Jacques E. Ludman

Holographic solar concentrator

A solar concentrator receives sunlight for generating solar power with the concentrator including holographic optical element (HOE) separators for separating sunlight into separated bands, including HOE concentrators for concentrating the separated bands into concentrated bands, including HOE reflectors for reflecting the concentrated bands as reflected bands onto a multiple junction photovoltaic solar cell for generating the solar power with reduced aberrations of the bands for improved conversion of the solar light into the generator solar power, all of which can be constructed in an integrated structure using spacers, waveguides, and a substrate, where the HOEs use chirp Bragg gratings for reducing optical aberrations of the separated, concentrated, and reflected optical bands, with the option of multiple HOE separators for receiving sunlight from various angles of incidence.The design of a holographic solar concentrator that considers problems inherent in concentration is presented. (AIP)

Very thick holographic nonspatial filtering of laser beams

Philip Hemmer, MEMBER SPIE Rome Laboratory RL/EROP, 63 Scott Road Hanscom Air Force Base, Massachusetts 01731 Abstract. A novel device, the nonspatial filter, is described for laser beam cleanup. It is based on the Bragg selectivity of thick holograms. Unlike pinhole and fiber spatial filters, which employ lenses and apertures in the transform plane, nonspatial filters operate directly on the laser beam. This eliminates the need for laser beam focusing, which is the source of many of the material and alignment instabilities and laser power limitations of spatial filters. Standard holographic materials are not suitable for this application because differential shrinkage during processing limits the maximum Bragg angle selectivity attainable, and because they are generally too thin. New technologies that eliminate the problem of differential shrinkage are described. These technologies are based either on the use of a rigid porous substrate material, such as porous glass, filled with a light-sensitive material, such as holographic photopolymers or dichromated gelatin, or on the use of a thick photopolymer with diffusion amplification (PDA). We report results of holographic nonspatial filtering of a laser beam in one dimension, with an angular selectivity of better than 1 mrad.

Microcomputer-based programmable optical correlator for automatic pattern recognition and identification

A microcomputer-based programmable optical correlator (MPOC) is proposed for automatic pattern recognition and identification. A programmable magneto-optic spatial light modulator and a liquid-crystal light value are used to perform a real-time joint-transform correlation operation. Since the proposed MPOC consists of a microcomputer and an optical processing system, it has the advantage of real-time programmable processing capability for large space-bandwidth-product information. The basic theory and a feasibility study of the technique are given.

Bimodal optical computers.

Analog optical solutions of numerical problems tend to be fast, simple, and inaccurate. Digital optical or electronic solutions to the same problems tend to be slower, harder, and more accurate. In circumstances outlined here, hybrid analog-digital systems can be built which give the accuracy of digital solutions with intermediate degrees of speed and simplicity. Because at any instant these processors are working in either the analog or the digital mode, we call them bimodal optical computers.

The optimization of a holographic system for solar power generation

Abstract A holographic device has been developed that greatly improves the efficiency of solar energy conversion. The single-element hologram focuses light, spectrally splits it and diverts unwanted infrared heat away from the solar cells. The output appears as a thin concentrated line, focused perpendicular to the hologram and displaced to the side. Solar cells are placed along this line such that each cell absorbs only the wavelengths which it can efficiently convert to electric power. The theoretical and experimental development of this system are discussed, as well as its application in space and on Earth. The system is excellent for space applications since the holograms are single element, very lightweight, and require minimal cooling. For terrestrial purposes, the projected costs of the system are nearly a factor of two lower per kWh than other solar concentrator systems; thus it is competitive with conventional power generation systems. Other state of the art holographic solar power generation systems are also discussed.

Real-time joint spectral-spatial matched filtering

Abstract A technique for real-time joint spectral-spatial matched filtering is presented. The technique involves the real-time conversion of an input color image into a set of sampled monochromatic coherent images through the use of a tricolor grid and real-time spatial light modulator. These color-coded monochromatic images are then processed by a multi-channel, coherent matched filtering subsystem. The advantage of this technique over prior matched filtering methods is its ability to use both color and shape in recognizing objects.

Single holographic element wavelength demultiplexer

A simple single-element holographic optical demultiplexer for wavelength division multiplexing in optical fiber systems is described. The single holographic element performs all the required functions of collection, separation, and focusing. Experimental results for a device operating in the visible region of the spectrum are described. The device is bidirectional and also functions as an efficient multiplexer.

Holography for the new millennium

I. Overview: Where Holography is Going.- II. Display Holography: 1. Color Holograms. 2. Real-Time Autostereographic Three-Dimensional Displays.- III. Special Modalities and Methods: 1. Edge-Lit Holograms. 2. Subwavelength Diffractive Optical Elements. 3. Coherence Gated Holograms. 4. Sculpturing of Three-Dimensional Light Fields by Iterative Optimization.- IV. Applications: 1. Solar Holography. 2. Holographic Optical Memories. 3. Holography and Speckle Techniques Applied to Nondestructive Measurement and Testing. 4. Diffuser Display Screen. 5. Holographic Nonspatial Filtering for Laser Beams. 6. Particle Holograms. 7. Holographic Antireflection Coatings.- V. Physics and Holography: 1. Holography and Relativity. 2. Quantum Holograms.

Photovoltaic Systems Based on Spectrally Selective Holographic Concentrators

A holographic device has been developed that greatly improves the efficiency of solar energy conversion. The single-element hologram focuses light to the side and also spectrally splits it. The output appears as a thin concentrated line, focused perpendicular to the hologram and displaced to the side. Different wavelengths are diffracted, concentrated, and dispersed to different locations on the line which resembles an elegant rainbow in the visible. The hologram lets each of two or more different solar cells absorb only those wavelengths which can efficiently convert to electric power. The device also prevents overheating by diffracting unwanted infrared radiation away from the cells. The side focus eliminates shadow effects, and cooling is easy, since the cells are not cascaded and the heat load is minimal. This novel system is ideal for concentrated, split-spectrum, high efficiency solar power generation.

Color object identification by monochromatic binary correlation

A real-time polychromatic image correlator that uses a magnetooptic (MO) spatial light modulator (SLM) device for pattern recognition based on both the color and shape of an input object is presented. The proposed system utilizes a multichannel spectral matched spatial filter employed in a binary coherent optical correlator. Input color images are transformed into binary color coded coherent images by a color grating. The color encoded images are read out by a charge coupled device interfaced with a MO SLM. The color encoded binary images are then processed by a multichannel joint spectral matched spatial filter synthesized by monochromatic light. Pattern recognition experiments for naturally illuminated real color objects are presented.