Photorefractive gain and response time of Cr-doped strontium barium niobate

We present experimental results on the photorefractive two-beam coupling constant and response time of two Cr-doped strontium barium niobate crystals with different dopant concentrations. Both showed significantly faster response times over Ce-doped SBN:60, but with corresponding decreases in their coupling constants

Order-of-magnitude reduction of the photorefractive response time in rhodium-doped Sr0.6Ba0.4Nb2O6 with a dc electric field

We present what is to our knowledge the first report on the photorefractive properties of Rh-doped Sr0.6Ba0.4Nb2O6 and experimental results showing a reduction of the photorefractive two-beam coupling response time by more than an order of magnitude with an external dc field of 10 kV/cm

Self-starting passive phase conjugate mirror with Ce-doped strontium barium niobate

We report the use of Ce-doped SrxBa1−xNb2O6, x=0.60 and 0.75, as the holographic four-wave mixing medium in the construction of a self-starting passive phase conjugate mirror using internal reflection. Without correcting for Fresnel reflections, a steady-state phase conjugate reflectivity of 25% was measured with Sr0.75Ba0.25Nb2O6:Ce. The distortion correcting property of such a mirror was demonstrated using an imaging experiment

Photorefractive properties of Ce- and Ca-doped Sr0.6Ba0.4Nb2O6

We present the results of experimental study of the absorption coefficient, two-beam photorefractive coupling constant, and photorefractive response time of a doubly Ce- and Ca-doped Sr0.6Ba0.4Nb2O6. This crystal displays enhanced photorefractive response at near infrared wavelengths when compared to Ce-doped SBN:60. The temperature dependence of the coupling constant over the range from –30 to 40 °C has also been studied

Photorefractive Properties Of KTa_(1-x)Nb_xO_3 In The Paraelectric Phase

We report the growth of doped Potassium Tantalate Niobate (KTN) crystals, and the characterization of their photorefractive properties L. the paraelectric region. First the Top Seeded Solution Growth Method is reviewed and the growth process of a KTN:Cu,V crystal is described. Results of diffraction efficiency measurements of photorefractive gratings in these crystals at the paraelectric phase, are then presented. These experiments show high diffractio- efficiencies, and indicate the possibility of amplitude modulation of the gratings by an external field. Results showing fixation of the gratings when the sample is close to the phase transition temperature are also described

Photorefractive Properties Of KTa_(1-x)Nb_xO_3 In The Paraelectric Phase

We report the growth of doped Potassium Tantalate Niobate (KTN) crystals, and the characterization of their photorefractive properties L. the paraelectric region. First the Top Seeded Solution Growth Method is reviewed and the growth process of a KTN:Cu,V crystal is described. Results of diffraction efficiency measurements of photorefractive gratings in these crystals at the paraelectric phase, are then presented. These experiments show high diffractio- efficiencies, and indicate the possibility of amplitude modulation of the gratings by an external field. Results showing fixation of the gratings when the sample is close to the phase transition temperature are also described

Photorefractive Properties Of Cr-Doped Single Crystal Strontium Barium Niobate

Cr-doped strontium barium niobate has shown significant reduction in the time of response compared to previously grown Ce-doped crystals, with room temperature response times as short as 0.2 sec. The experimental photorefractive two-beam coupling gain and response time of 1% and 1.6% Cr-doped SBN:60 and 1% Cr-doped SBN:75 will be presented and compared to results in Ce-doped SBN:60. The photorefractive effect in Cr-doped SBN:60 has also shown a strong temperature dependence, with gain increasing by a factor of two when the crystal was cooled from 40 to -20° C. Significant gain enhancement was also predicted and obtained by applying a DC electric field of up to 10 kV/cm

Photorefractive properties of ferroelectric materials for optical phase conjugation, two-beam coupling, and holographic storage

The results of a systematic investigation of doped strontium barium niobate and potassium tantalate niobate for photorefractive beam coupling and optical holographic storage are presented in this thesis. Methods that were successfully employed to increase the magnitude of the photorefractive effect and speed up the response of these materials are also presented. Applications in the area of optical phase conjugation, distortion correction, limiting, and thresholding are also discussed. In the first part, the equations governing the photorefractive effect through band transport are introduced. The solutions giving the internal space charge field in photorefractive materials are presented for the one carrier, one species model that approximates the process in strontium barium niobate and most other materials. The coupled equations describing the two-beam coupling effect are also derived. Next, the results of experiments using as-grown potassium tantalate niobate for holographic diffraction and strontium barium niobate for two-beam coupling are presented. With KTN, the effect of Nb concentration on the phase transition, temperature dependence of diffraction efficiency and dark storage time, and the effects of the bias electric field are discussed. With SBN, the effect of dopant type, temperature dependence of the photorefractive effect, the effects of dark conductivity in Cr-doped SBN:60, and wavelength dependence are presented. The third part describes methods and results of increasing the magnitude of the photorefractive effect in SBN. Optimization of the grating period, oxidation and reduction heat treatments, temperature control, and applied fields are discussed. Significant increases in the two-beam coupling constant were observed in Cr-doped SBN:60 with applied fields of up to 10 kV/cm. An order of magnitude reduction of the response time in Rh-doped SBN:60 has been achieved with an applied field of 10 kV/cm. The final part discusses applications of these materials, particularly in the areas of phase conjugation, distortion correction, and optical signal processing. A total internal reflection phase conjugate mirror using SBN instead of BaTiO3, a one-way image transmission scheme that can send a signal through a distorting medium, thresholding using a semilinear phase conjugate mirror with grating motion, and a field controlled and enhanced optical limiter are presented