Photoinduced phenomena in amorphous As<Subscript>4</Subscript>S<Subscript>3</Subscript>Se<Subscript>3</Subscript>–Sn films

We investigate the kinetics of photodarkening and recording of holographic diffraction gratings in amorphous As₄S₃Se₃ thin-film structures doped with tin (Sn) in concentrations of 0–10 at %. It is established that an increase in the Sn concentration leads to a decrease in the photodarkening rate and degree. The photodarkening kinetics is approximated by a stretched exponential function. It is found that an increase in the Sn concentration leads to a decrease in the transmission (photodarkening) variation in the investigated As₄S₃Se₃–Sn films. It is determined that, in the recording of holographic diffraction gratings at a Sn concentration of 3–8 at %, the As₄S₃Se₃–Sn films exhibit the maximum sensitivity and diffraction efficiency of the recorded gratings. It is shown that the dependence of diffraction efficiency on the As₄S₃Se₃ film thickness has the maximum at a film thickness of 4 µm.     

Image recording on photothermoplastic media with different thicknesses of the thermoplastic layer

The quality of images recorded on photothermoplastic media (PTPMs) with various thicknesses of the thermoplastic layer is investigated. It is found that the potential of a corona-forming electrode initiating deformations on a PTPM surface and the diffraction efficiency, corresponding to the additional maxima in its dependence on the spatial frequency, increase with decreasing thickness of the thermoplastic layer, in contrast to the diffraction efficiency at the resonance frequency. It is shown that the frequencies corresponding to additional maxima in the dependence of the diffraction efficiency on the spatial frequency are preferable for application as the carrier frequency for raster-scan recording and as the center carrier frequency for holographic image recording on PTPMs in order to reach a higher diffraction efficiency, image contrast, and signal-to-noise ratio than those attainable at the resonance frequency. An anomalous relation between the resolution and sensitivity of PTPMs is found under the suggested recording conditions and carrier frequencies. It is shown that both the resolution and the sensitivity of PTPMs increase with decreasing thickness of the thermoplastic layer.     

Thermal regeneration of activated carbons saturated with ortho- and meta-chlorophenols

Activated carbons (ACs) made from peach and plum stones were oxidized and impregnated with salts of Cu(II), Fe(III), Ni(II) and Cr(III). The chemically modified ACs, along with a commercial AC (S208c), were saturated with ortho- (OCP) and meta-chlorophenol (MCP) to investigate the potential for thermally regenerating the spent ACs. The thermal regeneration process was monitored by thermal analysis (TGA/DSC), gas chromatography and mass spectrometry (GC/MS). Thermal desorption profiles showed that in most cases weight losses occur in two steps (weak physisorption at ∼220 °C and strong chemisorption at ∼620 °C). Intermediate steps at ∼400 °C appeared in samples whose chemical treatments successfully weakened the interactions between strongly chemisorbed chlorophenol (CP) molecules and AC surfaces. The type and quantity of products of OCP and MCP desorption during the thermal regeneration of a spent AC depend on the chemical modification given to the AC prior to its use as CP adsorbent. Besides the original chlorophenols, thermal regeneration products can include chlorobenzene, dichloro-dibenzofuran, phenol, aliphatic and aromatic hydrocarbons, water, chlorides, carbon oxides, hydrogen, and char deposits. Mechanisms for the formation of these compounds are discussed. The char deposits built during this study did not appear to diminish the surface area or porosity of the chemically modified ACs following their thermal regeneration.     

Diffraction efficiency and light-scattering power of photothermoplastic holographic gratings

The diffraction efficiency and light-scattering power of holographic gratings formed on the surface of a two-layer photothermoplastic carrier with a pit structure of deformation are studied. The influence of the height and regularity of the pit deformation on the diffraction efficiency and light-scattering power is studied. It is shown that the pronounced resonance character of the dependence of the diffraction efficiency on the spatial frequency in the case of pit deformation is related to the distribution of the deformation depth over spatial frequencies; however, the dominant factor is the mutual arrangement of pits within the interference fringe. It is found that the light-scattering power is determined for the most part by the size and density of the deformation. A new method is proposed for determining the resolution of photothermoplastic carriers with pit deformation, which apparently can be used for photothermoplastic carriers with any irregular structure of deformation. This method is based on the analysis of the dependence of the light-scattering power of holographic gratings on their spatial frequency. It is shown that the resolution depends inversely proportionally on the thickness of the thermoplastic layer of the optical carrier.     

