Tigran Galstian

Fabrication and characterization of integrated optical waveguides in sulfide chalcogenide glasses

This paper reports on the fabrication process of As-S-(Se)-based chalcogenide glass optical waveguides using three techniques: photolithography, laser beam writing, and ion implantation. The fabrication method of the bulk sulfide glasses and the processing of integrated devices are described and assessed in light of the propagation characteristics and optical losses in each case.

Polymer-stabilized liquid crystal for tunable microlens applications

We investigate the electro-optical properties of polymer stabilized nematic liquid crystals produced by in situ photopolymerization technique using Gaussian laser beam. The distribution of refractive index in such structure under the action of a homogeneous electric field reveals a non-homogeneous lens-like character, approximately reproducing the intensity transverse distribution in the photopolymerizing beam.

Optical polarization grating induced liquid crystal micro-structure using azo-dye command layer

We create planar-periodic alignment in nematic liquid crystal (LC) cell by using a command layer of azo-dye molecules directly deposited on the cell substrates and exposed with two interfering laser beams of opposite circular polarizations. Permanent high efficiency polarization gratings are thus created. The diffraction efficiency of those gratings is controlled by a uniform electric field applied across the cell. The electro-optical properties of such polarization gratings are studied. Obtained gratings can be used for electrically controlled discrimination and detection of polarized components of light.

Electrically tunable polymer stabilized liquid-crystal lens

A tunable focal lens using flat electro-optical liquid-crystal cell with uniform pixel-free electrodes is developed. The lenslike gradient refractive index profile is created in the cell via the spatially distributed polymer network obtained by photopolymerization using a spatially nonuniform laser beam. The conditions of the polymer network generation are optimized to improve the optical quality of the lens and its focusing properties. Low optical loss (scattering) is achieved for a focal length smoothly tunable from infinity to 0.8m. Obtained results can be applied to develop lenses that have no moving parts and allow the electro-optical zooming.

Photochromic behavior of spiropyran in polymer matrices

The photoexcitation, relaxation, and optical erasure regimes of spiropyran- (SP-) doped polymer films were studied. Cellulose acetate, poly(vinyl acetate), and poly(methyl methacrylate) (PMMA) were used as host polymer matrices. We studied the character of the photoreaction for both coloring and bleaching processes. Reversible holographic recording in SP-PMMA films and the origin of the photochemical fatigue was studied upon repeated UV-visible irradiation cycles.

Bulk-film structural differences of chalcogenide glasses probed in situ by near-infrared waveguide Raman spectroscopy

Abstract Thin film devices based on chalcogenide glasses (ChGs) are attractive for integrated optics applications due to their good infrared transmission and high nonlinear Kerr effects. To reveal structural variations which impact physical properties depending on material processing and in-use laser conditions we employ waveguide Raman spectroscopy (WRS) in ChG thin films and fibers using excitation in the near-infrared (NIR). The Raman spectra reveal significant microstructural differences between fibers drawn from bulk As 2 S 3 glasses and unannealed films in that the latter contain As 4 S 4 molecular subunits. The high signal-to-noise ratio and the absence of undesired photoreactions make NIR WRS a versatile new approach to in situ characterization of infrared waveguide devices.

The Motility of Bacteria in an Anisotropic Liquid Environment

Although the influence on bacterial motility of many genetic and biochemical factors has been extensively studied, there have been limited studies of the impact of physical parameters. Indeed, despite the fact that natural environments are often asymmetric (such as stretched supramolecular structures), the majority of behavioral experiments with bacteria have been done in isotropic liquid solutions. In the present work, we show that the behavior of living microorganisms is dramatically different in media that are asymmetric. The example of Escherichia coli bacteria swimming in a bulk uniaxial liquid environment is used to demonstrate this phenomenon. The results of our study provide insight into the behavior of bacteria in conditions encountered in real environments and open new avenues for the control of their movements.

Recording of polarization holograms in photodarkened amorphous chalcogenide films

Polarization gratings were recorded in amorphous As2S3 chalcogenide thin films in three orthogonal recording configurations. The analysis of polarization discrimination properties of such vector gratings revealed a poor performance. It was shown that the main reason for this is the presence of nondesired scalar modulation of the same period. An exception is (s+p) recording configuration, where a pure polarization grating may be obtained even for relatively high photoexposures.

Mechanical properties of UV-waterborne varnishes reinforced by cellulose nanocrystals

There are many instances in the literature of nanocellulose-thermoplastic composites, but there are few studies on coatings reinforced by cellulose nanocrystals (CNCs). The overall objective of this research was to develop organic nanoparticles-reinforced UV-water-based coatings for wood applications and to study the effect, mainly on wear properties, of the final composite coatings. CNC was mixed in the varnishes to improve the mechanical properties of the coatings. One of the key aspects in the technology of nanocomposites remains the dispersion of the nanoparticles within the matrix as well as its affinity with the matrix. To quantify the dispersion, efficient methods of characterization are needed in order to reveal the nanosized particles. In this article, a novel characterization method based on atomic force microscopy was employed to characterize such nanocomposite coatings, by measuring surface nanoroughness, which is clearly correlated with quality of dispersion and mechanical properties. CNC was modified by either alkyl quaternary ammonium bromides or acryloyl chloride. The mechanical properties (abrasion and scratch resistances, hardness and adhesion) were analyzed and compared to the reference varnish without nanoparticles. The modified CNC addition in UV-water-based coatings results in an approximately 30–40% increase in wear resistance (abrasion and scratch), without any loss of appearance.

Spectral broadening of femtosecond pulses in a single-mode As-S glass fiber.

We report a strong spectral broadening of femtosecond pulses propagating in a single-mode As-S glass fiber of 1.5 m length. The pump pulse spectrum is broadened by a factor of five when the input power is grown up to 16.4 mW. The broadened spectra are nearly symmetric and self-phase modulation is believed to be the dominant nonlinear effect responsible for this process.