0000000000114661
AUTHOR
Andris Ozols
Influence of the age of amorphous nonannealed As2S3 thin films on holographic properties
The dependences of the maximal first order diffraction efficiency and the corresponding specific recording energy on the holographic grating period were studied. Grating period was varied from 0.40 to 70.0 μm. Both fresh and aged films were used. A large holographic recording efficiency decrease in the course of aging is found to take place. These changes are due to the effective film grain size increase caused by the relaxational structural changes and atmospheric oxygen exposure. Results are explained with the aid of stress fields induced by the evaporation and holographic recording. The obtained results can be used to optimize the hologram recording in amorphous chalcogenide films.
Model of holographic recording in amorphous chalcogenide films using subband-gap lightat room temperature
The subband-gap light holographic recording in amorphous as-evaporated ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ films at room temperature is experimentally studied. Properties are considerably different from those of usual holographic recording based on the band-gap light induced structural changes. The most important characteristic features of this nonpermanent recording include photoinduced refractive index increase, weak photobleaching, the absence of the photoinduced thickness changes, light polarization dependence, large exposures, holographic grating shifts during the exposure and a peculiar two maxima spatial frequency response. The first order diffraction efficiency up to 4.1% is achie…
<title>Theoretical and experimental studies of light diffraction anisotropy by holograms in a-As-S-Se films</title>
Diffraction anisotropy (DA) defined as the polarization dependence of the amplitudes (amplitude DA) and phases (phase DA) of the diffracted light waves is studied in the case of a sinusoidal transmission amplitude-phase grating both theoretically and experimentally. Theoretical analysis was mainly based on the Kogelnik's coupled wave theory (KCWT) and also on the conclusions of rigorous coupled wave theory (RCWT) and effective medium theory (EMT). Experimentally gratings with 0.42 μm period in a-As-S-Se films at 632.8 nm were studied. KCWT predictions were compared with those of RCWT and EMT as well as with the experimental DA results. It is found that KCWT properly describes the first orde…
<title>Phase conjugation properties of a-As-S-Se films</title>
Light wavefront inversion (phase conjugation) in a-As-S-Se films has been studied experimentally. Phase conjugation (PC) of plane and spherical waves is carried out in a-As40S15Se45 films using degenerate four-wave-mixing (DFWM) geometry at 633 nm. In the plane wave case simultaneous PC efficiency and DE measurements have been made versus exposure time, light intensity and holographic grating period. The maximal PC efficiency was 2.3% and the minimal PC specific recording energy was 2 J/(cm2%) whereas the maximal DE was 0.9% and the minimal specific hologram recording energy was 10 J/(cm2%). The optimal grating period was 2 μm. When compared to a-Se films a-As-S-Se films exhibit lower PC ef…
<title>Mechanisms of holographic recording in amorphous semiconductor films</title>
The mechanisms of holographic recording in (mainly chalcogenide) amorphous semiconductor films are reviewed including photoinduced structural changes, relaxational structural changes, recharging of localized states in the band gap, and photoinduced anisotropy. The holographic properties in these cases are compared. Different effects of hologram self-enhancement are also considered.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
<title>Hologram recording in azobenzene oligomers</title>
Elementary hologram (holographic grating) recording and their coherent optical erasure have been experimentally studied in azobenzene oligomer (ABO) layers differing by their chemical composition, matrices and by the connection type of azobenzene chromophores to the matrix (dispersed or covalently bound). The best holographic parameters (7.9% diffraction efficiency and 86 J/cm2 specific recording energy) were achieved in the samples with covalent bonding to the matrix. Vector recording is also possible. Recording is unstable and reversible. The coherent optical erasure studies have shown its efficiency dependencies on the initial diffraction efficiency, erasing beam intensity and grating pe…
<title>Photoinduced anisotropy and holographic recording in amorphous chalcogenides</title>
The effect of photoinduced anisotropy and its application to vector hologram recording is reviewed focusing on amorphous chalcogenides. Vector holographic grating recording in amorphous As-S-Se(a-As-S-Se) films is experimentally studied and analyzed in comparison with scalar recording. It is holographically established that a linearly polarized 632.8 nm light produces photoinduced anisotropy and the chalcogen related D+, D- center reorientation and generation mechanism is proposed. It is used to explain the observed peculiarities of vector recording in comparison with scalar recording based on photoinduced structural changes: much lower diffraction efficiency (4 X 10-3% versus 4%), much lar…
<title>Holographic properties of dielectric crystals and amorphous semiconductor films</title>
Holographic recording properties and mechanisms are analyzed and compared in dielectric electrooptic crystals (EOC), dielectric colored alkali halide crystals (AHC) and amorphous semiconductor films (ASF) basing on author's investigations as well as on the literature data. Holographic photosensitivity parameters are introduced enabling the characterization of the recording mechanism efficiency independently of the particular optical and geometrical sample parameters, and allowing also for recording optimization. Ultimate specific recording energies for EOC, AHC and ASF are theoretically estimated. It is concluded that the ultimate recording energy for both crystalline and amorphous material…
Effect of structure relaxation on the holographic recording in amorphous As2S3 films
Abstract Results of the experimental studies of holographic recording in a-As 2 S 3 films, such as exposure and intensity dependences, spatial frequency dependence, are reported. Several peculiarities are found including recording intensity threshold, nonmonotonical intensity dependences, nonlinear exposure curves, the change of the spatial frequency response due to film aging. These peculiarities are explained in terms of the phenomenological model which is based on the simultaneous action of the photostructural changes and the relaxational structural changes.
