The transformation of elliptical polarization in a layer of azobenzene-containing amorphous polymer is calculated. The dependences of the Stokes parameters for the propagation of a light wave deep into the layer are obtained. It is shown that the light-induced change in absorption leads to a decrease in the ellipticity of the light wave, which, in turn, slows down the rotation of the polarization ellipse. The obtained results are important for optical writing of phase structures in polymers.

Phase-change materials are very interesting and promising objects for various optical applications due to simple and high-speed switching between the amorphous and crystalline states. In this study, we consider the specific features of laser crystallization and ablation of thin amorphous Ge2Sb2Te5 films exposed to the HG01 (Hermite–Gaussian TEM01) mode of cw visible light. This exposure led to two-zone crystallization or ablation, depending on the laser intensity. Microscale two-zone ablation made it possible to observe Young’s fringes for the radiation transmitted through a sample, as in the case of two-point-source interference. This approach is promising for express analysis of the laser beam profile.

The formation of the modified area, which acts as phase converter for vortex generation, in the amorphous thin layer of the azo-containing polymer under the action of structured light beam is considered. The optical axes are produced in accordance with the polarization structure of the pump light beam. The beam with radial polarization induces the axially-symmetric optical axis distribution (similar to q-plate) with negative optical anisotropy proportional to the light beam intensity. We demonstrate that this light-induced modification can efficiently convert the probe Gaussian beam into optical vortex with the topological charge 2.

We report an experimental study of the self-action of TEM01 and TEM00 Gaussian modes in a layer of a comb-shaped amorphous polymer with cyanobiphenyl and azobenzene side fragments. For the linearly polarized TEM01 mode, a pattern of aberration self-action is observed in the form of rings with an additional system of the fringes, caused by interference from two intensity peaks. The position of the fringes and the microscopic image of the deformation region correspond to the local nature of the nonlinear optical response. For the circularly polarized (with an ellipticity of about 7

The effect of light beams of various structures (TEM00, TEM01, annular, vortex) on films of the photochromic azobenzene-containing polymethacrylates is studied. To analyze induced anisotropy, the methods of polarization microscopy and aberrational self-action were used. The latter is convenient non-destructive method for determining induced phase profiles and the anisotropy sign. Under the influence of the polarized light in the visible range, initially amorphous polymer samples become optically anisotropic, the induced anisotropy obeys the dose law in a wide range of light powers and illumination times. The induced anisotropy can be rewritten upon reexposure to light or erased by heating above the transition point to the isotropic state. The direction of the induced optical axis depends on the type of light polarization. By controlling the polarization and structure of a light beam, it is possible to obtain regions with a refractive index higher or lower than the original one, as well as complex distributions, including similar to those in phase converters for vortex generation. High photosensitivity in the UV and visible ranges, local response and rewritability make these materials promising for photopatterning and light-beam diagnostics.

Light-induced director field deformation of a nematic liquid crystal in the field of an obliquely incident laser beam is experimentally studied with aberrational self-action and polarization microscopy. Each of the methods has features associated with the geometry of the light interaction with the director. The combination of methods significantly expands the possibilities of reconstructing the light-induced nonlinear phase shift profile and the director field deformation.

Статья посвящена крупному ученому и организатору науки, профессору Льву Михайловичу Блинову, посвятившему свою жизнь исследованию жидких кристаллов и организованных молекулярных структур. Лев Михайлович является основателем школы экспериментальных исследований органических пленок и жидких кристаллов в Советском Союзе, им воспитаны десятки молодых ученых, ставших кандидатами и докторами наук. Л.М. Блиновым написаны сотни научных статей, множество обзоров, монографий и учебников, читались лекции как в России, так и по всему миру. Кратко изложена биография Льва Михайловича, дан обзор его наиболее значимых достижений и отдельных публикаций, получивших широкий резонанс в научном сообществе. Приведены воспоминания учеников и коллег.

