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Dye-doped nematic liquid-crystalline polymers exhibit much higher orientational optical response than the systems based on low-molar-mass liquid crystals. In addition, polymer materials possess the glassy state, which allows one to record their supramolecular structure. We study the effect of light field inhomogeneity on the director deformation in the geometry of Freedericksz transition and recording of corresponding phase structures. The relationship of the light beam width with the threshold light intensity and the size of the induced and recorded deformation region was determined. An influence of the beam waist radius on the polymer director relaxation time was detected. The results of numerical calculations based on the continuum theory and the independence of the enhancement factor of the optical torque on light–polymer interaction geometry agree with the experimental data.

A comparative study of optical orientation in nematic liquid crystals (NLCs) doped with a low-molar-mass bis-azobenzene dye (monomer) and a comb-shaped polymer with side fragments similar in structure to the monomer has been carried out. Both types of bis-azobenzene dopants induced a sign-alternating nonlinearity in the NLC: the positive when the angle Ψ between the light field and the director is less than a certain critical value Ψc and the negative in the opposite case of Ψc The magnitudes of the optical-torque enhancement factors due to trans- and cis-isomers (ηT and ηC), and the ratios ηT/ηC for the low- and high-molar-mass dopants are compared. The results obtained show the possibilities of increasing the orientational optical nonlinearity when passing from low-molar bis-azobenzene dye dopants to the corresponding polymers and are important for elucidating the optimal architecture of absorbing additives.

Dye-doped nematic side-chain liquid-crystalline polymers possess extraordinary large optical nonlinearity and ability to store the induced orientational deformations in a glassy state, which makes them a very promising material for photonic applications. In this study, the phase structures were generated and recorded in the bulk of a 50-&mu, m layer of a nematic liquid-crystalline side-chain polymer, containing polyacrylate backbone, spacer having five methylene groups, and phenyl benzoate mesogenic fragment. The polymer was doped with KD-1 azodye. The director field deformations induced by the light beam close to the TEM01 mode were studied for different geometries of light&ndash, polymer interaction. The phase modulation depth of 2&pi, was obtained for the 18-&mu, m spacing between intensity peaks. The experimental data were analyzed based on the elastic continuum theory of nematics. The possibility to induce and record positive and negative microlenses in the polymer bulk was shown experimentally.

The nature of crystallization in telluride based phase change memory materials is being actively discussed, and we present new experimental results on the effect of a pulsed laser treatment on the amorphous thin film crystallization of composition Ge2Sb2Te5 (GST225). It is shown that there are two ways of crystalline phase formation under femtosecond pulses excitation. At the moderate value of laser fluence, crystalline fraction forms inside the solid amorphous phase. This process is apparently two-stage, and this leads to formation of fine-grained polycrystalline material. The second way of crystallization proceeds at higher levels of the laser fluence, closer to the beam axis. In this case, larger grains are produced closer to the beam axis, and eventually no new nuclei can be formed due to high cooling velocity leading to inhibition of nucleation. The article also presents the results on the effect of the substrate type (metallic or oxide) and film thickness on crystallization, which is due to the light penetration depth and reflection from the film-substrate interface.

We report the first direct laser-writing of buried channel waveguides in ZnS. A depressed cladding waveguide with propagation loss of 0.62 dB/cm at 1030 nm allowed to obtain spectral broadening under femtosecond-pumping at 1030 nm. © 2018 The Author(s). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited.

A large mode area depressed cladding waveguide was inscribed by a femtosecond laser beam in bulk of high purity 70TeO2-22WO3-8Bi2O3 glass. Non-linear propagation of femtosecond pulses in the single mode waveguide with mode field diameter of 12 μm was investigated under input at 1030 nm wavelength. The highest peak value of a Raman-gain coefficient of all the tellurite glasses was measured (1.2x10−9 cm/W). The dispersion of the refractive index was obtained in the range of 1170-2300 nm. Spectrum broadening of up to 160 nm at the −10 dB level was observed under input pulse energy as low as 84 nJ in a 14 mm long waveguide. The spectrum broadening was numerically simulated, and it was found that both the Kerr and the Raman nonlinearities result to comparable contributions to the spectrum transformation.