Effect of corona discharge on formation of holographic diffraction gratings in the Cu–As<Superscript>2</Superscript>Se<Superscript>3</Superscript> thin-film structure

Application of negative corona discharge in the course of recording leads to an increase in the holographic sensitivity of the Cu–As₂Se₃ structure and diffraction efficiency of the recorded holographic gratings and the relief gratings fabricated with the aid of chemical etching. Positive corona discharge impedes the recording of holographic gratings in the Cu–As₂Se₃ structure. The Cu–As₂Se₃ structure exhibits the properties of a negative photoresist under irradiation in the presence of the negative corona discharge. In addition, the dissolution selectivity substantially increases due to the corona discharge.     

Effect of Corona Discharge on the Optical Properties of Thin-Film Cu–As2Se3 Structures

Optics and Spectroscopy - The effect that corona discharge has on holographic recording of diffraction gratings in a thin-film Cu−As2Se3 structure deposited on glass by thermal vacuum...     

Variation of parameters of pit deformation when recording holograms of a planar wavefront

Variation of the deformation structure of the surface of a photothermoplastic carrier is demonstrated in the case where high frequencies of an interference pattern are recorded. A smooth variation of the period of a grating projected is shown to lead to a variation of the pit diameter in a limited frequency range. A high-frequency maximum of the diffraction efficiency is observed for the deepest pits formed with the highest probability, but their size coincides neither with the maximum nor with the minimum diameter. Periodic repetition of the curve of pit growth with decreasing frequency forms additional maxima in the frequency dependence of the diffraction efficiency at frequencies corresponding to the alignment of resonant dimensions of pits in one, two, and three rows.     

On the Fresnel diffraction pattern of phase holographic gratings

The Fresnel diffraction pattern of phase diffraction gratings is studied on the example of idealized sinusoidal relief-phase plane holographic thermoplastic gratings. It is shown that, in the region of low spatial frequencies, which are more than two times lower than the inverse wavelength of the reading coherent radiation, the intensities of the main diffraction maxima, the diffraction efficiency, and the light-scattering power are independent of the spatial frequency of the phase gratings under investigation, which are characterized by a sinusoidal law of modulation of the reading-radiation phase. It is established that the range of spatial frequencies at which a plateau is observed in these dependences increases with decreasing amplitude of the phase modulation of the reading light. These dependences are also observed to have similar character for the thermoplastic holographic gratings under study. Calculations were performed to analyze the influence of real profiles of thermoplastic strain on the diffraction efficiency and light-scattering power of such gratings. On the basis of analysis of the results obtained, recommendations on using holographic and raster techniques of recording data on phase carriers are given that make it possible to improve the quality of the restored optical image.     

Pore structure and adsorption properties of stone active carbons prepared by physicochemical and chemical activation methods

Active carbons (ACs) with diverse microporous and developed mesoporous structures were prepared by chemical and phisochemical activation methods from walnut shells, fruit stones, and grape seeds. The surface chemistry was studied by chemical titration and spectroscopy in the IR, UV, visible, and near IR regions. The ACs prepared by chemical activation contain carboxyl and phosphate groups, which impart acidic properties to the surface. Basic functional groups are mainly formed on the ACs prepared by physicochemical activation. The AC surface has a complicated chemical composition, which results in high adsorpion activity. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 744–748, May, 2006.     

Charging of glassy chalcogenide semiconductors in corona discharge and its effect on holographic grating formation

Recording of optical holographic gratings based on photostructural transformations in thin (≈ 1 μm) As₂S₃ and As₂S₃ semiconductor layers in the presence and absence of a corona discharge and also chemical etching of these gratings are studied. Initiation of a corona at the stage of interference grating recording is shown to improve the exposure contrast of metal-glassy chalcogenide semiconductor thin-film structures. The holographic sensitivity, diffraction efficiency, dynamic range, and contrast are also improved severalfold. When phase relief gratings formed in these layers are selectively etched in a chemical etchant in the presence of a corona, their profile becomes more regular and deeper by 25–30% and the diffraction efficiency increases by 30–50%.