William C. Collins

Optical matrix-matrix multiplier based on outer product decomposition

An optical matrix multiplier using two linear modulating arrays in which the columns of the first matrix to be multiplied control the modulation of one array and the rows of the second matrix control the other array. Light is directed through all combinations of elements on the two arrays and the resultant beams measured by individual elements on a two-dimensional detector array. The detecting elements time integrates the intensity of light falling on each of them, which value corresponds to an element of the product of the two matrices. The invention may be implemented among other ways with two linear electrooptical arrays, a linear array of light emitting diodes and a linear electrooptical array, or two Bragg cells and a pulsed light source.

Additive and electrolytic coloration of NaF

It is shown that well‐characterized F and M centers can be introduced into NaF crystals by both additive and electrolytic coloring techniques. This success is attributed primarily to a substantial elimination of hydroxyl‐ion contamination.

Optical and thermal properties of F and F aggregate centers in KF

A detailed investigation has been carried out of the optical and thermal properties of centers such as F, FA, M and MA in pure, Na-doped and Li-doped KF. Most centers exhibit properties which are qualitatively similar to those produced in other potassium halides with the notable exception of the FA (Na) center, which has both Type I and Type II behavior.

Holographic subtraction using anisotropic centers in alkali halide crystals

Coherent partial holographic erasure and selective erasure of volume holograms is demonstrated using the linear record and erase capability of photodichroic crystals, i.e., alkali halides with anisotropic color centers.

Photodichroic materials as adaptive spatial filters in real‐time optical spectral analysis

Adaptive spatial filters based on the photodichroic property of anisotropic color centers in alkali halide crystals have been constructed for use in real‐time optical spectral analysis. Operating as change detectors in continuous spectrum surveillance, the photodichroic filter essentially sensitizes the monitoring system to detect only ’’new’’ signals. Long‐term background signals have been attenuated by factors as high as 30 000.

Improved Accuracy For An Optical Iterative Processor

A scheme is introduced and experimentally demonstrated for increasing the accuracy of an optical implementation of matrix-vector multiplication. The system is configured in a feedback loop to iteratively solve simultaneous equations. The technique is based upon a binary expansion of the matrix which is convolved with the binary expansion of the vector. This is implemented optically by the outer product synthesis of matrix products using crossed acousto-optic cells and a strobed light source.

Experimental measurements of modal transients and theoretical thermal modeling of laser diodes

Measurements of the simultaneous pulse response of the individual modes of high power laser diode arrays and broad-stripe laser diodes are presented in this paper. The modes of AlGaAs laser diodes were dispersed with an echelle grating and individually imaged onto a scanning avalanche photodiode (APD) and alternately a streak camera. Considerable power sharing over a period of 60 ns was observed among the modes of these lasers. Experimental conditions were varied and it was found that both the modulation depth and bias current had a considerable effect on the severity of the modal transients. The experimental modal transients were compared to theoretical values obtained using a finite element code to simulate temperature transients in the active area of the lasers.

Photodichroics As Active Devices For Optical Correlation

The diffraction limited resolution of photodichroic materials when used for holographic recording make them desirable candidates as spatial light modulators (SLM) in the frequency plane of the Joint Fourier Transform (JFT) correlator. Since the photodichroics generally have photosensitivities which are highly wavelength dependent, KF:LiF is a particularly good choice because its write and read sensitivities coincide with the strong 514nm and 488nm lines of the argon laser. Experimental results are reported on the use of KF:LiF as a SLM in a JFT correlator. Sections of a linear maximal length pseudo-random sequence with time-bandwidth products of up to 2.56 x 106 are successfully cross correlated.

Real-time recording medium: photodichroic KF:LiF.

Laser recording and readout measurements using the photodichroic crystal KF:LiF indicate that the material has potential as an input transducer and an adaptive spatial filter in an optical spectrum analyzer. These crystals are among the most photosensitive recording materials without gain, can be produced in large sizes at relatively low cost, and can be operated close to room temperature using thermoelectric coolers. Experiments using a high precision laser scanner providing 96.6-MHz subnsec pulses at 514 nm show that adequate recording can be accomplished with exposures less than 10 mJ/cm(2). An MTF of 40% at 72 1/mm was measured with uniform readout illumination of the recorded signal, but this is reduced if the signal is recovered by rescanning due to the convolution of the scanning beam profile with the recorded spot profile. The readout is destructive at the recording wavelength but can be read out with a much reduced decay rate by using 488 nm. The linear dynamic range in the Fourier plane was measured to be 40 dB.

Real Time Recording Medium: Photodichroic KF: LiF

Laser recording and readout measurements using the photodichroic crystal KF:LiF indicate that the material has potential as an input transducer and an adaptive spatial filter in an optical spectrum analyzer, These crystals are among the most photosensitive recording materials without gain, can be produced in large sizes at relatively low cost, and can be operated close to room temperature using thermoelectric coolers. Experiments using a high precision laser scanner providing 96.6 MHz subnanosecond pulses at 514 nm show that adequate recording can be accomplished with exposures less than 10 mJ/cm2. An MTF of 40% at 72 ℓ/mm was measured with uniform readout illumination of the recorded signal, but this is reduced if the signal is recovered by rescanning due to the convolution of the scanning beam profile with the recorded spot profile. The readout is destructive at the recording wavelength but can be readout with a much reduced decay rate by using 488 nm. The linear dynamic range in the Fourier plane was measured to be 40 dB.