Mary J. Miller

Double phase conjugation in tungsten bronze crystals

In this paper we report a new method for double phase conjugation particularly suited to the tungsten bronze crystal strontium barium niobate. It has also been observed to produce conjugate waves in BaTiO(3) and BSKNN. This new arrangement is called the bridge conjugator because the two beams enter opposing [100] crystal faces and fan together to form a bridge without reflection off a crystal face. Our measurements indicate that the bridge conjugator is competitive with previously reported double phase conjugate mirrors in reflectivity, response time, ease of alignment, and fidelity.

Strontium barium niobate as a self-pumped phase conjugator

Abstract Self-pumping has been observed in strontium barium niobate at 422 nm. An undoped crystal produced up to 60% phase conjugate reflectivity and a cerium doped crystal produced near 30%. A frequency shift in the phase conjugate wave was not observed. We also investigated asymmetrical self-defocusing and observed transmissions through the cerium doped crystal were limited to about 0.1% of the incident radiation for a wide acceptance angle.

BSKNN as a self-pumped phase conjugator

Self-pumping has been observed in a cerium-doped Ba(2-x)Sr(x)K(1-y)Na(y)Nb(5)O(15) (BSKNN) crystal at four argonion laser wavelengths. Phase-conjugate reflectivities as high as 30% were measured with response times inversely proportional to the 0.5 power of the input intensity. The response time for beam fanning in the crystal was determined to be inversely proportional to the 0.82 power of the input intensity.

Time response of a cerium-doped Sr(0.75)Ba(0.25)Nb(2)O(6) self-pumped phase-conjugate mirror.

Self-pumping in cerium-doped strontium barium niobate has been observed with phase-conjugate reflectivities near 6% and a formation time of 8 sec for a 200-mW/cm(2)beam at 442 nm. The time response for asymmetrical self-defocusing was also measured, and the observed transmissions through the crystal at normal incidence were limited to about 1.5% of the incident radiation.

Self-pumped phase conjugation in the red in photorefractive Ba 0.5 Sr 1.5 K 0.25 Na 0.75 Nb 5 O 15 and Sr 0.6 Ba 0.4 Nb 2 O 6 with cerium in 9-fold coordinated sites

Self-pumped phase conjugation has been observed at selected laser wavelengths over the range 647–780 nm. Phase-conjugate reflectivities as great as 20% were measured for power levels ranging from 2 to 100 mW. In addition, phase-conjugate and beam-fanning response times were also measured. Our observations were carried out in crystals belonging to the tungsten-bronze family; these crystals were doped with cerium at the 9-fold coordinated lattice sites to give a red photorefractive response.

Self-pumped phase conjugation with nanosecond pulses in strontium barium niobate

We report the observation of self-pumped phase conjugation by means of internal reflection in a photorefractive medium produced by a series of intense nanosecond pulses. Nanosecond pulses from a YAG laser ranging in intensity from 9 x 10(4) to 9 x 10(5) W/cm(2) were used. The crystal was rhodium-doped strontium barium niobate. The conjugate signal began with the first pulse, and the time to reach 63% of its equilibrium value scaled as I(-2). The equilibrium reflectivity was 29%. A similar cw experiment with the 514-nm line of an argon laser produced a response time that scaled as I(-1.1).

Enhanced photorefractive beam fanning due to internal and external electric fields

Significant increases (x10) in both speed and gain of the beam fanning process were obtained via three different methods in SBN and BSKNN. These methods involve the creation of a dc electric field either (1) externally, (2) by the pyroelectric effect, or (3) by thermally cycling the crystal and the presence of laser radiation. The enhanced effects were observed for both ordinary and extraordinary polarized light.

Evaluation Of Passive Optical Limiters And Switches

Optical limiters and switches can be fabricated in a variety of ways. The simplest devices are those which utilize materials that respond nonlinearly with incident intensity. We analyze and model five different passive limiter/switch concepts which could yield practical devices. These concepts include the total internal reflection, photorefractive beam-fanning, two-photon absorption, self-focusing, and self-defocusing. The analysis is carried out for typical optical materials used in the visible and infrared and the eye for a wide range of incident-pulse widths. The strength and speed of the nonlinearities required for the fundamental performance of each limiting device is provided. Factors considered in the analysis include dynamic range, transmission, response time, and the damage threshold.

Three-dimensional color holographic display

Three-dimensional (3D) color holograms are recorded in a cerium-doped, strontium barium niobate (SBN:60) photorefractive crystal. These holograms are shown to reconstruct true color reproductions of the original object with an observable field of view of 37 degrees. Angle multiplexing of two or more 3D color holograms is also demonstrated with angle tuning of the reference beam corresponding to a separation angle between stored images of 0.082 degrees. Each of these results is compared with corresponding theoretical predictions.

Color imaging in photorefractive crystals

Color phase-conjugate imaging is demonstrated using a multi-colored laser beam. Speed of response, size of the image, clarity of the image, and the intensity of the image are investigated. Color images are stored and recalled without crosstalk between different colors.