Matvei Klebanov

Photoinduced phenomena in spin-coated vitreous As2S3 and AsSe films

Abstract Vitreous As2 S3 and AsSe films are prepared by the spin-coating technique from solutions of corresponding chalcogenide glasses in amines. The following photoinduced optical phenomena in the films are revealed and investigated: photodarkening, photoinduced linear dichroism, photodiffusion of silver and polarized photodoping. The photoinduced processes in the spin- coated films are compared with those observed in evaporated films of the same composition.

Novel effects in inorganic As50Se50 photoresists and their application in micro-optics

Some novel properties of one-layer inorganic As50Se50 photoresists are demonstrated. The photosensitivity of the photoresists increases drastically (1000 times and more) upon exposure to short intense light pulses. The exposure characteristics can be changed from steep to gently sloped ones. The photoresists can be used effectively in both negative and positive modes. Combination of these properties with good optical properties such as a high refractive index, high transparency in the IR and high resolution, makes As50Se50 photoresists attractive for application in nonconventional optics. Close packed spherical and cylindrical microlens arrays for IR based on the As50Se50 photoresists are fabricated and tested. The advantage of this technique is in the elimination of thermal reflow and plasma etching that are commonly used.

Kinetics of the photostructural changes in a-Se films

The kinetics of the photodarkening effect has been studied experimentally for amorphous selenium (a-Se) layers at room temperature and at an elevated temperature (35°C) close to the glass transition. By switching an intense pumping light on and off with a period of 100s, we have studied the kinetics of both the buildup of photodarkening and its relaxation (recovery). It was found that at 35°C, only a reversible component of photodarkening has been observed. This result has been interpreted within the framework of a phenomenological model assuming that photodarkening is caused by light-induced transitions of structural units from their ground states into metastable states. Our estimate for the energy barrier EB between these states obtained for the photodarkening process (EB∼0.8eV) coincides with that obtained from the analysis of the relaxation process. At room temperature, an irreversible component of photodarkening has been observed along with the reversible one. The energy barrier responsible for the r...

Stimulated Brillouin scattering amplification in centimeter-long directly written chalcogenide waveguides

Stimulated Brillouin scattering (SBS) amplification is obtained in directly written As2S3 channel waveguides. Centimeter-long waveguides were written using a Ti:sapphire femtosecond laser, operating at a central wavelength of 810 nm. The cross-section of the waveguides was of 4u2009u2009μm×1u2009u2009μm. A Brillouin frequency shift of 7.5 GHz is observed, in general agreement with corresponding previous studies. The SBS gain spectrum in the short waveguides is comparatively broad, with a full width at half-maximum of 200 MHz. We attribute the broad linewidth to the spatial evolution of the electromagnetic field profile along the waveguide.

Laser-induced phenomena in chalcogenide glassy films

Abstract Laser-induced optical phenomena in binary and three-component chalcogenide glassy films of Asue5f8Seue5f8Te and Geue5f8Asue5f8S systems are studied. Large increase of photosensitivity of photoinduced structural transformations in case of excitations by short intense laser pulses and photosensitivity shift to IR range were revealed. Some peculiarities in kinetics of appearance and reorientation of laser-induced linear dichroism are observed and conclusions about the mechanism of this phenomenon are made. Some applications of chalcogenide films in electrooptics are discussed.

Appearance and reorientation of photoinduced anisotropy in chalcogenide glassy films

Abstract The kinetics of appearance and reorientation of photoinduced dichroism (a manifestation of photoinduced anisotropy) is studied in chalcogenide glassy films by means of the polarization modulation technique. Two distinct processes are identified: creation of photoinduced defects and photo-stimulated orientation of defects both native and photoinduced. Of these processes, the first one can be carried out by both unpolarized and polarized radiation and has much larger time constant than the second. The annealing temperatures of the two effects are also different. In all of materials studied (AsSe, Ge2Pb1S4, Se) the effect of photoinduced anisotropy was shown to be a one-photon process. Unusual behavior of dichroism in partially crystallized Se films is revealed.

Anisotropy of photoinduced light-scattering in glassy As2S3

Abstract Quantitative data on photoinduced light-scattering anisotropy and its reorientation in bulk As 2 S 3 glass are presented together with data on transmittance anisotropy. The photoinduced rotation of the polarization plane and photoinduced ellipticity for scattered light and also the fatigue of anisotropy reorientation are shown. It is concluded that the generation of scattering centers is the process which determines the whole group of photoinduced vectoral phenomena in chalcogenide glasses.

High-Q ring resonators directly written in As 2 S 3 chalcogenide glass films

Planar ring resonator waveguides are fabricated in thin films of As2S3 chalcogenide glass, deposited on silica-on-silicon substrates. Waveguide cores are directly written by scanning the focused illumination of a femtosecond Ti:sapphire laser at a central wavelength of 810xa0nm, through a two-photon photo-darkening process. A large photo-induced index change of 0.3–0.4 refractive index units is obtained. The radius of the ring resonator is 1.9xa0mm, corresponding to a transmission free spectral range of 9.1xa0GHz. A high loaded (intrinsic) Q value of 110,000 (180,000) is achieved. The thermal dependence of the resonator transfer function is characterized. The results provide the first report, to the best of our knowledge, of directly written high-Q ring resonators in chalcogenide glass films, and demonstrate the potential of this simple technique towards the fabrication of planar lightguide circuits in these materials.

On the linearity of holographic recording in amorphous As2S3 films

Optical recording in amorphous arsenic trisulfide was investigated for amplitude to phase conversion to be exploited in applications such as holographic recording and the fabrication of diffractive optical elements. The main result of this study is the demonstration that it is possible to obtain a linear relation between the spatial variation of the recording intensity and the recorded phase modulation. The extent of the linear recording region depends strongly on the recording wavelength. At short wavelength (458 nm in these experiments), where the rate of the photoinduced structural changes is strong, the recording is practically linear from zero exposure up to about 25% of the maximum value of the refractive index change. With higher exposure, saturation effects start to play an important role and degrade the linearity of the response. Recording with longer wavelength (488 and 514.5 nm) is less effective (absorption becomes weaker) and then relaxation processes in the material become significant. If the competition between photoinduced processes and relaxation processes is strong, the linear relationship between exposure and refractive index change can no longer be linear. Nevertheless, even for recording with the longer wavelengths, a region of exposures can be found within which variations of intensity can be converted into variations of phase with a linear relationship.

Linear holographic recording at 514 nm in amorhpous As2S3

It is shown that the linear recording of holographic gratings can be obtained at 514 nm in the amorphous arsenic trisulfide films. While strong nonlinearity was observed during recording at room temperature, these effects were eliminated when the recording was performed at temperatures below 275 K. To verify the linearity of the recording, the first- and second-order diffraction of a recorded grating were monitored during exposure. Since temperature appeared to be an important factor in obtaining the linearity of the recording, the experimental results support our qualitative model in which photoinduced structural changes, the main recording process, are deteriorated by a competitive relaxation process.