V. Lyubin

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.

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.

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.

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.

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.

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...

Opal photonic crystals infiltrated with chalcogenide glasses

Composite opal structures for nonlinear applications are obtained by infiltration with chalcogenide glasses As2S3 and AsSe by precipitation from solution. Analysis of spatially resolved optical spectra reveals that the glass aggregates into submillimeter areas inside the opal. These areas exhibit large shifts in the optical stop bands by up to 80 nm, and by comparison with modelling are shown to have uniform glass filling factors of opal pores up to 40%. Characterization of the domain structure of the opals prior to infiltration by large area angle-resolved spectroscopy is an important step in the analysis of the properties of the infiltrated regions.

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.