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

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

Optical data storage using orthogonal wavelength multiplexed volume holograms

We propose a volume holographic data storage scheme that employs counterpropagating reference and image beams and wavelength multiplexing for page differentation. This method is compared with that based on angular multiplexing. A reduction in holographic cross talk is predicted. Further cross-talk reduction that is due to sidelobe suppression is observed in experiments by using photorefractive crystals and the proposed orthogonal data storage

Holographic fixing, readout, and storage dynamics in photorefractive materials

Holographic gratings in photorefractive crystals that are based on charge redistribution inevitably decay as a result of ionic and electronic conduction. Under certain and restricted conditions these decay times can be acceptably long. Relevant decay rates and transient hologram field expressions are derived with special reference to LiNbO3. Some experimental data are presented

Precise control of broadband frequency chirps using optoelectronic feedback

We demonstrate the generation of wideband frequency sweeps using a semiconductor laser in an optoelectronic feedback loop. The rate and shape of the optical frequency sweep is locked to and determined by the frequency of a reference electronic signal, leading to an agile, high coherence swept-frequency source for laser ranging and 3-D imaging applications. Using a reference signal of constant frequency, a transformlimited linear sweep of 100 GHz in 1 ms is achieved, and real-time ranging with a spatial resolution of 1.5 mm is demonstrated. Further, arbitrary frequency sweeps can be achieved by tuning the frequency of the input electronic signal. Broadband quadratic and exponential optical frequency sweeps are demonstrated using this technique

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

Fixing of photorefractive volume holograms in K1-yLiyTa1-xO3

We report the f ixing of photorefractive holographic gratings with high eff iciency in a sample of K1-yLiyTa1-xNbxO3 doped with Cu, V, and Ti. Holograms are thermally fixed through the screening of a photorefractive space-charge field by a nonphotoactive species at elevated temperatures. Fixed holograms are revealed by illumination at lower temperatures. Diffraction efficiencies of 25% in a 0.54-cm-thick sample are measured. Holograms undergo thermal decay with a 0.67-eV activation energy

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)