Enhanced responsivity of non-steady-state photoinduced electromotive force sensors using asymmetric interdigitated contacts.

The responsivity at a constant detection area of non-steady-state photoinduced electromotive force (photo-emf) detectors is improved by a factor equal to the number of contact pairs contained in asymmetric interdigitated surface contacts. The polar nature of photo-emf current generation requires contact asymmetry in which one increases the total signal by blocking the illumination between alternate contact pairs, in distinct contrast to the behavior of conventional interdigitated contacts fabricated upon isotropic photoconductors.

Single-pixel demonstration of innovative adaptive optics by use of a charge-transfer membrane light modulator.

We have constructed and demonstrated a single-pixel implementation of an all-optical membrane-based spatial light modulator as a compact optical wave-front error correction device. High rates of response of as much as 20 kHz in an open-loop configuration were obtained. The device was then used in an adaptive-optics servo to compensate successfully for a 1-kHz sinusoidal phase error with a peak-to-peak excursion of approximately pi/7 rad. A small-signal servo gain of the order of 10 was inferred from the closed-loop measurements.

Optical real-time defect-enhancement diagnostic system.

We have demonstrated an all-optical diagnostic system that enhances the observation of defects in periodic structures. This real-time technique employs a spatial light modulator as a smart-pixel array for information processing in the Fourier transform plane of a lens. The system also includes a phase-conjugate mirror for autoalignment and for correction of optical wave-front aberrations that are imparted on the object light by the smart-pixel processor and its associated optical train.

Retromodulation/conjugation using a self-pumped atomic sodium phase-conjugate mirror.

A self-pumped atomic sodium phase-conjugate mirror was modified to include an amplitude modulator, which thus formed a device capable of encoding temporal information onto the phase-conjugate return beam. Modulation rates of as much as 4 MHz with modulation depths in the range of 70-90% (both limited by the electronics and the modulator) have been obtained by using an intracavity acousto-optic modulator.

Spatial convolution and correlation of optical fields via degenerate four-wave mixing.

A nonlinear optical technique is described that performs, essentially instantaneously, the functions of spatial correlation and convolution of spatially encoded waves. These real-time operations are accomplished by mixing spatially dependent optical fields in the Fourier-transform plane of a lens system. The use of a degenerate four-wave mixing scheme eliminates (in the Fresnel approximation) phase-matching restrictions and (optical) frequency-scaling factors. Spatial bandwidth-gain considerations and numerical examples, as well as applications to nonlinear microscopy, are presented.

Narrow optical bandpass filter via nearly degenerate four-wave mixing.

It is shown that a nearly degenerate four-wave mixing process is capable of yielding a real-time optical bandpass filter. The filter has a large field of view and is capable of providing an amplified bandpass. Moreover, the conjugate nature of the output field can be utilized to increase the signal-to-noise ratio of the device. For a 1-cm interaction length in a nondispersive medium, the optical bandpass at 5000 A can be varied from ~9 GHz down to the linewidth of the exciting laser.