M. Klebanov

Chalcogenide glass-based three-dimensional photonic crystals

AsSeTe chalcogenide glasses are materials that are photosensitive and have a large refractive index. These properties make these glasses particularly suitable for the fabrication of photonic crystals. We present a way to build three-dimensional photonic structures from chalcogenide glasses using vapor deposition and direct holographic writing. We show that this technique is intrinsically self-aligned, providing a simple way to build layer-by-layer photonic crystals and a four-layer structure demonstrating the principle of the technique.

Three-dimensional simple cubic woodpile photonic crystals made from chalcogenide glasses

Construction of three-dimensional photonic crystals for optical wavelengths presents many technological and material science challenges. The submicron-feature-size sculpturing must be performed in high-refractive-index materials. We present the fabrication and optical characterization of ∼750 nm feature-size simple cubic woodpile photonic crystals from As2S3 (n≈2.2). The process is based on interference lithography and the layer-by-layer construction.

POLARIZATION-DEPENDENT, LASER-INDUCED ANISOTROPIC PHOTOCRYSTALLIZATION OF SOME AMORPHOUS CHALCOGENIDE FILMS

We report the observation of the influence of light polarization on the photocrystallization process and on the properties of crystallized films. Irradiation with linearly polarized He–Ne laser light results in the preparation of polycrystalline films with strong optical anisotropy (dichroism), the sign of which is determined by the direction of the electrical vector of light. The results obtained allow one to select from previously proposed mechanisms of photocrystallization. Large values of photoinduced dichroism in the films studied can be interesting for different applications of photoinduced anisotropy.

Nonlinear optical effects in chalcogenide photoresists

Both the “after-pulse effect” and the dynamic characteristics of photostructural transformations induced in glassy As0.5Se0.5 films by pulsed 532 nm excitation have been studied. The after-pulse effect investigation demonstrated more than a 103 times increase of the photosensitivity in case of pulsed excitation. Dynamic characteristics showed a dual time scale behavior and different intensity dependence of transient and long time scale signals. The obtained data indicate that the strong increase of photosensitivity following short intense pulsed light excitation is due to a two-photon effect that aids the process of structural rearrangement.

Fabrication and testing of microlens arrays for the IR based on chalcogenide glassy resists

Abstract A new technique of microlens fabrication using inorganic chalcogenide photoresists is presented. High refractive index that is characteristic of chalcogenide photoresist films and correspondingly, the optical power of the microlenses, can be increased by means of silver photodoping of the ready-made microlens array. Unique properties of chalcogenide photoresists create new possibilities for the development of microoptical components for the IR. Microlens arrays on the base of AsS and AsSe photoresists were fabricated and tested.

Photoinduced phenomena in nano-dimensional glassy As 2 S 3 films

Photoinduced anisotropy in nano-dimensional (ND) thin films ( 1µm). ND As2S3 films are shown to function also as efficient photoresists. Preliminary model based on two exponential rate processes involving defects generation and stabilization is proposed explaining the main features of the photoinduced phenomena. These observations widen the range of applications of chalcogenide glassy films such as for higher capacity of optical data storage and for the photoalignment of liquid crystals.

Permanent photoalignment of liquid crystals on nanostructured chalcogenide glassy thin films

Photoalignment of nematic liquid crystals is obtained on the chalcogenide glassy thin film of As2S3 using irradiation with polarized blue light. A uniform homogeneously aligned device is obtained with high contrast and strong anchoring. The device alignment quality is permanent as checked by following its functionality over a period of few months. The origin of the observed photoalignment is attributed to the photoinduced anisotropy in chalcogenide glasses. No differences between the different As2S3 film thicknesses observed, thus supporting the proposition that some orientational order is photoinduced on the surface of the glass and responsible for the photoalignment.

Photoinduced diffusion of Zn in chalcogenide glassy films

Abstract Thermo- and photodoping of glassy As 2 S 3 , As 2 Se 3 and As 50 Se 50 films with Zn is investigated. Existence of photo- and thermoinduced diffusion of Zn into chalcogenide films is clearly shown. Zn-dissolution and Zn-diffusion processes were studied separately. A large difference was demonstrated for the photoinduced processes in structures fabricated by evaporation of Zn under and over the chalcogenide film. The processes at the photodoped – non-doped interface were shown to determine the rate of the whole photodoping effect. Some peculiarities of the lateral Zn-photodiffusion are demonstrated. Structure and some properties of the Zn-photodoped films are studied.

Chemically deposited PbS thin film photo-conducting layers for optically addressed spatial light modulators

Lead sulfide semiconducting thin films were chemically deposited on indium tin oxide coated glass plates for use as photoreceptor layers in conjugation with optically addressed spatial light modulators (OASLMs). Deposition conditions such as temperature, reagent concentration, pH and deposition time were optimized in order to achieve homogeneous, continuous and adherent films. Mirror-like films with tunable particle size and film thickness were obtained. The microstructure and morphology evolution of the films were investigated using X-ray diffraction, scanning electron microscopy and atomic force microscopy. Electrical and optical properties were studied using four-point probe measurements, FTIR spectroscopy, photoluminescence spectroscopy, photo-current and photo-voltage measurements. Blue shift of the band gap to the short wavelength infra-red (SWIR) range was obtained as a function of particle size, and significant photovoltaic effect was measured. The resistivity of the films, as well as their photo-voltage response, were enhanced after thermal annealing. These results indicate that PbS films can serve as effective photoreceptors in OASLMs for applications including SWIR detection for night vision purposes.

Photoalignment of Liquid Crystals on Chalcogenide Glassy Films

First observation of photoaligning of nematic liquid crystals (LC) on inorganic films, namely on a chalcogenide glassy films is reported. We found that irradiation of chalcogenide surfaces by visible laser beam of low-power (∼ 30 mW) results in efficient reorientation of the director in the irradiated areas. The anchoring energy associated with the light-induced easy orientation axis is of the order 10−6 J ∗ m−2 that is typical for standard organic polymer photoaligning materials. The surprise is that the direction of the reorientation depended on the time of the exposure. For short exposures director reoriented toward the polarization of light and longer exposures resulted in the reorientation away from the light polarization. The effect of light-induced alignment was used for recording of the surface-mediated electrically controlled holograms in the LC cell.