Edward J. Sharp

Dimensionality and size of photorefractive spatial solitons.

We study experimentally self-trapping of optical beams in photorefractive media and show that the trapping is inherently asymmetric with respect to the two (transverse) trapping dimensions. We also present experimental results that show how the sizes of the resultant photorefractive spatial solitons are independent (within their range of existence) of the amplitude of the externally applied electric field used to generate them.

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.

Stability of photorefractive spatial solitons.

We present a theoretical analysis of the stability of photorefractive spatial solitons along with experimental results that show that the solitons are stable for small-scale perturbations but break down when the perturbations exhibit a transverse scale comparable with the soliton size (cross section).

Growth and optical properties of ferroelectric tungsten bronze crystals

Abstract The state of the art in the Czochralski growth of various optical-quality ferroelectric tungsten bronze single crystals is reviewed with respect to crystal structure, phase transitions and cationic make-up. Based on our growth of over 25 single crystal bronzes, we have classified these bronzes into four categories having distinctly different ferroelectric and optical characteristics. With the use of this classification, optimal bronzes can be chosen for specific electro-optic and photorefractive applications.

Tunable quasi‐phase matching using dynamic ferroelectric domain gratings induced by photorefractive space‐charge fields

We demonstrate a method of dynamic, tunable quasi‐phase matched second‐harmonic generation using optically induced polarization gratings with periods equal to twice the coherence length. These gratings increase the peak second‐harmonic conversion efficiency by a factor of 17 above a poled strontium barium niobate crystal, to 0.01% for fundamental beam intensities of 0.8 MW cm−2. We generate quasi‐phase matching spectral response peaks as narrow as 0.175 nm and tailor the response by writing an ensemble of gratings in the same volume, each of which enhances the second‐harmonic generation at a predetermined wavelength.

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).