Recording Of Dynamic Holograms Research Articles

Pulse recording of dynamic holograms in bismuth silicate crystal in a broad wavelength range

The formation of dynamic holograms in a photorefractive bismuth silicate crystal by nanosecond laser pulses with a change in the radiation wavelength is studied. An original scheme for recording holograms is proposed to preserve the grating period when operating at different wavelengths. The method of pulsed recording of dynamic gratings based on the proposed optical scheme is applied, which ensures the fulfillment of the Bragg condition for probing radiation. The originality of the scheme lies in the use of the first orders of diffraction of a transmitting diffraction grating as the reference and signal waves, as well as a telescopic system used to fix the period of the recorded grating, regardless of the wavelength used. Kinetic dependences of the diffraction efficiency of dynamic holograms in a photorefractive bismuth silicate crystal are obtained with a change in the wavelength of recording radiation in the actual spectral range (from 450 nm to 600 nm). The effect of the manifestation of competing recording mechanisms of short-lived (hundreds of microseconds) and long-lived (seconds) gratings, the contribution of which depends on the wavelength of the radiation recording the hologram, has been established. The optimal wavelength for obtaining the highest diffraction efficiency of holograms is determined. It is shown that radiation in the blue-green region of the spectrum leads to the predominant recording of a short-lived grating, while long-lived gratings dominate in the red region of the spectrum. The need to study photorefractive crystals of the sillenite family is determined by their use for multiplex recording of dynamic holograms and the implementation of the adaptive interferometry method to track changes in objects in real time.

Photoinduced Absorption and Pulsed Recording of Dynamic Holograms in Bismuth Silicate Crystals

The dynamics of photoinduced absorption and holographic-grating recording in photorefractive crystals of bismuth silicate is studied. It is shown that, with the use of nanosecond laser pulses and of the intensity on the order of 1 MW/cm2 or higher, the induced absorption due to population of the short-lived trapping levels, with characteristic relaxation times about several milliseconds or tens of milliseconds, is the case. Recording of dynamic holograms has been realized in these conditions in bismuth silicate crystals. Two mechanisms of holographic-grating recording, with the lifetimes differing by three orders of magnitude, are established. At relatively low intensities, about 1 MW/cm2 or lower, the medium response is determined by a photorefractive mechanism of nonlinearity, with relaxation times of several seconds. At the intensities exceeding 5 MW/cm2, one can observe a fast (ms relaxation times) component that may be associated with population of the short-lived traps. It is shown that the contribution of each mechanism is greatly dependent on the intensity of laser radiation and, for the intensities above 10–15 MW/cm2, the short-lived traps having millisecond lifetimes play the decisive role.

Фотоиндуцированное поглощение и импульсна запись динамических голограмм в кристаллах силиката висмута

Dynamics of the photoinduced absorption and holographic-grating recording in photorefractive bismuth silicate crystal has been studied. It has been shown that, with the use of nanosecond laser pulses and at the intensity above 1 МW/cm2, the induced absorption takes place due to population of the short-lived trapping levels having the characteristic relaxation times from milliseconds to a few tens of milliseconds. Recording of dynamic holograms in bismuth silicate has been realized in these conditions. Two mechanisms of holographic grating recording have been established, with the lifetimes differing by three orders of magnitude. Though the intensities are relatively low, below or on the order of 1 MW/cm2, the medium response is determined by a photorefractive nonlinearity mechanism with relaxation times at a level of several seconds. The intensities above 5 MW/cm2 are associated with fast components (ms relaxation times) appearing due to population of short-lived traps. It has been demonstrated that a contribution of each mechanism is dependent on the intensity of laser radiation and that, for the intensities above 10-15 MW/cm2, the decisive part is played by the short-lived traps with lifetimes on the order of milliseconds.

Liquid crystal light valve with a semiconductor substrate for dynamic holography in the infrared

Recording of dynamic holograms in the near infrared spectral range is reported for a liquid crystal light valve with a GaAs semi-insulating substrate. The interaction of weak signal and strong pump waves are studied. It is demonstrated that an out-of-phase local dynamic grating is recorded. Optimal amplitude and frequency of the applied voltage are found for maximum amplification of the weak beam. Step-like external phase modulation of the signal wave with amplitude π/2 is used to change the type of response from local to nonlocal and to achieve in such a way additional transient signal beam amplification. Study of the cells with different thicknesses of the liquid crystal layer at different grating spacings allows a seventeen-fold gain of the weak beam in the device with the thickest liquid crystal layer of 16μm at a grating period of 1000μm (the largest possible in our set-up). The amplitude of the refractive index modulation and nonlinear coupling constant n2 are estimated from the experimental results.