An ultrashort-pulse laser inscription of embedded birefringent microelements was performed inside bulk fluorite in pre-filamentation (geometrical focusing) and filamentation regimes as a function of laser wavelength, pulsewidth and energy. The resulting elements composed of anisotropic nanolattices were characterized by retardance (Ret) and thickness (T) quantities, using polarimetric and 3D-scanning confocal photoluminescence microscopy, respectively. Both parameters exhibit a monotonous increase versus pulse energy, going over a maximum at 1-ps pulsewidth at 515 nm, but decrease versus laser pulsewidth at 1030 nm. The resulting refractive-index difference (RID) Δn = Ret/T ~ 1 × 10−3 remains almost constant versus pulse energy and slightly decreases at a higher pulsewidth, generally being higher at 515 nm. The birefringent microelements were visualized using scanning electron microscopy and chemically characterized using energy-dispersion X-ray spectroscopy, indicating the increase of calcium and the contrary decrease of fluorine inside them due to the non-ablative inscription character. Dynamic far-field optical diffraction of the inscribing ultrashort laser pulses also demonstrated the accumulative inscription character, depending on the pulse energy and the laser exposure. Our findings revealed the underlying optical and material inscription processes and demonstrated the robust longitudinal homogeneity of the inscribed birefringent microstructures and the facile scalability of their thickness-dependent retardance.

Liquid crystals are of great interest in the field of nonlinear optics due to their efficient response to low intensity light fields. Here we present a new, to the best of our knowledge, mechanism of a nonlinear optical response which is observed for a dye-doped dual-frequency nematic liquid crystal. The local increase in temperature caused by the absorption of light beam in the liquid crystal medium leads to spatial variation and inversion of the sign of the dielectric anisotropy. When an alternating current electric field with a frequency close to the cross-over frequency is applied to the liquid crystal cell, the planar orientation sustains at the beam periphery, but elastic deformation occurs in the irradiation region. In the case of a dye dopant with negative absorption dichroism, a first-order orientational transition with large bistability region is obtained.

The inscription regimes and formation mechanisms of form-birefringent microstructures inside nano-porous fused silica by tightly focused 1030- and 515-nm ultrashort laser pulses of variable energy levels and pulsewidths in the sub-filamentary regime were explored. Energy-dispersion X-ray micro-spectroscopy and 3D scanning confocal Raman micro-spectroscopy revealed the micro-tracks compacted by the multi-shot laser exposure with the nanopores hydrodynamically driven on a microscale to their periphery. Nearly homogeneous polarimetrically acquired subwavelength-scale form-birefringence (refractive index modulation ~10−3) was simultaneously produced as birefringent nanogratings inside the microtracks of wavelength-, energy- and pulsewidth-dependent lengths, enabling the scaling of their total retardance for perspective phase-modulation nanophotonic applications. The observed form-birefringence was related to the hierarchical multi-scale structure of the microtracks, envisioned by cross-sectional atomic-force microscopy and numerical modeling.

The processes of light-induced orientation at oblique incidence of a light beam on a dye-doped nematic liquid crystal (NLC) are experimentally studied with the simultaneous use of the methods of aberrational light beam self-action and polarization microscopy. Each method has features associated with the geometry of light propagation in an NLC, and their combination significantly expands the possibilities of reconstructing the light-induced profile of the nonlinear phase shift and director deformation field.

