Photoinduced Changes In Optical Properties Research Articles

Photoinduced modification of optical properties of ferroelectric PZT thin films

This study investigates ultrafast photoinduced changes in optical properties of ferroelectrics (PZT) on femtosecond to nanosecond timescales, using broadband transient reflectivity studies. Surprisingly, spectral features were observed below the bandgap, which could not be attributed to ground state bleaching, excited state absorption, and/or stimulated emission. A model based on probe energy independent changes in refractive index and extinction coefficient showed good agreement with experimental results. Three relaxation processes were phenomenologically considered for the temporal evolution. Laser-induced heating was ruled out as the cause of short timescale behavior and photorefractive effect was suggested as a potential mechanism for changes in the optical properties.Graphical abstract

Photoinduced mass transport in azo compounds

The photoinduced changes of optical properties in azobenzene containing compound thin films were studied under influence of polarized and non-polarized 532 nm laser light. Under influence of light azo compounds experience trans-cis isomerisation process, that can be observed in the absorbance spectrum of the sample. If the light is linearly polarized, molecules align perpendicularly to the electric field vector and as a result photoinduced dichroism and birefringence is obtained. If a known lateral polarization modulation of the light beam is present, mass transport of the azobenzene containing compound occurs. By measuring the surface relief with a profilometer the direction of mass transport can be determined. The studies of this work show that direct holographic recording of surface relief gratings can be used in optoelectronics, telecommunications and data storage.

Azodyed gelatin films for holographic recording

In this work we present a preparation method of azo-dyed gelatin thin films for holographic recording and their photoinduced changes of optical properties. The non-toxic, commercially available and cheap ingredients were used for film preparation. The films were prepared by mixing azo-dyes with gelatin solution.The photoinduced properties of prepared films were investigated. The photoinduced dichroism and birefringence at 532nm laser radiation were observed. The holographic recording of surface and volume gratings by 532nm wavelength laser radiation were performed and surface relief gratings were studied with AFM. The mass transport direction in azodyed gelatin was studied.

Search for the Photo-Induced Hidden Phase in Inorganic and Organic Systems

Search for the Photo-Induced Hidden Phase in Inorganic and Organic Systems S. Koshiharaa,∗, K. Onda, Y. Okimoto and T. Ishikawa JST, CREST & Department of Materials Science, Tokyo Institute of Technology Meguro-ku Tokyo 152-8551, Japan Department of Environmental Chem. and Engineering, Tokyo Institute of Technology Nagatsuta-Yokohama, 226-8503, Japan We review the dynamical behavior of strongly electron–lattice (orbital) coupled system induced by photo-excitation of fs laser pulse. By virtue of the femtosecond (fs) spectroscopy and picosecond (ps) time-resolved X-ray diffraction measurements, we demonstrate that the photo-irradiation creates new ordered state so called as “hidden phase” which can never be realized under thermo-equilibrium condition. This exotic phase commonly plays the key role for realizing the gigantic photo-induced changes in optical properties of inorganic and organic electron–lattice strongly coupled systems.

Photoinduced changes in optical properties of Ga–Sb–Ge–Se glasses

The kinetics of photoinduced effects on Ga 5Sb 10Ge 25Se 60 thin film exposed to continuous wave laser radiations are studied as a function of exposure time and laser intensity. The transmission and reflection spectra of thin films before and after exposure are investigated. The optical band gap and the refractive index are derived from the above spectra. Generalized Miller's rule and linear refractive index are used to find the nonlinear susceptibility and nonlinear refractive index of the thin films. The studies show a red shift in the band gap with increase in exposure time and laser power which is attributed to the photoinduced darkening in the films.

Formation of Direct Surface Relief in Photochrome-Chalcogenide Composites

Formation of Direct Surface Relief in Photochrome-Chalcogenide CompositesA method for preparation of thin triple composite films of organic polymer-chalcogenide-photochromes is described, the photo-induced changes of optical properties and holographic recording are considered. The films were obtained from solutions of arsenic sulphide, azobenzene Disperse Red 1, spiropyran, and organic polymers in organic solvents. The solutions were spread over glass or quartz substrates; the thickness of dry films was 3-10 μm. The absorption spectra of the prepared films were studied and analyzed. The holographic recording of diffraction gratings was performed by laser lines of 325 nm, 442 nm and 532 nm. During recording the diffraction efficiency was measured simultaneously in the transmission and reflection modes. The relief formation on the film surface was observed and the profile of the gratings formed was analyzed using AFM microscope. The influence of photoisomerization and photo-induced mass transport on the surface relief formation process is discussed.

Photostructural reconstructions of As-S and As-Se semiconductor glasses

The results of experimental investigation of photoinduced changes in optical properties of semiconductor glasses of the As-Se and As-S systems are presented. With using the data of the Mossbauer emission spectroscopy on the 129Te(129I) isotope, the observed changes in optical properties can be attributed to the reconstruction of the glass matrix under the effect of radiation.

Photo-induced changes in optical properties of As 2 S 3 and As 2 Se 3 films deposited at normal and oblique incidence

Photostructural transformations in amorphous chalcogenide films have been a subject of intensive research so far. In this paper we discuss the changes in the optical properties of typical As-based chalcogenide glasses (As2S3 and As2Se3) on exposure to ultraviolet (UV) light. An attempt has been made to systematically investigate the optical parameters like extinction coefficient, refractive index and optical bandgap of the films by measuring the same for as-grown and UV-exposed amorphous films of As2S3 and As2Se3 prepared by vacuum evaporation technique.

Photoinduced changes of optical properties of amorphous chalcogenide films at ambient air pressure

It is shown that Ge 30Se 70 and As 38S 62 amorphous films are relatively stable against photooxidation. The Ge 35S 65 film is easily photooxidized as indicated by an increase of absorption around 825 and 690 cm −1/due to the presence of the Ge-O bonds/. It is accompanied by irreversible bleaching. Vacuum annealed Ge 35S 65 film is also bleached. This bleaching, however, is accompanied only by an increase of Ge-S bonds density, thus it is an intrinsic effect indeed.

Model of photoinduced changes of optical properties in amorphous layers and glasses of Ge-Sb-S, Ge-S, As-S and As-Se systems

Photoinduced changes of transmittance /Δt/ and reflectance /Δr/ of thin layers, glasses and glassy powders of systems Ge-Sb-S, Ge-S, As-S and As-Se were studied. For explanation of experimental results a model is suggested which implies both the redistribution of chemical bonds and the compactness of the structure.

Photoinduced changes in optical properties of obliquely deposited As 2S 3, As 2Se 3 and As-Se-Ge films

Photoinduced changes in the absorption edge and refractive index of 0° and 80° angle-of-incidence deposited As 2S 3, As 2Se 3 and As-Se-Ge films have been investigated in the vicinity of the absorption edge. No appreciable effect of oblique deposition has been observed in As 2X 3 ( X = S, Se). There are large irreversible changes, however, on exposure of As-Se-Ge films deposited at 80° incidence. The enhancement of photo-effects on addition of Ge in obliquely deposited films is primarily due to the large photoinduced volume changes.

Ellipsometry of tetragonal lead oxide single crystals

The refractive index of PbO tetragonal single crystals ( n ̄ 0 = 2.73±0.05 ) and parameters of thin dielectric film on their real surfaces ( n f = 1.56±0.01, d = 10−85 A ̊ ) have been measured by the method of ellipsometry at λ = 6328 A ̊ . For the first time the photo-induced changes of optical properties of PbO ( t) surface film have been observed.