Dynamic Digital Holography for recording and reconstruction of 3D images using optoelectronic devices

In this work, we present the optical recording and reconstruction of dynamic 3D digital holograms using optoelectronic devices. Digital Holography technique allows recording and reconstruction of three-dimensional images of real objects, since a hologram presents both the intensity and phase information about the object. The experimental implementation of digital holographic systems for recording, as well as for numerical and optical reconstruction of three-dimensional objects became possible. We developed an experimental setup that allowed the optical recording (construction) of dynamic digital holograms (DHs) from real three-dimensional objects in CCD cameras, together with their numerical reconstruction and their optical reconstruction in a dynamic process by using a spatial light modulator, SLM; it was used a single holographic experimental setup in the entire process. We have obtained good results that enable excellent prospects for applications in recording and reconstruction of 3D scenes.

Fast novel nonlinear optical NLC system with local response

Nonlinear optical performance of a novel liquid crystalline (LC) cell has been studied in two-wave mixing experiments revealing high diffraction efficiency within extremely wide intensity range, fast recording times and spatial resolution. Photo-induced modulation of the LC order parameter resulting from trans-cis isomerisation of dye molecules causes consequent changes of refractive indices of the medium (Light-Induced Order Modification, LIOM-mechanism) and is proved to be the main mechanism of optical nonlinearity. The proposed arrangement of the electric-field-stabilised homeotropic alignment hinders the LC director reorientation, prevents appearance of surface effects and ensures the optical cell quality. The LIOM-type nonlinearity, characterised with the substantially local nonlinear optical response, could also be extended for the recording of arbitrary phase profiles as requested in several applications for light-beam manipulation, recording of dynamic volume holograms and photonic lattices.

Infrared sensitive liquid crystal light valve with semiconductor substrate.

A liquid crystal light valve (LCLV) is an optically controlled spatial light modulator that allows recording of dynamic holograms. Almost all known LCLVs operate in the visible range of the spectrum. In the present work we demonstrate a LCLV operating in the infrared. The interaction of signal and pump waves is studied for different applied voltages, grating spacings, and intensities of the recording beams. A fourfold amplification of the weak signal beam is achieved. The amplitude of the refractive index modulation Δn=0.007 and nonlinear coupling constant n₂=-1 cm²/W are estimated from the experimental results. External phase modulation of one of the recording beams is used for a further transient increase of the signal beam gain.

Full-Optical Two-Channel Adaptive System for Detecting Microcantilever Vibrations

We demonstrate a full-optical two-channel system for measuring mechanical vibrations of microoscillators, which is based on adaptive holographic interferometer using multiwave mixing in a photorefractive crystal. The orthogonal geometry of dynamic hologram recording makes possible independent operation of the measurement channels. The absolute detection limit of the system to cantilever vibrations in a channel amounted to 2.6·10−6 nm·W1/2·Hz−1/2. We tested the system in simultaneous detection of vibrations of two cantilevers with dimensions 215×40×15 μm.

Highly effective six-wave mixing in linearly absorbing organic liquids

Conditions for the realization of the highly effective transformation of a light field by dynamic holograms using a scheme of frequency-nondegenerate six-wave mixing in dyed organic liquids are determined. The mechanism of the manifestation of a nonlinear fifth-order optical susceptibility in linearly absorbing liquids is established, which is related to the nonlinearity of the thermooptical coefficient and the temperature dependence of the density and heat capacity of a solvent. The quadratic recording of dynamic holograms with a diffraction efficiency of 20% is realized in ethanol solution of copper chloride.

FREQUENCY CONVERSION OF COHERENT IMAGES ON INTRACAVITY MULTIWAVE MIXING

The schemes for recording and reading of dynamic holograms in conditions of nondegenerate four- and six-wave mixing in a nonlinear Fabry-Perot interferometer have been analyzed theoretically. It has been demonstrated that there is a possibility for a considerable improvement in the diffraction efficiency and angular selectivity of dynamic gratings in the interferometer compared to the off-cavity interaction. A method for the frequency conversion of coherent images with simultaneous phase conjugation has been realized experimentally.

Formation of the nonlinear dynamic hologram in clear organic fluids

The recording of dynamic holograms during multiwave interactions in clear organic fluids (ethanol, acetone, dioxan, etc.) is investigated. It is shown that the fifth-order nonlinearities and higher become activated along with the cubical nonlinearity under the intense laser excitation (∼100 MW cm−2) in the near-IR spectral range, which allows visualization of the IR images using different orders of diffraction.

