Kinetics Of Diffraction Efficiency Research Articles

Polarization holographic gratings in PAZO polymer films doped with particles of biometals

The paper presents a study of the diffraction efficiency of polarization holographic gratings recorded in thin films of the azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]) doped with Cu(II) 3-amino-5,5′-dimethylhydantoin (CLP) and Ni(II) 3-amino-5,5′-dimethylhydantoin (NLP) at three different concentrations, namely 1, 2 and 5 wt.%. The influence of the dopants composition and concentration on the parameters of the polarization holographic gratings recorded in the thin composite films has been discussed. The gratings are recorded with a He-Cd gas laser with wavelength 442 nm. The polarization of the recording beams was left and right circular and the recording angle was 20°. Along with the anisotropic grating in the volume of the media, surface relief is also formed. The diffraction efficiency kinetics is probed at 635 nm and the height of the relief gratings is determined by AFM. Diffraction efficiency (η) higher than 30 % was achieved for the hybrid samples, as well as 585 nm surface relief height.

Polarization holographic gratings with enhanced parameters recorded in azopolymer based nanocomposite materials

We present study of the parameters of polarization holographic gratings recorded in thin films of the azopolymer PAZO (Poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]) and in a composite PAZO-based organic/inorganic material with incorporated TiO2 nanoparticles with size 21 nm and different concentrations. The gratings are inscribed by two plane waves with left and right circular polarization from a He-Cd gas laser (442 nm) at recording angle 20°. Along with the anisotropic grating in the volume of the media, surface relief is also formed. Gratings with different spatial frequencies are obtained by varying the recording angle. The diffraction efficiency kinetics is probed at 635 nm and the height of the relief gratings is determined by AFM. Our results indicate that the diffraction efficiency for the hybrid samples is enhanced with respect to the pure azopolymer films. Comparison is also made between polarization response of samples deposited from water and from methanol solution.

Dynamics of Diffraction Efficiency of Superimposed Volume Reflection Holograms at Their Simultaneous Recording in Photopolymer Material

The new experimental data on the dynamics of diffraction efficiency (DE) of superimposed volume reflection holograms with a grating period of $${\sim}$$ 250 nm is obtained at their simultaneous recording in the photopolymer material BAYFOL HX TP. The character and parameters of their interaction are established when exposure of one hologram is delayed relative to the other one. It is revealed that the DE dynamics is practically not affected by variations in diffusion time of monomer in the range $$0.12<t_{D}<0.17$$ s, but the transient behavior of the photopolymerization parameter $$\tau_{p}$$ , which increased in our experiments from 5 to 15 s, becomes considerably visible. The well-known equations of the photoinduced variation in the photopolymer refraction index are improved with account for the character of variation in the parameter $$\tau_{p}$$ . The calculated dependences of DE dynamics obtained with refined formulas are in good agreement with experimental data (mean square deviation is $${\sim}2\%$$ ).

Polarization holography for direct surface grating patterning on chalcogenide nanomultilayers

In present work the one-step direct relief formation of diffraction gratings using As2S3–Se nanomultilayers were studied. We have carried out a study of the polarization sensitive recording properties of the chalcogenide glasses in form of nanomultilayers. Nanomultilayers deposition, samples structure and recording process peculiarities were discussed. The surface relief gratings were patterned into nanomultilayers by method of polarization holography. It was shown that surface relief vector holographic gratings formed by two ±45°polarization states and by left-right circular polarizations are phase gratings. The kinetics of diffraction efficiency of both phase and intensity gratings were compared. The possible explanations based on dielectrophoretic forces existing in fluidic systems or H. Fritzche’ model supposing the presence of minimum isotropic volume with the anisotropic structural units are discussed. The method offers the advantage of the fabrication of relief structures with one-step processing, without the necessity for any subsequent processing steps.

