Barry A. Wechsler

SPECTROSCOPIC AND PHOTOREFRACTIVE PROPERTIES OF INFRARED-SENSITIVE RHODIUM-DOPED BARIUM TITANATE

We have grown and characterized crystals of BaTiO(3) doped with Rh. These crystals have a blue-green color that is probably due to charge-transfer optical transitions involving Rh(4+) and/or Rh(3+). Electron paramagnetic resonance spectroscopy confirmed the presence of Rh(4+) centers. Self-pumped phase-conjugation measurements were performed at wavelengths between 776 and 990 nm. Reflectivities near 80% were obtained throughout this wavelength range. In addition, self-pumped phase-conjugation buildup times were measured as a function of input power at 851 nm and are significantly faster than in undoped or Co-doped crystals studied previously. BaTiO(3):Rh is therefore a promising material for near-infrared photorefractive applications.

DEPTH-RESOLVED HOLOGRAPHIC IMAGING THROUGH SCATTERING MEDIA BY PHOTOREFRACTION

A depth-resolved near-infrared imaging system has been demonstrated for recording three-dimensional images of objects embedded in diffuse media. Time-gated holographic imaging employing rhodium-doped barium titanate as the recording medium is used to acquire whole depth-resolved two-dimensional images in 1 s. Millimeter depth resolution has been achieved with a transverse resolution of ~ 30 microm.

Photorefractive properties of BaTiO 3 :Co

We measure and analyze beam-coupling gain and response time in BaTiO3 crystals doped with cobalt at levels of 50 and 100 parts in 106 for various oxidation and reduction states. We discuss the effect of cobalt doping and oxidation–reduction on the electron paramagnetic resonance and optical absorption of BaTiO3. We compare the BaTiO3:Co samples with nominally undoped and transition-metal- (chromium, manganese, iron, and iron + nickel) doped BaTiO3. We conclude that cobalt-doped BaTiO3 in the as-grown state displays high photorefractive gain that is correlated with the cobalt concentration in a reproducible manner. Cobalt appears to be the most promising transition-metal dopant for BaTiO3 investigated so far.

Photorefractive response at high modulation depths in Bi 12 TiO 20

We present data showing a nonlinear photorefractive response at high modulation depths in a Bi12TiO20 sample when applied ac fields are used. The data are interpreted by means of both a numerical finite-difference model and an analytic theory developed by Swinburne et al. [ IEEProceedings of the International Conference on Holographic Systems, Components and Applications ( Institution of Electrical Engineers, London, 1989), p. 175]. Both models provide physical insights into the performance of semiconductor and sillenite materials with ac field enhancements.

Top-seeded solution growth of BaTiO3, KNbO3, SrTiO3, Bi12TiO20 and La2-x, BaxCuO4

We present our recent top-seeded solution growth experiments of BaTiO3, KNbO3, SrTiO3, Bi12TiO20 and La2-x,BaxCuO4 single crystals.

Spectroscopic and photorefractive properties of molybdenum‐doped barium titanate

Molybdenum‐doped barium titanate crystals have been grown and characterized. Electron paramagnetic resonance spectroscopy has confirmed the presence of Mo5+ centers in reduced crystals that correlate with a strong optical absorption band at ∼600 nm. Self‐pumped phase‐conjugation and electro‐optic beam‐coupling measurements indicate that the reduced crystals are photorefractive in the visible, as well as the near‐infrared wavelength region.

Efficient self-pumped phase conjugation at near-infrared wavelengths using cobalt-doped BaTiO(3).

Using BaTiO(3) crystals doped with cobalt, we have measured the reflectivity of self-pumped phase-conjugate mirrors operating in the total-internal-reflection geometry as a function of wavelength in the range between 633 and 933 nm. We find that for cobalt concentrations above 25 parts in 10(6), the reflectivity is higher than 50% for all the investigated wavelengths. At a wavelength of 800 nm the reflectivity is independent of incident power over a range of 12 to 600 mW.

Temperature dependence of photorefractive properties of strontium‐barium niobate (Sr0.6Ba0.4Nb2O6)

Beam coupling gain and response time together with reflectivity and response time of an external ring phase‐conjugate mirror are studied as a function of temperature for a crystal of strontium‐barium niobate. The photorefractive sensitivity is increased by a factor of 5 when the crystal is heated to 65 °C. Self‐pumped reflectivities up to 19% are observed at room temperature. The reflectivity is smaller at elevated temperature.

High‐efficiency fast response in photorefractive BaTiO3 at 120 °C

Measurements of beam coupling gain and response time in BaTiO3 show a decrease by two orders of magnitude in response time and an unchanged gain coefficient as the temperature is increased from 20 to 120 °C.

Hologram fixing in Bi(12)TiO(20) using heating and an ac electric field.

We demonstrate hologram fixing in Bi(12)TiO(20) using a technique involving thermal cycling and an external ac field.