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NASA NTRS2007

Raman-Suppressing Coupling for Optical Parametric Oscillator

A Raman-scattering-suppressing input/ output coupling scheme has been devised for a whispering-gallery-mode optical resonator that is used as a four-wave-mixing device to effect an all-optical parametric oscillator. Raman scattering is undesired in such a device because (1) it is a nonlinear process that competes with the desired nonlinear four-wave conversion process involved in optical parametric oscillation and (2) as such, it reduces the power of the desired oscillation and contributes to output noise. The essence of the present input/output coupling scheme is to reduce output loading of the desired resonator modes while increasing output loading of the undesired ones.

Savchenkov, Anatoliy↗

NASA NTRS1984

Absolute two-photon excitation cross-sections in NO

A technique has been developed which allows the determination of a two-photon absorption cross-section to be made relative to the Raman scattering cross-section in nitrogen. Spatial and temporal effects associated with the lasers are ratioed out to give a result independent of laser parameters. The necessary theory to extract a cross-section from the measured ratio of a Coherent Anti-Stokes Raman Scattering (CARS) signal in N2 to a four-wave mixing signal in NO has been developed. The technique has been demonstrated on the R(22) + S(12) (J-double-prime = 9 1/2) line in NO and a cross-section of (2.9 + or - 1.8) x 10 to the -49th (cm to the 4th power)-s was determined. This technique appears to be applicable to a number of other diatomic molecules.

Burris, J.↗

NASA NTRS1984

Violation of Bell's inequalities in quantum optics

An optical field produced by intracavity four-wave mixing is shown to exhibit the following nonclassical features: photon antibunching, squeezing, and violation of Cauchy-Schwarz and Bell's inequalities. These intrinsic quantum mechanical effects are shown to be associated with the nonexistence of a positive normalizable Glauber-Sudarshan P function.

Reid, M. D.↗

NASA NTRS1985

Retrodirective-Optical-Transponder Concept

Pointing errors and optical imperfections automatically corrected. Coherent optical transponder employs nearly-degenerate four-wave mixing in nonlinear optical element to produce signal traveling back toward source of incoming signal. Return signal modulated for communication, navigation, data transmission, tracking, and identification. When perfected concept finds important civilian and military applications in line-of-sight tracking, communication and identification.

Dickinson, R. M.↗

NASA NTRS1989

Optical Processing With Photorefractive Semiconductors

Experimental phase-conjugate four-wave-mixing apparatus used to demonstrate capabilities of GaAs (and potentially of other photorefractive semiconductors like InP and CdTe) for optical processing of information. With modifications, performs any of three basic image-processing functions: transfer to different light beam, enhancement of edges, and autocorrelation. Includes crystal of GaAs of 5 by 9 by 9 mm with cubic crystalline axes. Advantages include high speed and compatibilty with other semiconductor devices.

Cheng, Li-Jen↗

NASA NTRS1988

Matrix-vector multiplication in thin photorefractive GaAs crystals

Optical matrix-vector multiplication using four-wave mixing in a thin photorefractive GaAs crystal is demonstrated. Using a thin wafer of GaAs offers the potential to integrate the encoding spatial light modulators directly on the wave-mixing medium.

Cheng, Li-Jen↗

NASA NTRS1990

Matrix.Vector Multiplication In Thin Photorefractive Crystal

Thin GaAs device integrated with other electronic and optoelectronic devices. Experiments show matrix.vector multiplication performed optically by four-wave mixing in thin crystal of GaAs. Concept applicable to thin crystals of other photorefractive materials having suitable electro-optical properties and same crystalline symmetry as that of GaAs.

Cheng, Li-Jen↗

NASA NTRS1991

Optical Computation Of Matrices From Vectors

Proposed optical apparatus generates rectangular pattern of light and dark areas, brightnesses of which represent elements of matrix product of two vectors. Photorefractive effect gives rise to four-wave mixing, which generates output beam modulated spatially by matrix product xy(SupT). Optical multipliers used as real-time analog tensor generators, components of neural networks, and generators of patterns to steer electromagnetic beams by diffraction or to effect temporary interconnections in very-large-scale integrated circuits.

Liu, Hua-Kuang↗

NASA NTRS1990

Real-time dynamic holographic image storage device

A real-time dynamic holographic image storage device uses four-wave mixing in a pair of photorefractive crystals. An oscillation is produced between the crystals which can be maintained indefinitely after the initial object beam is discontinued. The object beam produces an interference pattern in a first crystal to produce phase-conjugated object beam which is directed towards the second crystal. In the second crystal another interference pattern is created which produces a reconstructed object beam. The reconstructed object beam is directed back towards the first crystal. The interference patterns are produced by interaction of the object and phase-conjugated object beam with a read and write beam in each of the crystals. By manipulation of the ratio of the read and write beam intensities in at least one of the crystals, the phase-conjugate or reconstructed object beam output therefrom can be amplified to maintain stable oscillation between the two crystals.

