Determination of the physical parameters controlling the photorefractive effect in KTa1-xNbx O3:Cu,V

We report photorefractive, absorption, and photoconductivity measurements made on a KTa1-xNbxO3:CuY sample after a series of reduction and oxidation treatments. All relevant physical parameters that enter into the Kukhtarev model of the photorefractive effect are determined. Photorefractive measurements are compared with those expected from theory. The oxidation-reduction process is modeled, which permits us to determine the heat treatment that is necessary to produce a given index change and response time. We discuss approaches to optimization of the photorefractive sensitivity

Characterization of a new photorefractive material: Kl-yLyT1-xNx

We report the growth and characterization of a new photorefractive material, potassium lithium tantalate niobate (KLTN). A KLTN crystal doped with copper is demonstrated to yield high diffraction efficiency of photorefractive gratings in the paraelectric phase. Voltage-controllable index gratings with n, = 8.5 x 10^-5 were achieved, which yielded diffraction efficiencies of 75% in a 2.9-mm-thick sample. In addition, diffraction was observed in the paraelectric phase without an applied field. This effect is attributed to a growth-induced strain field

Increased photorefractive sensitivity in double-doped KTa1-xNbxO3:Fe,Ti

Double-doped KTN:Fe,Ti exhibits increased photorefractive sensitivity compared with single-doped KTN:Fe and KTN:Ti. Absorption and photoconductivity measurements correlate the increase with an increased concentration of Fe in the reduced Fe2+ valence state and to an increased fraction of Fe incorporated into the crystal from the flux

Voltage-controlled photorefractive effect in paraelectric KTa1-xNbxO3:Cu,V

Experimental results that demonstrate the formation of photorefractive gratings in KTN:Cu,V in the paraelectric phase are presented. These gratings are formed using the quadratic electro-optic effect, which allows amplitude modulation of the diffracted beam by an external electric field. High diffraction efficiencies of over 50% in a 3-mm thick sample and amplitude modulation of the diffracted beam by an external field at frequencies of up to 20 kHz were observed

Subwavelength optical spatial solitons and three-dimensional localization in disordered ferroelectrics: towards metamaterials of nonlinear origin

We predict the existence of a novel class of multidimensional light localizations in out-of-equilibrium ferroelectric crystals. In two dimensions, the non-diffracting beams form at arbitrary low power level and propagate even when their width is well below the optical wavelength. In three dimensions, a novel form of subwavelength light bullets is found. The effects emerge when compositionally disordered crystals are brought to their metastable glassy state, and can have a profound impact on super-resolved imaging and ultra-dense optical storage, while resembling many features of the so-called metamaterials, as the suppression of evanescent waves.Comment: 4 pages, 3 figure

Special angle cut of potassium niobate crystal for thermal fixing

We investigated the optimal cut of potassium niobate crystals to approach the maximum exponential photorefractive gain coefficient and the highest diffraction efficiency. Volume hologram is thermally fixed in this sample and a significant enhancement of diffraction efficiency is achieved

Investigation Of The Microscopic Parameters Governing The Photorefractive Effect In KTa_(1-x)Nb_xO_3: Cu,V

We perform a microscopic analysis of the photorefractive effect in KTa_(1-x)Nb_xO_3: Cu,V. We have independently measured all relevant parameters which enter into the Kukhtarev model of the photorefractive effect. Cu is found to be the partially filled donor level responsible for the photorefractive effect. The total Cu concentration was determined from electron microprobe analysis to be 1.8(1 0^19)cm%3. A series of oxidation and reduction treatments were used to alter the concentration of Cu^(1+) and Cu^(2+). The concentration of Cu in each valence state after each heat treatment was determined using the relative magnitudes of the Cu^(1+) charge transfer band and the Cu^(2+) crystal field transition. The electron photoexcitation cross section at 514nm was determined to be 9.08(10^-20)cm^2 . The ratio of the mobility to electron recombination rate was determined from photoconductivity measurements to be 6.20(10^8) 1 /(v-cm)

Fixing of volume holograms in ferroelectric K_(1-y)Li_yTa_(1-x)Nb_xO_3

We report on the fixing of photorefractive volume holograms in potassium lithium tantalate niobate with ionic gratings and also with ferroelectric domain-reversed gratings. A diffraction efficiency of 55% is obtained with domain reversal in a 2-mm-thick ferroelectric phase K1–yLiyTa1–xNbxO3 crystal doped with Co, V, and Ti. We measured the decay rate of the domain gratings and also of the initial electron gratings and ion gratings. The domain grating decay agrees with Vogel–Fulcher fits. The activation energies for ionic and electronic conductivity are 0.76 and 0.12 eV, respectively

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