Gary L. Wood

Investigation of tetrabenzporphyrin by the Z-scan technique

The nonlinear transmission of tetrabenzporphyrin dissolved in tetrahydrofuran was measured with the Z-scan technique at 532 nm with nanosecond pulses. The excited-state absorption cross section, the excited-state refractive-index cross section, and the linear and nonlinear absorption contributing to a thermal index change have been determined. To our knowledge, the excited-state cross section and its effective ratio to the ground-state cross section are the largest values reported to date.

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.

Broadband photorefractive properties and self-pumped phase conjugation in Ce-SBN:60

The first use of cerium-doped Sr 0.6 Ba 0.4 Nb 2 O 6 as a broadband self-pumped phase-conjugate mirror using internal reflection is reported. The phase-conjugate reflectivity at normal incidence ranged from two percent at 442 nm to seven percent at 515 nm and was zero at 633 nm. The electron-hole competition was found to be significant and had a wavelength dependence in one sample but not the other. The charge carrier density was \sim 7 \times 10^{16} cm-3and was wavelength in-dependent. The absorption coefficient ranged from 2 cm-1at the shorter the wavelengths to zero at longer wavelengths. The dispersion in the indexes of refraction was measured and the birefringence was -0.036. The sign of the dominant charge carriers was determined to be negative and the sign of the electrooptic coefficient, r 33 , was positive. Using the above values, a wavelength dependent coupling coefficient has been determined. The experimental results indicate that the phaseconjugate reflectivity decreases at shorter wavelengths due to increased absorptive losses and experiences a threshold effect at longer wavelengths.

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.

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.

Optically induced birefringence in bacteriorhodopsin as an optical limiter

Experimental data are presented, which demonstrates an optical limiter based on a large birefringence which is optically induced in bacteriorhodopsin. The induced birefringence is observed to be a function of incident intensity, but saturates at a value of about 0.454 W/cm2. A measured value of Δn of 6.6×10−4 at a wavelength of 514 nm is reported. The observed birefringence is found to be in good agreement with a proposed model.

Fixing multiple waveguides induced by photorefractive solitons: directional couplers and beam splitters

We show how to transform multiple real-time photorefractive solitons into permanent two-dimensional single-mode waveguides impressed into the crystalline lattice of the host material. We experimentally demonstrate two specific configurations of such fixed multiple waveguides: directional couplers and multiple beam splitters.

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.