Polarization holographic gratings with high diffraction efficiency recorded in azopolymer PAZO

Azopolymers are one of the most efficient materials able to record the polarization state of light. They have numerous applications, such as data storage and diffractive optical elements with unique polarization properties. An essential parameter for each diffractive element is its diffraction efficiency η. In order to optimize the recording conditions and obtain high-efficient polarization holographic gratings, in the present work we study the dependence of the diffraction efficiency on the recording angle and thickness of a series of azopolymer layers. Three recording angles are used − 10°, 20° and 30° and three series of thin films with thicknesses 470, 850 and 2400 nm from the water-soluble azopolymer PAZO. The gratings are inscribed by two plain waves with left and right circular polarization from a He-Cd gas laser (442 nm). The diffraction efficiency of the gratings is probed with a right hand circularly polarized beam from a probe laser with wavelength 635 nm. The kinetics of diffraction efficiency η(t) in the + 1 diffraction order are presented and compared. Our experimental results indicate that highest diffraction efficiency (more than 40%) is obtained for the sample with thickness 2400 nm and for recording angle 10°. As the holographic recording in azopolymers is usually accompanied by formation of surface relief gratings, the surface topography of the recorded samples is also investigated by atomic force microscopy.

Dynamics recording of holographic gratings in a photochromic crystal of calcium fluoride

Dynamics of diffraction efficiency was monitored during recording a holographic grating in additively coloured CaF2 photochromic crystal at 180-200°C. Reciprocity failure revealed in the study was attributed to diffusion playing the crucial role in grating formation: recording at larger laser power goes faster but requires more energy. The efficiency of a recorded hologram is found to depend on the temperature; maximum diffraction is measured at the temperature far below that of recording, supposedly because of dramatic distortions suffered by the crystal along with exposure.

Some features of information properties of holographic recording media based on a photoconducting carbazolyl-containing oligomer doped with an organic electron acceptor.

Unusual multimodal kinetics of diffraction efficiency in the cycle of hologram recording and erasing were observed in the recording media for the holographic photothermoplastic technique. It was shown that this effect is caused by competition between the simultaneous development of regular and random "frosty" surface reliefs of the photoconducting polymer film during the hologram development. The mechanism explaining the decrease of the maximal diffraction efficiency as compared to its calculated value is discussed.

Fast Response Beam Coupling in Dye Doped Liquid Crystal Cells Sandwiched with ZnSe Coated Substrates

ABSTRACTIn this paper we present fast response processes in dye doped liquid crystal cell with ZnSe layers on electrodes. Two-wave mixing and grating monitoring experiments were performed to characterize this liquid crystal system. With the help of photoconductive layers, the response time was reduced to a few milliseconds, which improved further the response rate in liquid crystal photorefractive system. A peak in response time versus applied voltage and unexpected oscillations in diffraction efficiency dynamics were observed, which implies unconventionally complex charge dynamics associated with SPPs excited at one of the photoconductive layer/liquid crystal interfaces.

Polarization volume holograms in layers of polymethylmethacrylate with phenanthrenequinone

Polarization volume holograms are recorded in the polymethylmethacrylate layers that contain phenanthrenequinone at a molar content of 2.5–3%. The effect of the polarization of recording beams on the kinetics of diffraction efficiency and properties of holograms is analyzed. Polarization hologram recording in the polymethylmethacrylate layers with phenanthrenequinone and a relatively high optical stability of the holograms are demonstrated.

Paper No P27: Features of Polarization Diffraction Gratings Switching Under the Influence of Bipolar Electric Pulses

AbstractThe diffraction efficiency dynamics of planar‐planar periodic liquid crystal structure under the influence of quasistatic (1 kHz), as well as pulse electric fields is studied. In quasistatic control mode ±1 diffraction orders are observed in the voltage absence, and at the electric field switching on the diffraction disappears, that is, only zero order is observed. In contrast to the quasistatic control mode, under the influence of single bipolar electric pulses the increase in diffraction efficiency is observed in ±1 order, and at that the zero order is absent. The dependence of diffraction efficiency on the control pulses repetition frequency and amplitude is also studied. The results of these investigations can find application in displays development.