Holographic recording of surface relief gratings in tolyle-based azobenzene oligomers
Abstract Holographic recording of surface relief gratings (SRG) in tolyle-based azobenzene oligomer films have been carried out at 514.5 nm. It was experimentally studied by spectroscopic and AFM methods. The maximum surface modulation amplitude was 35 nm. SRG formation is explained by the mean-field model and by the photodegradation of chromophores enabling the directional mass transport as the result of trans–cis transformations. The conclusion is made that SRG are stable but the diffraction efficiency (DE) changes are due to the complementary decaying amplitude-phase gratings. Strong polarization dependences of transmitted and reflected DE are found. They are explained by the diffraction…
Thermal, glass-forming, nonlinear optical and holographic properties of "push-pull" type azochromophores with triphenyl moieties containing isophorene and pyranylidene fragments
Molecular organic compounds with electron donating fragment bounded through π-conjugated system with electron acceptor fragment, as well as with incorporated triphenyl groups in their molecules show potential for creating cheap and simple solution processable materials with nonlinear optical properties. Additional insertion of azobenzene fragment in their structures makes them also possible to form holographic volume and surface relief gratings (SRG) after exposure to laser radiation, which could be useful for holographic data storage. For these purposes polymers are generally used. However, their application is complicated and challenging task as in every attempt to obtain the same polymer…
<title>Effects of light polarization and crystal orientation on the holographic recording efficiency in doped LiNbO<formula><inf><roman>3</roman></inf></formula> crystals</title>
The holographic recording efficiency in doped LiNbO3 crystals has been studied both experimentally and theoretically depending on the type of dope, on the recording geometry and on the polarizations of the recording and readout light.. The studied crystals can be arranged in the following order by their efficiency: LiNbO3:Cu, LiNbO3:Fe (yet having a smaller thickness and donor concentration than LiNbO3:Cu), LiNbO3:Fe+Cu, LiNbO3:Fe+Ti, LiNbO3:Ti. It was found that the recording geometry with the holographic grating vector along the optical axis is much more efficient than in the perpendicular configuration.This fact is in accordance with the photorefraction theory based on photogalvanic and …
Polarization holograms and diffraction anisotropy in amorphous chalcogenides
Polarization hologram recording based on the effect of photoinduced anisotropy (PA) is reviewed, focusing on amorphous chalcogenides (ACh). Possible PA mechanisms in ACh are considered. Polarization holographic grating recording in amorphous As?S?Se (a-As?S?Se) films is experimentally studied and analysed in comparison with scalar recording. It is holographically established that linearly polarized 632.8 nm light produces photoinduced anisotropy and the chalcogen related D+, D? centre reorientation and generation mechanism is proposed. It is used to explain the observed peculiarities of polarization (vector) recording in comparison with scalar recording based on photoinduced structural chan…
<title>Holographic recording in amorphous semiconductor films</title>
The present state of the real time holographic recording in amorphous semiconductor films is reviewed including mechanisms, parameters, properties and applications. Effects of the coherent, incoherent and relaxational self- enhancement as well as the influence of the film structure relaxation are considered. Quasi-permanent sub-band-gap light holographic recording is reported for the first time. 157
Diffraction-efficiency oscillations in amorphous As_2S_3 films
An experimental study of the holographic gratings recorded in nonannealed, thermally with time relaxed amorphous As2S3 films by 514.5-nm light in the presence of 632.8-nm readout light is carried out. The dependences of the maximal first-order diffraction efficiency on the holographic grating period was studied in a wide range of periods, from 0.40 to 70.0 µm. A peculiar oscillatory diffraction-efficiency temporal behavior occurring under certain conditions is reported. The obtained results are discussed in terms of photoinduced structural changes, relaxational structural changes, photoinduced anisotropy, and photoinduced recharging of the localized states in the bandgap. The diffraction-ef…
Holographic properties of azobenzene oligomers with differently bonded chromophore groups
Holographic properties of two types (I and II, specified in the text) of azobenzene oligomers (ABO) have been experimentally studied in the spectral region of low absorption at 633 nm. In the case of type I ABO the chromophore groups were covalently bonded to either tolyl-polyurethane or hexamethylene-polyurethane matrix. In the case of type II ABO azobenzene chromophores were dispersed in polystyrene matrix, and their concentration was varied from 0.005 to 0.200 mol/l. Samples were in the form of 10 µm thick films. In both cases the diffraction efficiency exposure time dependences were measured for the holographic grating period of 2 (m at 633 nm. The diffraction efficiency of more than 2%…
<title>Sub-bandgap light hologram recording in amorphous chalcogenides</title>