Three-segment microtracks were for the first time inscribed in bulk fluorite in the scanning mode via multishot exposure by tightly-focused 515-nm ultrashort laser pulses of variable pulse energy and pulsewidth (0.3-3.8 ps). The local micro/nanoscale material modification and related refractive-index changes within the microstructures, envisioned by optical and cross-sectional electron microscopy, result in their form birefringence acquired by polarimetric microscopy. Retardance and thickness of the microstructures were measured by optical polarimetry and confocal scanning Raman/photoluminescence microscopy, respectively, exhibiting the intensity- and pulsewidth-dependent trends, with the maximal effect for approximate to 1-ps laser pulses. These and complementary optical self-reflectance studies enabled for the first time to consider ultrafine, pulsewidth-dependent interferential longitudinal sub-structure of the birefringent microtracks. Such regular longitudinal sub-structure was proposed to emerge via back-reflection and interference of laser radiation prior near-critical laser-generated plasma in the focus, and the following transverse plasmon propagation in each nanosheet of ionized fluorite in the resulting sub-wavelength interference pattern. Our findings open the way for ultrashort-pulse laser inscription of embedded optical microstructures in non-oxygen fluoride materials and shed light onto the underlying laserdielectric interactions.

We report the light beam action on the nematic liquid crystal film with a free surface. It was found that a weak light absorption by the liquid crystal substrate dramatically changes the orienting properties of the light beam; in particular, a thermal gradient field induces an umbilical defect formation.

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 signalternating nonlinearity in the NLC: the positive when the angle Psi between the light field and the director is less than a certain critical value Psi(c) and the negative in the opposite case of Psi(c) < Psi <= 90 degrees. The transition from the monomer to polymer led to a decrease in the critical angle Psi(c), i.e., to an expansion of the region of negative nonlinearity. At the same concentration of chromophores, an increase in both negative and positive nonlinearities occurs. The magnitudes of the optical-torque enhancement factors due to trans- and cis-isomers (eta(T) and eta(C)), and the ratios eta(T)/eta(C) 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. (C) 2021 Elsevier B.V. All rights reserved.

Birefringent microstructures recorded at a fixed depth under the action of laser pulses with a wavelength of 1030 nm, different durations in the range of 0.3–3.8 ps, and different energies have been obtained for the first time in the bulk of a fluorite plate. The dependences of the retardance in microstructures for orthogonal polarizations on the energy/intensity of radiation are monotonically increasing at any directions of laser pulses. A mechanism has been proposed for the formation of birefringent microstructures at the reflection of laser pulses from the near-critical bulk plasma near the focal region with the formation of a standing electromagnetic wave in front of the plasma along the optical axis. This wave is fixed in the material in the form of arrays of nanostructures planes (nanogratings) with the orientation of grooves of local modification of the material and its refractive index perpendicular to the laser polarization. The observed sublinear increase in the retardance in birefringent microstructures with an increase in the energy/intensity of laser radiation is described within this mechanism.

The effect of nonlinear light action on a thin (∼10 µm) films of the nematic liquid crystal deposited onto the absorbing substrate is experimentally investigated. The dynamics of the orientational and thermocapillary effects is directly studied. The two types of orientational processes were found out. The first one appears for several hundreds of milliseconds when the light beam irradiation is turned on or off. The second one develops much slowly and does not relax during the light beam irradiation.

The action of ultrashort laser pulses on dielectrics leads to the processes of redistribution of the laser pulse energy in the interaction region. The mechanisms of ultrafast energy deposition and the electron dynamics under the action of ultrashort laser pulses determine the type of final structures or elements in the transparent dielectrics. One type of these elements is a birefringent nanogratings formed with an orientation perpendicular to the laser radiation. In this work, laser-induced birefringent structures in calcium fluoride (CaF2) bulk were obtained under the action of tightly-focused laser pulses with durations 0.3-3.8 ps and wavelengths of 515 and 1030 nm. Birefringence in modified region was analyzed using polarization contrast optical microscope with Abrio imaging system.

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-μm 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–polymer interaction. The phase modulation depth of 2π was obtained for the 18-μm 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.

Bulk microstructuring of silica glass was performed by one-dimensional raster-scanning of tightly focused visible-range femtosecond-laswer beam with different polarizations. Microstructures fabricated at linear and circular polarizations, demonstrated enhanced blue-range extinction without any distinct birefringence.