Kinetics of polarization gratings assisted with polarized violet light in bacteriorhodopsin films

Polarization gratings can be recorded in bacteriorhodopsin films by an orthogonal pair of linearly or circularly polarized beams. If a linearly polarized auxiliary violet light is added during the grating formation, the grating becomes polarization-sensitive. A theoretical model based on the two-state photochromic theory is proposed to calculate the diffraction efficiency kinetics of these polarization gratings. In both cases, the additional linearly polarized auxiliary violet irradiation improves the steady-state diffraction efficiency and leads to a cosine modulation of the steady-state diffraction efficiency by the polarization orientation of the readout beam. Experiment results demonstrate the correctness of the theoretical model.

Pattern of liquid crystalline droplets induced by two beam interference in azobenzene derivative

A pattern of liquid crystalline droplets dispersed in the isotropic liquid can be formed during illumination by two interfering laser beams in certain range of the temperature and the light intensity. Azobenzene derivative substituted by long alkyl and alkoxy chains exhibiting smectic phases has been used for the study. The pattern can be reversibly erased and rewritten by shutting down and opening of the interfering beams. Polarized microscope images have shown the formation of numerous liquid crystalline droplets at bright regions of the interference fringes. Influence of the temperature and the light intensity has been studied by measuring the diffraction efficiency dynamics. Photothermal and photoorientational mechanisms of the formation of liquid crystalline droplets pattern have been proposed and discussed.

Light-stimulated growth of isotropic domains in nematic liquid crystal

Growth dynamics of single isotropic domains, appearing in liquid crystalline azobenzene derivative during diffraction grating recording has been studied under the polarized microscope. Theoretical approach considering light stimulation as main reason of the growth has been proposed. Growth dynamics of population of the domains has been studied by fitting diffraction efficiency dynamics, using diffraction on rectangular phase grating model. Influence of parameters concerning: material properties, domain growth function and incubation time distribution have been studied by series of simulations. Proposed model explains the local extrema effect on diffraction efficiency curves and can be used for fitting with very good precision.

On the long time holographic grating recording process in azo-polymer

The authors report on a complex diffraction efficiency dynamics of the holographic grating recording process in azobenzene-functionalized polymer for a long recording time. The nonexponential dynamics was explain by the mechanism which assumes (i) simultaneous formation of three coupling phase gratings with constant, equal 0 or π, phase shifts between them and (ii) occurrence of gratings erasure processes when the recording time is long. Based on these assumptions and applying the Bessel function, the diffraction efficiency dynamics was calculated.

Synthesis, Characterization, and Study of Photoinduced Optical Anisotropy in Polyimides Containing Side Azobenzene Units

In this paper, novel processable aromatic polymers with imide rings and attached as side-chain azobenzene units are presented. Polymers differ in the chemical structures of chromophores and polymer backbones. Azopolymers were obtained by a two-step synthetic approach. This includes the preparation of a precursor poly(esterimide) and poly(etherimide) with pendant phenolic hydroxyl groups, followed by the covalent bonding of NLO chromophores onto the polyimide backbone by the Mitsunobu reaction. The degree of functionalization of polymers was estimated by UV-vis spectroscopy. Polymers were characterized and evaluated by FT-IR, (1)H NMR, X-ray, UV-vis, DSC, and TGA methods. The synthesized polymers exhibited glass transition temperatures in the range of 167-228 degrees C, thermal stability with decomposition temperatures in the range of 275-446 degrees C, and excellent solubilities in common organic solvents. The light-induced optical anisotropy was studied in obtained azopolymers with the help of a holographic grating recording technique. Two polarization geometries were applied for the grating inscription s-s and p-p. The influence of the polarization geometry on the diffraction efficiency dynamics and on the depth of the surface modulation was not observed, which is different from results reported in the literature. Surface relief gratings, which appeared after the light exposure, were observed by atomic force microscopy. Additionally, the optical anisotropy in poly(esterimide)s was investigated by photoinduced birefringence measurements. For the first time, in polyimide with covalently bonded azobenzene derivatives, the high photoinduced birefringence (Delta n = 0.01) was measured.