Thermodiffusion mechanism of dynamic amplitude hologram recording in a two-component medium

An expression for the efficiency of dynamic amplitude hologram recording is obtained for a two-component medium with a concentrational nonlinearity caused by the thermodiffusion of differently absorbing particles.

Manifestation of europium ions in photoinduced absorption of lanthanum–gallium-sulfide-oxide glasses

Illumination of Eu-doped lanthanum–gallium-sulfide-oxide glasses by doubled-frequency coherent laser pulses of Nd-YAG lasers at power densities 20–120 MW/cm 2 has shown an occurrence of photoinduced changes of fundamental absorption edge. Moreover, the total absorption was changed up to 25% in the transparent spectral range. Different rare-earth impurities cause different spectral shifts of absorption edge. Among them europium ions demonstrated the highest photoinduced changes. This may be caused by a relatively large polarizabiity of these ions compared to other rare earth ions. This opens a rare possibility to use the investigated sulfide glasses for recording of dynamic holograms.

Light-induced changes in the absorption spectrum of bacteriorhodopsin under two-wavelength excitation

The results of spectrophotometric measurements of nonlinear light-induced changes in the absorption spectrum of bacteriorhodopsin D96N occurring upon simultaneous excitation at the wavelengths 633 and 441 nm in the excitation intensity range typical for recording of dynamic holograms are presented. The quantitative conditions under which the action of the radiation at one wavelength reduces the change in the optical density caused by the radiation at the other wavelength are determined.

Recording of dynamic holograms by nanosecond and picosecond laser pulses in solid-state fullerene-containing matrices

The results of a complex investigation of the recording of dynamic holograms by pulsed radiation with a duration of 20 ns and 300 ps in fullerene-containing media based on porous glasses and polymethyl methacrylate matrices are reported. Spectral analysis of these media in the range 300–700 nm was performed. The efficiency of hologram recording was found to relate with the occurrence of a band at 330 nm in the absorption spectrum of a medium. It is shown that dynamic holograms can be recorded in the fullerene-containing media by nanosecond and picosecond pulses. In the latter case, holograms arise mainly due to a change in the electronic polarizability of fullerene molecules, which is almost inertialess. The results obtained can be used in the development of ultrafast switching devices based on dynamic holograms.

Dynamic reflection holograms in CdF2 crystals with bistable centers

The diffraction efficiency and the recording and relaxation times of dynamic reflection holograms, recorded in CdF2 crystals with bistable centers are studied experimentally in the temperature range 20–100°C. In the model experiments which measured the quality of the wave reflected from the hologram, the dynamic wavefront distortions are demonstrated to be efficiently compensated using a holographic corrector based on these crystals. CdF2 crystals with bistable centers are likely to be useful in solving problems of correction of laser light wavefront and image correction in observation telescopes with nonideal primary mirrors.

Self-deflection of laser beams during holographic recording in photorefractive crystals

We have observed dynamic deflection of laser beams reflected from a crystal surface during recording of dynamic holograms in a photorefractive crystal. A theory describing the principal experimental facts is presented. The model takes into account the nonlinear interaction of space-charge waves.

Dynamic hologram recording characteristics in DuPont photopolymers

Hologram formation and diffusion reactions in photopolymer films are examined at different stages of exposure and at different spatial frequencies. Different properties of the grating formation process are evaluated from efficiency data, including the relative rates of diffusion and photoinitiated polymerization, dye absorption, and residual efficiency enhancement after UV curing. It was also found that gratings with larger periods (approximately 1.4 microm) are susceptible to erasure effects with postexposure laser illumination. In addition, crossed gratings were found to have an extended dynamic range. This effect can have a significant impact on the number of holograms formed with rotational or peristrophic multiplexing.

New mathematical model of transient two-beam energy exchange during recording of dynamic transmission holograms

A proposal is made and a justification is given of a new mathematical model of transient energy exchange between two concurrent waves in media with a local noninstantaneous nonlinear response. The relaxation time of this response is taken into account.

Influence of the purity of the starting materials on the recording of dynamic holograms in Bi12TiO20 crystals

The parameters of Bi12TiO20 crystals grown with bismuth oxide of different degrees of purity were measured by a holographic recording technique in an external ac electric field and were compared with a crystal specially doped with chromium. Various crystal parameters such as the diffusion length of the photoexcited carriers and the Debye screening length were determined. It was found that the absorption spectrum of the material and the holographic recording efficiency were strongly influenced by light chromium doping and by insufficient purity of the starting mixture.