Paul T. Brown

Control of domain structures in lithium tantalate using interferometric optical patterning

Abstract We report a room temperature technique for periodically inverting the domain structure in a lithium tantalate crystal, via the simultaneous application of optical and electric fields. Ultraviolet light from an Ar ion laser was incident on a 200-μm-thick z -cut lithium tantalate crystal, illuminating the y -face which had been polished to form a biprism. The resulting interferometric pattern, formed between planar liquid electrodes applied to the + z - and − z -crystal faces, had a period of 6.3 μm. We show the results of optical control of the poling process, and discuss the theory behind light-induced ferroelectric switching.

Microstructuring of lithium niobate single crystals using pulsed UV laser modification of etching characteristics

We report a modification in the etching characteristics of lithium niobate (LiNbO3) single crystals induced by irradiating the crystal surface with pulsed UV laser light at fluences just below the ablation threshold. Modified etching behaviour has been observed using 248, 308 and 355 nm light from excimers and frequency tripled YAG lasers, for x-cut and z-cut surfaces. Both etch enhancement and etch frustration has been observed, depending on the choice of irradiation conditions. The maximum depth of surface relief structures achieved so far is >2 µm for the -z face, using etching frustration. The potential applications for microstructuring LiNbO3 using these modified etching techniques are also discussed.

Temperature sensitivity of repoling in strontium barium niobate near to the glassy transition

We report the observation of an enhanced temperature sensitivity for transient repoling near to the domain freezing temperature in ferroelectric strontium barium niobate. This work has important consequences for the use of optical fields to control domain patterns in such materials. We model the repoling characteristics of the material using a Vogel-Fulcher type response and present results showing the degree of repoling as a function of field and temperature, for short duration repoling times.

Microstructuring of ferroelectric crystal media using light poling and etching techniques

LiNbO3 and LiTaO3 are commonly used ferroelectric crystal materials. Since the first reports of successful single domain crystal growth in 1965, these materials have found increasing use in optoelectronics, laser systems, Q- switching and frequency conversion, holographic data storage, surface acoustic wave devices, integrated optics and modulator use, and most recently, microwave telecommunications. In single domain format these ferroelectrics are photorefractive, pyroelectric and piezoelectric, and possess usefully large nonlinear optical and electro-optical coefficients. If domain engineering or micron/nano-scale bulk or surface modification is performed however, greater functionality is introduced, leading to additional uses such as phase-matched frequency conversion, grating and photonic structures, and the recently proposed use in MEMS and MOEMS devices. We discuss here a range of techniques for domain engineering and domain selective etching, as well as the use of light in poling and etching modification, and illustrate this potential with several devices that we have constructed by these routes.

Anisotropic focusing characteristics of microdomain structures within crystalline Sr 0.61 Ba 0.39 Nb 2 O 6 : the crystal ball

We report the anisotropic focusing characteristics of a spherically configured region of microdomains that have been induced within a cubic-shaped crystal of Ce-doped Sr(0.61)Ba(0.39)Nb2O6. The internal spherical structure focuses extraordinary polarized light, but not ordinary polarized light. The spherical region, which is easily observed via scattering, is formed as the crystal cools after a repoling cycle through the Curie temperature, with an applied field. Analytic modeling of the thermal gradients that exist within the crystal during cooling reveals a small (<1 degrees C) temperature difference between the central and the outside regions. The similarity in shape between these temperature profiles and the observed scattering region suggests a possible mechanism for the growth of this spherical microdomained structure.

Optical control of domain structures in strontium barium niobate (SBN)

We investigate the use of combined optical and electrical techniques to control domain formation in ferroelectric SBN, and examine the periodic structures induced by spatially modulating the light intensity through the crystal during the electrical poling process. The role of photoexcited charges in compensating and stabilizing the induced domain structures is summarized, and the importance of thermal effects established. The process of domain re-ordering is shown to be particularly sensitive to temperature changes close to a domain freezing point of SBN, which occurs near room temperature. The resulting light-induced domain re- ordering is assessed using current monitoring during the repoling process, and photorefractive two-beam coupling of the resulting structures.