Dynamic Polarization Holography: Methods and Applications

The results of investigations of kinetics of photoanisotropy induction and relaxation in polarization-sensitive media with conformation-orientation mechanism of the anisotropy induction having significant dark relaxation are presented. It is shown that such materials can be applied for tasks of dynamic polarization holography. With the purpose of improvement dynamic characteristics of polarization-sensitive materials azodye Nitrodimethyl red (NDMR) is specially synthesized. Materials on the basis of NDMR are used for recording dynamic polarization-holographic gratings with different profile of anisotropy. The results of the investigation of kinetics of diffraction efficiency (DE) of these gratings and the analysis of polarization state of diffracted orders are given. It is shown that time of a cycle of recording/erasing for gratings of some types is of the order of 100 ms at DE = 21 %. The theoretical model of dynamic polarizationholographic recording on such materials is presented. Possible applications of the methods of dynamic polarization holography are discussed.

Three gratings coupling during the holographic grating recording process in azobenzene-functionalized polymer

The authors present a mechanism explaining complex diffraction efficiency dynamics of the holographic grating recording process in azobenzene-functionalized polymer. The mechanism assumes simultaneous formation of three coupling phase gratings with different recording time constants and constant, equal to 0 or π, phase shifts between them. Two of gratings originate from the refractive index changes in the bulk of material and the third one from the surface relief modulation. Diffraction efficiency dynamics curves calculated using the proposed model are in a very good agreement with the experimental results.

Effect of reconstruction beam polarization on the kinetics of anisotropic gratings in bacteriorhodopsin

Anisotropic gratings are recorded on bacteriorhodopsin films by two parallelly polarized beams, and the effect of the polarization orientation of the reconstructing beam on the diffraction efficiency kinetics is studied. A theoretical model for the diffraction efficiency kinetics of the anisotropic grating is developed by combining Jones-matrix and photochromic two-state theory. It is found that the polarization azimuth of the reconstructing beam produces a cosine modulation on the kinetics of the diffraction efficiency, being positive at the peak efficiency and negative for steady state. By adding auxiliary violet light during grating formation, the saturation of the grating can be restrained. As a result, the negative cosine modulation for the steady-state diffraction efficiency changes to a positive one. In addition, the steady-state diffraction efficiency is increased appreciably for all reconstructing polarization orientations.

Influence of auxiliary violet light on holographic kinetics at low and high recording intensities in bacteriorhodopsin film

The photochromic bacteriorhodopsin (BR) film can be used as a rewritable holographic recording medium. Due to the saturation absorption and the scattering and reflecting lights from the BR film, the grating contrast-ratio of the hologram is diminished during the hologram recording. When the intensity of the recording light is low, the influence of the saturation absorption and the scatter and reflection of BR film on the grating contrast-ratio is weak. But for the case of intense recording light, this influence is more serious. It is found that the influence of the auxiliary violet light on the holographic kinetics of diffraction efficiency is distinct under different recording intensities. At the low recording light intensity, the steady diffraction efficiency is increased and the peak diffraction efficiency is suppressed by the auxiliary violet light. But for intense recording light, the steady diffraction efficiency and the peak diffraction efficiency are both increased by the auxiliary violet light. Based on the two-state model of BR photochromism, we give a good theoretical explanation to the above phenomena.

Influence of auxiliary violet light on holographic diffraction efficiency under different recording intensities in bacteriorhodopsin film

The photochromic bacteriorhodopsin (BR) film can be used as a rewritable holographic recording medium. Due to the scattering and the reflecting of light from the BR film, the grating contrast of the hologram is diminished during the hologram recording. When the intensity of the recording light is weak, the influence of the scattering and reflection on the grating contrast is low enough to be neglected. But in the case of intense recording light, this influence should not be overlooked. It is found that the influence of the auxiliary violet light on the holographic diffraction efficiency kinetics is distinct under different recording intensities. At weak recording light intensities, the steady diffraction efficiency are increased and the peak diffraction efficiency is suppressed by the auxiliary violet light. But for intense recording light, the steady diffraction efficiency as well as the peak diffraction efficiency are both increased by the auxiliary violet light. Based on the two-level model of BR photochromism, we give a good theoretical explanation to the above phenomena.