Diffractive optic sensor for remote-point detection of ammonia.

Remote-point photonic sensors are fabricated and evaluated. They are based on nanocomposite thin films comprising NiCl(2) nanocrystals embedded in sol-gel silica matrix and are patterned using direct UV laser microetching techniques to form surface relief structures, which exhibit environment sensitive optical diffraction effects. A strong response to ammonia is detected via the alteration of diffraction efficiency of its orders upon exposure to the analyte. Detection of ammonia in the 2 ppm level with a typical response time of about 30 s in the ambient, 50% RH 20 degrees C, room environment is demonstrated.

Etching and printing of diffractive optical microstructures by a femtosecond excimer laser.

Diffractive optics fabrication is performed by two complementary processing methods that rely on the photoablation of materials by ultrashort UV laser pulses. The spatially selective ablation of materials permits the direct microetching of high-quality surface-relief patterns. In addition, the direct, spatially selective transfer of the ablated material onto planar and nonplanar receiving substrates provides a complementary microprinting operation. The radiation from the ultrashort pulsed excimer laser results in superior quality at relatively low-energy density levels, owing to the short absorption length and minimal thermal-diffusion effects. Computer-generated holographic structures are produced by both modes of operation. Submicrometer features, including Bragg-type structures, are microprinted onto planar and high-curvature optical-fiber surfaces, demonstrating the unique ability of the schemes for complex microstructure and potentially nanostructure development.

Photosensitivity of lead germanate glass waveguides grown by pulsed laser deposition.

We report very large photoinduced refractive-index changes Dn, of the order of ~10(2), in lead germanate glass waveguides grown by pulsed-laser deposition. The magnitude of Dn was derived from measurements of diffraction efficiency for gratings written by exposure to 244-nm light through a phase mask, whereas the sign of Dn was determined from ellipsometric data. Results are shown for films grown under oxygen pressures ranging from 1 chi 10(-2) to 6 chi 10(-2)mbars (1.33mbars=1 Torr).

Ti:sapphire planar waveguide laser grown by pulsed laser deposition.

We document the lasing performance of a waveguiding layer of Ti:sapphire, of ~12-mum thickness, grown by pulsed laser deposition from a 0.12-wt.% Ti(2)O(3) Ti:sapphire single-crystal target onto an undoped z-cut sapphire substrate. Lasing around 800 nm is observed when the waveguide layer is pumped by an argon-ion laser running on all-blue-green lines, with an absorbed power threshold of 0.56 W, with high-reflectivity (R>98%) mirrors. With a 5% pump duty cycle and a T=35% output coupler, a slope efficiency of 26% with respect to absorbed power is obtained, giving quasi-cw output powers in excess of 350 mW.

Excimer laser use for microetching computer-generated holographic structures.

Excimer-laser microetching of a variety of materials is applied to the fabrication of surface-relief optical microstructures of arbitrary morphology, with particular emphasis on computer-generated holographic structures. High-definition, high-radiation-intensity selective laser ablative etching in conjunction with step-and-repeat (period) replication or raster (pixel) scanning is used. To support such developments, the characteristic etching properties of a wide range of solid materials, from metals to semiconductors and polymers, are studied. Optical-interconnect and generic object holograms are produced by means of this alternative one-step holographic information-recording method.

Photorefractive adaptive transmission system.

A photorefractive system based on the combined operation of a strontium barium niobate input amplifier and a self-pumped barium titanate phase-conjugator crystal is presented and analyzed. Amplified real-time phase-conjugate wave-front generation in this system is demonstrated. The system's ability to all-optically, temporally modulate a weak probe signal and to transmit it back to its source by means of amplified dynamic phase conjugation demonstrates its potential in adaptive optical transmission schemes.

High-fidelity image amplification and phase conjugation in photorefractive Bi(12)SiO(20) crystals.

Wide-angle, large space-bandwidth-product coherent image amplification with a flat spatial frequency response is demonstrated in photorefractive Bi(12)SiO(20) crystals under nonstationary grating recording conditions. By utilizing large-divergence, mutually phase-conjugate pump beams provided by a self-pumped BaTiO(3) crystal, high-fidelity phase conjugation with high reflectivity in Bi(12)SiO(20) is demonstrated.

Real-time optical Wiener-Kolmogorov and novelty filtering with phase conjugation.

Real-time all-optical Wiener-Kolmogorov filtering is demonstrated by using two coupled photorefractive phase-conjugate mirrors. A novelty filtering system based on the combination of the present operation and the operation of real-time image subtraction previously presented [Opt. Lett. 13, 503 (1988)] is outlined. By comparing an input signal pattern with a set of known stored patterns, all known information in the input would be eliminated from the output, while any novel information would appear. This latter scheme could also be used in image-synthesis applications.

Multiplexed permanent and real time holographic recording in photorefractive BSO.

We report permanent hologram recording in crystals of photorefractive bismuth silicon oxide using reversible photochromic effects. At a recording wavelength of 488 nm, exposures of several minutes produce areas of faint discoloration in which the permanent hologram is stored. The normal photorefractive behavior is unaffected, however, permitting spatial multiplexing of both real time and permanent holograms. Experimental results and characteristics of this permanent recording in combination with the photorefractive process are presented.

Applications of Multiplexed real time permanent holographic recording in photorefractive BSO.

Photochromic effects in crystals of photorefractive bismuth silicon oxide have been used for the recording of permanent holograms. The combination of this permanent recording with the usual photorefractive real time recording has revealed some novel techniques in information processing and interferometry. These are based on the possibilities of multiplexing two distinct holographic gratings having identical grating wave vectors within the same crystal volume. Techniques ranging from image synthesis and logic operations to holographic interferometry and all-optical switching are demonstrated.

Real-time parallel optical logic in photorefractive bismuth silicon oxide.

Fast parallel analog and digital optical computing operations are demonstrated by using an interferometric arrangement with photorefractive bismuth silicon oxide. Image subtraction, coherent weighted-image addition, exclusive OR/NOT, and OR optical gates are achieved by controlling the relative phase shifts of two phase-conjugate waves generated by degenerate four-wave mixing.