Lafleur, Sharon S.↗

NASA NTRS1990

Progress of research on water vapor lidar

Research is described on several aspects of stimulated Raman scattering (SRS) of 532 nm laser light in H2, D2, and CH4. The goals of this work are to develop a more thorough understanding of nonlinear processes involving the Raman effect and four-wave mixing, and to find the best way to generate radiation at several wavelengths simultaneously, for lidar applications. Issues addressed are conversion efficiency, optimization of operating conditions (gas pressure, confocal parameter, etc.) and the distribution of output pulse energy over three Stokes components, the first anti-Stokes component, and the zeroth order (pump) wavelength. The described research and results constitute another step in the development of SRS applications for NASA's atmospheric lidar program.

Wilkerson, T. D.↗

NASA NTRS1991

Optical storage device

A new holographic image storage device which uses four-wave mixing in two photorefractive crystals is described. Photorefractive crystals promise information storage densities on the order of 10(exp 9) to 10(exp 12) bits per cubic centimeter at real-time rates. Several studies in recent years have investigated the use of photorefractive crystals for storing holographic image information. However, all of the previous studies have focused on techniques for storing information in a single crystal. The disadvantage of using a single crystal is that the read process is destructive. Researchers have developed techniques for fixing the information in a crystal so that it may be read many times. However, when fixed, the information cannot be readily erased and overwritten with new information. It two photorefractive crystals are used, holographic image information may be stored dynamically. That is, the stored image information may be read out more than once, and it may be easily erased and overwritten with new image information.

Welch, Sharon S.↗

NASA NTRS1991

Method and apparatus for second-rank tensor generation

A method and apparatus are disclosed for generation of second-rank tensors using a photorefractive crystal to perform the outer-product between two vectors via four-wave mixing, thereby taking 2n input data to a control n squared output data points. Two orthogonal amplitude modulated coherent vector beams x and y are expanded and then parallel sides of the photorefractive crystal in exact opposition. A beamsplitter is used to direct a coherent pumping beam onto the crystal at an appropriate angle so as to produce a conjugate beam that is the matrix product of the vector beam that propagates in the exact opposite direction from the pumping beam. The conjugate beam thus separated is the tensor output xy (sup T).

Liu, Hua-Kuang↗

NASA NTRS1990

Optical computing and image processing using photorefractive gallium arsenide

Recent experimental results on matrix-vector multiplication and multiple four-wave mixing using GaAs are presented. Attention is given to a simple concept of using two overlapping holograms in GaAs to do two matrix-vector multiplication processes operating in parallel with a common input vector. This concept can be used to construct high-speed, high-capacity, reconfigurable interconnection and multiplexing modules, important for optical computing and neural-network applications.

Cheng, Li-Jen↗

NASA NTRS1992

Real-time edge-enhanced optical correlator

Edge enhancement of an input image by four-wave mixing a first write beam with a second write beam in a photorefractive crystal, GaAs, was achieved for VanderLugt optical correlation with an edge enhanced reference image by optimizing the power ratio of a second write beam to the first write beam (70:1) and optimizing the power ratio of a read beam, which carries the reference image to the first write beam (100:701). Liquid crystal TV panels are employed as spatial light modulators to change the input and reference images in real time.

Liu, Tsuen-Hsi↗

NASA NTRS1991

Multiple Stokes wavelength generation in H2, D2, and CH4 for lidar aerosol measurements

Experimental results are reported of multiple Stokes generation of a frequency-doubled Nd:YAG laser in H2, D2, and CH4 in a focusing geometry. The energies at four Stokes orders were measured as functions of pump energy and gas pressure. The characteristics of the Stokes radiation generated in these gases are compared for optical production of multiple wavelengths. The competition between Raman components is analyzed in terms of cascade Raman scattering and four-wave mixing. The results indicate the possibility of using these generation processes for atmospheric aerosol measurements by means of multiwavelength lidar systems. Also, this study distinguishes between the gases, as regards the tendency to produce several wavelengths (H2,D2) versus the preference to produce mainly first Stokes radiation (CH4).

Chu, Zhiping↗

NASA NTRS1990

Real-time optical correlator using photorefractive GaAs

A real-time optical correlator based on GaAs and liquid-crystal TV (LCTV) is demonstrated. The demonstrated system has a video-frame rate limited by the speed of the LCTVs; if faster spatial-light modulators are used, the potential frame rate of a GaAs-based correlator can be as fast as 1000 frames/sec under experimental conditions. Comparisons are made between VanderLugt and joint transform and between degenerate and nondegenerate four-wave mixing. The edge-enhancement effect and the Bragg diffraction effect are discussed.

Liu, Duncan T. H.↗

NASA NTRS1992

Real-Time Optical Correlator Based On GaAs

Apparatus performs correlation between input image and reference image in real time by means of degenerate four-wave mixing in photorefractive crystal, which serves as real-time holographic medium. Gallium arsenide chosen to be photorefractive material in this application because at frame rate and level of illumination used in experiments, offers adequate diffraction efficiency. Frame rates as high as 1,000 s to negative 1st power achievable.

Liu, Tsuen-Hsi↗

NASA NTRS1993

Synthesizing Diacetylenes With Nonlinear Optical Properties

Diacetylene compounds being investigated to determine whether they have nonlinear optical properties making them useful for four-wave mixing, generation of third harmonics, phase conjugation, and like. Diacetylene monomers synthesized by sequences of chemical reactions. Monomers polymerized by ultraviolet light, forming potentially useful nonlinear optical materials.

Mcmanus, Samuel P.↗