles via the digitized Green’s function algorithm

Abstract: The digitized Green’s function (DGF) algorithm and the underlying theory are described. This finite element algorithm models dielectric particles of arbitrary shape and arbitrary optical structure. DGF predictions of differential and total cross sections are compared with predictions of Mie and EBCM algorithms for several homogeneous spheres and spheroids. Results of tests of convergence of the DGF calculation as the number of elements are increased are presented. Computer time and storage requirements as functions of wavelength and particle size, shape, and optical structure are discussed.

Accuracy of phase shifting interferometry

Abstract: The accuracy of phase shifting interferometers is impaired by mechanical drifts and vibrations, intensity variations, nonlinearities of the photoelectric detection device, and, most seriously, by inaccuracies of the reference phase shifter. The phase shifting procedure enables the detection of most of the errors listed above by a special Lissajous display technique described here. Furthermore, it is possible to correct phase shifter inaccuracies by using an iterative process relying solely on the interference pattern itself and the Fourier sums used in phase shifting interferometry.

Comparison of Mie theory and the light scattering of red blood cells

Abstract: Two important optical properties of red blood cells (RBCs), their microscopic scattering cross sections sigma(s), and the mean cosine of their scattering angles micro, contribute to the optical behavior of whole blood. Therefore, the ability of Mie theory to predict values of sigma(s) and was tested by experiment. In addition, the effect of red blood cell size on sigma(s) and micro was investigated in two ways: (1) by studying erythrocytes from the dog, goat, and human, three species known to have different RBC sizes and (2) by allowing the RBCs from each species to shrink or swell osmotically. Values of sigma(s) obtained by measuring the collimated transmittance of dilute RBC suspensions illuminated with a He-Ne laser agreed with those predicted by Mie theory. Moreover, measured as values were directly proportional to RBC volume. By contrast, values of from Mie theory were consistently greater than those obtained experimentally by making angular scattering measurements in a goniometer. Thus Mie theory appears to yield adequate values for the RBC's microscopic scattering cross section, but by treating the RBC as a sphere with an equal volume, Mie theory fails to take the RBC's anisotropy into account and thus yields spuriously high values for micro.

Three-dimensional imaging systems: a new development

Abstract: An optical system which produces 3-D images exhibiting continuous parallax with no flipping or cardboarding is described. Both integral and lenticular images can be recorded on photographic film without recourse to a specialized environment. Standard photographic processing and enlarging techniques are used to obtain hard copy. Measurements on commercially available retrodirective screens and a new retroscreen arrangement show that the new screen developed gives significant advantages. A retrodirective and a transmission version of the system have been constructed.

Three-dimensional beam-deflection optical tomography of a supersonic jet

Abstract: We report 3-D imaging of density in a supersonic expansion using beam-deflection optical tomography. Quantitative high-resolution images with absolute accuracy of 3%, dynamic range of 500:1, and spatial resolution to within a factor of 1.7 of the diffraction limit were produced with a He-Ne laser and simple apparatus. Theory shows that the spatial frequency content of beam-deflection measurements is well suited for tomographic reconstruction. The theory for the diffraction-limited resolution for tomography is presented.

Global-fit approach to the analysis of limb-scanning atmospheric measurements.

Abstract: A method for the retrieval of concentration profiles of atmospheric constituents from spectra, recorded by balloon-borne spectrometers with the limb-scanning technique, is presented. The method uses a nonlinear least-squares fit procedure to fit simultaneously the whole concentration profile on a limb-scanning sequence of spectra. A use in interferometric measurements of the stratospheric emission is shown and a comparison is discussed with the results obtained from the analysis of the same data set, by using the onion-peeling method in which the error propagation, over concentrations, is taken into account. With the global-fit, error bars smaller than with the onion-peeling analysis are obtained. Computational details are also discussed.

Simultaneous planar measurements of velocity and pressure fields in gas flows using laser-induced fluorescence.

Abstract: The development of a nonintrusive spectroscopic technique is reported which permits simultaneous spatially resolved measurements of two velocity components and pressure in a plane of a compressible gaseous flow field. The technique is based on the detection of fluorescence from an absorption line excited with a narrow-bandwidth laser. Doppler shift and pressure broadening of the line are exploited to extract velocity and pressure information, respectively. The fluorescence is detected at a 90° angle with an image-intensified 100 × 100 element photodiode-array camera which is interfaced with a laboratory computer. Results of the implementation in a Mach 1.5 underexpanded supersonic jet are presented.

Scattering of electromagnetic waves by composite spherical particles: experiment and effective medium approximations

Abstract: We have measured the differential scattering cross sections (phase functions I22) and the normalized extinction and scattering cross sections (efficiences) of composite spherical particles. The size parameter x = 2πr/λ was around 2π. Composite spheres consisted of nonabsorbing matrix containing a small amount (1.6 and 2.7% by volume) of highly absorbing inclusions. Such composite particles may represent a realistic model of fog or cloud droplets containing small amounts of carbon or a composite atmospheric aerosol particle. We have compared measured data with those calculated using seven different effective medium approximations. We have found that the approximations of Bruggeman and Maxwell Garnett, the generalization of dynamic effective medium approximation derived by Chylek and Srivastava, and the experimental waveguide method of determination of the effective refractive index lead to an acceptable agreement between calculated and measured values. The reduced χ2 values for these approximations ranged between 0.6 and 2.0. The remaining three approximations (volume averages of refractive indices or dielectric constants and the Maxwell Garnett relation with matrix and inclusion materials interchanged) lead to reduced χ2 values between 4.0 and 12.0 demonstrating a large disagreement between calculated and measured scattering characteristics.

Outer scale of turbulence appropriate to modeling refractive-index structure profiles.

Abstract: The outer scale of turbulence L0 has been calculated from values of the refractive-index structure coefficient CN2 obtained from spatio-angular correlation measurements of stellar scintillation. It is found that L0 ≤ 5 m for a large range of observations in France, U.S.A., and Chile and that its dependence on altitude Z follows the same general form at all these sites. The prediction of CN2(Z) profiles is shown to be feasible utilizing standard meteorological radiosonde data and this L0(Z) curve. A simple model based on dimensional analysis and a more complicated stochastic model are compared, but the latter appears to have no advantage.