Sub-bandgap light recording (SBLR) of holograms is studied basing on the experiments in a-As2S3 films and literature data. Holographic grating recording with focused (light intensity I = 14 - 124 W/cm2 ) and unfocused (I = 0.50 - 0.78 W/cm2) 632.8 nm He-Ne laser sub-bandgap light in non-annealed and annealed a-As2S3 films has been experimentally studied. The focused light recording is found to be much more efficient (diffraction efficiency up to 14.9%, specific recording energy down to 216 J/(cm2%)) than the unfocused light recording (0.11%, 72400 J/(cm2%)). Some other properties are also different. The focused light recording is explained by the photothermally stimulated relaxational struc…
Triphenyl group containing molecular glasses of azobenzene for photonic applications
Abstract D-π-A type organic molecules have attracted considerable attention of scientists due to their potential applications in nonlinear optics and holographic data storage as light, flexible and low-cost photonic materials. To provide a better understanding on the relation between the compound chemical structure and their physical properties necessary for the mentioned purposes, eight glassy triphenyl group containing derivatives of azobenzene with incorporated 5,5-dimethylcyclohex-2-enylidene or 4H-pyran-4-ylidene structural fragments and dicyanomethylene, indene-1,3-dione and pyrimidine-2,4,6(1H,3H,5H)-trione acceptor groups have been synthesized and investigated. Thermal stability of …
<title>Angular selectivity of thin gratings</title>
The angular selectivity of thin gratings is studied both experimentally and theoretically. The concepts of thick and thin gratings are analyzed. Thin holographic gratings recorded in a-As-S-Se films have exhibited pronounced and oscillatory diffraction efficiency angular dependences. These results are explained by the obliquity factor in Fresnel-Kirchhof diffraction integral and by finite beam and grating sizes. It is also shown that oscillatory diffraction efficiency angular dependences, most probably, arise due to the interference of diffracted waves of different orders because dephasing can be significant for small grating strengths and large enough readout angles. Fabry-Perot resonator …
<title>Structure-relaxation-induced peculiarities of the holographic recording in amorphous As<formula><inf><roman>2</roman></inf></formula>S<formula><inf><roman>3</roman></inf></formula> films</title>
The results of the experimental study of holographic recording in a-As2S3 films are reported such as exposure and intensity dependencies, spatial frequency dependence. Several peculiarities are found including recording intensity threshold, nonmonotonical intensity dependencies, nonlinear exposure curves, the change of the spatial frequency response due to films aging. These peculiarities are explained in terms of phenomenological model which is based on the simultaneous action of the photostructural changes and the relaxational structural changes.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Structure optimization of azobenzene oligomers for holography
Azobenzene oligomer layers with side chain chromofore groups (ChG) has been experimentally studied to optimize scalar and vector hologram recording at 633 nm. ChG with different acceptors (Br, NO2, H, CN) and different bonding type to the matrix (dispersed without bonding or with covalent bonding) were used. The influence of oligomer matrix (polyvinylbuthirol, tolyle, hexamethylene, polyvinylpirolidone, double matrix) and spacers was also studied. The best results (the maximal diffraction efficiency of 7.9% and the minimal specific recording energy of 0.38 J/(cm2 %)) are obtained for ChG with one NO2 acceptor group covalently bonded to tolyle matrix. Double matrix considerably decreases the…
Spatially resolved optical studies of F-center diffusion in KBr crystals.
Spatially resolved optical studies of F-center diffusion during and after the photothermal F\ensuremath{\rightarrow}X color center conversion have been performed by optical scanning and holographic methods in electrolytically colored KBr crystals. Average velocities and diffusion coefficients of F centers have been determined for Gaussian and periodical spatial exposing light intensity distributions. A strong influence of the light intensity gradient has been found on F-center diffusion. It manifests itself by a rapid increase of the effective diffusion coefficient when the light intensity gradient is decreased. This behavior allowed us to explain the observed peculiarities of the holograph…
Two-color holographic-grating formation in amorphous As_2S_3 films
A detailed experimental study of the holographic gratings recorded in nonannealed amorphous As2S3 films by 514.5-nm light in the presence of 632.8-nm readout light is carried out. A strong influence of a continuous 632.8-nm readout is found. The dependences of the maximal first-order diffraction efficiency and the corresponding specific recording energy on the holographic grating period were studied in a wide range of periods from 0.40 to 70.0 μm for 2-yr-old films. The obtained results are discussed in terms of photoinduced structural changes, relaxational structural changes, photoinduced anisotropy, and photoinduced recharging of the localized states in the bandgap. The photoinduced sulph…