Running Hologram Research Articles

Photovoltaic effect in Bi2TeO5 photorefractive crystal

We report on the presence of a strong photovoltaic effect on nominally undoped photorefractive Bi2TeO5 crystals and estimated their Glass photovoltaic constant and photovoltaic field for λ = 532 nm illumination. We directly measured the photovoltaic-based photocurrent in this material under λ = 532 nm wavelength laser light illumination and compared its behavior with that of a well known photovoltaic Fe-doped Lithium Niobate crystal. We also show the photovoltaic current to strongly depend on the polarization direction of light. Holographic diffraction efficiency oscillation during recording and the behavior of fringe-locked running holograms in self-stabilized experiments are also demonstrated here as additional indirect proofs of the photovoltaic nature of this material.

Resonance running hologram velocity nonlinearity dependence upon light intensity in photorefractive crystals

We report on the nonlinear relation between the resonance hologram velocity and the recording light irradiance in fringe-locked running hologram experiments carried out on a nominally undoped photorefractive Bi12TiO20 crystal using 532 nm wavelength laser light. Such nonlinearity is due to the dependence of the material diffusion length on the light irradiance. Experimental data show a good agreement with the theoretical equations thus supporting the mathematical model here reported and allowing to compute the quantum efficiency for photoelectron generation, the dependence of the diffusion length upon the recorded light irradiance, and the far from saturation diffusion length.

Stabilized photorefractive running holograms, with arbitrarily selected phase shift, for material characterization

We report on the recording of stabilized running holograms in photorefractive materials with arbitrarily selected phase shift φ between the transmitted and difracted beams propagating along the same direction behind the photorefractive crystal. The dependence of the diffraction efficiency and of the hologram speed on φ, in such stabilized holograms, can be easily measured and used for material characterization. In this communication we applied for the first time this technique for studying and characterizing hole-electron competition in a nominally undoped titanosillenite crystal sample.

An improved procedure for fringe-locked photorefractive running hologram data processing

We report a new improved procedure for experimental data fitting in photorefractive fringe-locked running hologram experiments. From this fitting we compute the diffusion length LD, the Debye screening length ls, and the quantum efficiency for photo-excitation of charge carriers ?, with a lower degree of uncertainty than reported in previous publications. The procedure was successfully tried on an undoped B12TiO20 (BTO) crystal and led to LD = 0.16??m, ls = 0.038??m, and ? = 0.33, in good agreement with the already available information on this sample. The effectively applied electric field coefficient in the experiment was also estimated.

Photorefractive fringe-locked running hologram analysis in three-dimensional space

We report a new procedure allowing one to use fringe-locked running hologram experiments to characterize photorefractive materials in a very simple, reliable and direct way. This procedure is based on the representation of data in a three-dimensional space (diffraction efficiency, frequency detuning and applied electric field) that considerably facilitates data fitting. The latter procedure is evaluated by means of a mathematical simulation. The technique is applied to a photorefractive Bi12TiO20 crystal sample in order to verify its adequacy for computing some of the more relevant material parameters: diffusion length, Debye screening length and quantum efficiency for photoelectron generation. The effectively applied electric field inside the sample is obtained at the same time. The results are in good agreement with data already available for this sample.

Feedback operation for fringe-locked photorefractive running hologram

We report an analysis of the feedback circuit operation that produces fringe-locked photorefractive running holograms. In agreement with theoretical expectations we experimentally demonstrate that the speed of this running hologram depends on material and experimental parameters and is not sensibly affected by the settings in the feedback loop, a fundamental feature of this technique. We also show that fringe-locked experiments produce much less dispersive data than those obtained from plain running hologram.

Speed and diffraction efficiency in feedback-controlled running holograms for photorefractive crystal characterization

We report the measurement of the diffusion length, the Debye screening length and the quantum efficiency of photoelectron generation in strongly light absorbing photorefractive Bi12TiO20 crystals, using fringe-locked running hologram experiments. The effective applied electric field inside the sample is also computed and self-diffraction is considered. The novelty here, as compared to formerly reported experiments, is that the diffraction efficiency is now measured simultaneously with the hologram speed v. From these data the above referred to photorefractive and experimental parameters are obtained without the need for additional experiments. The method is used to analyze two photorefractive Bi12TiO20 crystal samples, in different experimental conditions, using the 514.5 nm wavelength. The computed parameters are in good agreement with the available information about these samples.

Photorefractive running hologram for materials characterization

We report a theoretical model for a photorefractive running hologram in bulk-absorbing materials in the presence of self-diffraction and use this model to analyze experiments for photorefractive materials characterization. A nonperturbative technique that allows one to measure at the same time the diffraction efficiency and the output beam’s phase shift is reported, and its advantages are discussed. We use this technique and apply the theoretical model to compute some parameters for the electron-charge carriers (Debye screening length ls≈0.03 µm, diffusion length LD≈0.14 µm, and photoexcitation quantum efficiency Φ≈0.45) at the 514.5-nm-wavelength laser line for a nominally undoped Bi12TiO20 crystal. Particular experimental features are detected and assumed to be consequences of hole–electron competition in this sample.

Feedback-controlled running holograms in strongly absorbing photorefractive materials

We propose a mathematical model for the movement in absorbing materials of photorefractive holograms under feedback constraints. We use this model to analyze the speed of a fringe-locked running hologram in photorefractive sillenite crystals that usually exhibit a strong absorption effect. Fringe-locked experiments permit us to compute the quantum efficiency for the photogeneration of charge carriers in photorefractive crystals if the effect of bulk absorption and the effective value of the externally applied field are adequately taken into consideration. A Bi12TiO20 sample was measured with the 532-nm laser wavelength, and a quantum efficiency of Φ=0.37 was obtained. Disregarding absorption leads to large errors in Φ.

Phase-controlled photorefractive running holograms

We report on the use of phase modulation in two-wave mixing with negative feedback to record stabilized photorefractive running holograms with arbitrarily fixed phase shift between the transmitted and the diffracted beams behind the crystal. By adequately choosing this phase one can select the running hologram speed and associated properties like diffraction efficiency. This technique is an alternative to the classical frequency detuning one with the advantage that the recording is at the same time actively stabilized referring to the own hologram being recorded. We describe the setup, analyse its behavior and report experimental results for a Bi 12TiO 20 crystal.

Adaptive fringe-locked running hologram in photorefractive crystals: errata

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Jaime Frejlich, Paulo Magno Garcia, and Lucila Cescato, "Adaptive fringe-locked running hologram in photorefractive crystals: errata," Opt. Lett. 15, 1247-1247 (1990) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Fringe-locked running hologram and multiple photoactive species in Bi12TiO20

Fringe-locking techniques ar used for the recording of stable 90 ° phase-shifted running holograms in photorefractive crystals. The use of this technique permits the characterization of a fast and a slow photoactive species in Bi12TiO20. We compare our results with those obtained from other methods and discuss the practical interest of this technique.

Adaptive fringe-locked running hologram in photorefractive crystals

We have recorded running holograms in a photorefractive crystal with an applied electric field, using a 90 degrees phase-shift fringe-locked interference pattern of light. This method provides a simple way to obtain optimal conditions for nonstationary holographic recording. The experiment that we describe allows us to calculate the crystal diffusion length L(D) and provides direct evidence of the occurrence of running holograms in photorefractive crystals. Experimental results for a Bi(12)SiO(20) sample are reported.