Alexander V. Parfenov

Photomodification of polymer films: azobenzene-containing polyurethanes

New results are presented on optical recording to the films of polymers substituted with azo dyes. Holographic gratings are formed in the polyurethane films by exposure to laser light without any post-treatment as in previous works using polyacrylates, epoxy-based polymers and polyesters substituted with azo dyes. It is shown for the first time that the principal mechanism of optical recording could be the mass transfer of polymers during the cis-trans isomerization of azo dye units on the polymers from illuminated areas to non-illuminated areas. Besides this transport, some irreversible photochemical reactions involving atmospheric oxygen are suggested as another possible origin for the holographic recording.

Photoinduced alignment of nematic liquid crystal on the polymer surface microrelief

A polymer film surface modified by laser illumination was used as a command surface for nematic liquid crystal (LC). Azobenzene-containing polyurethanes were taken for the material of the film. A relief grating inscribed by laser illumination onto the surface of these polymers induced a reorientation of the LC director from the initial homeotropic alignment. Possible applications of the described processes include command-surface creation for liquid-crystal displays, reversible and adaptable liquid-crystal structures for laser-beam targeting and aiming, etc.

Nonlinear image self-filtering with liquid crystal spatial light modulator

Nonlinear spatial filtering is realized due to the electro-optical effect in spatial light modulators (SLMs). Optical methods with nonlinear filtering are suggested for various optical applications such as optical inspection of photolithography masks, wavefront sensor, etc. A fast optical response of the SLM allows optical inspection with a video (or faster) rate. The optical system proposed is tolerant to the vibrations and temperature variations because of the dynamic properties of the SLM.

Advanced optical schemes with liquid crystal image converters for display applications

A few optical schemes are considered and discussed for display devices, based on liquid crystal image converters. These schemes promise enhancement in light output and diminishing in system sizes in comparison to well-known ones realized yet.

Photoinduced Alignment of Nematic Liquid Crystal on the Polymer Surface Microrelief

Abstract Polymer film surface modified in the holographic process under the laser illumination was used for nematic liquid crystal (LC) alignment. Azobenzene - containing polyurethanes were taken for a material of the film. A relief grating inscribed by laser illumination onto the surface of these polymers induced a reorientation of LC director from initial homeotropic alignment. Possible applications of described processes include command-surface creation for liquid crystal displays, reversible and adaptable in real-time liquid crystal structures for laser beam targeting and aiming, etc.

Efficient hybrid electric and thermal energy generation

We demonstrate a novel hybrid solar photovoltaic electrical and thermal energy cogeneration system with high efficiency, at potentially reduced overall weight and size compared with current solar energy systems. The new system is based on highly efficient photovoltaic solar cells and tubular water thermal receivers, incorporating holographic spectral beam light guide concentrators resulting in a more cost-effective solution. Details of fabrication and preliminary experimental testing results are presented.

Advances in ferroelectric liquid crystals for high-speed spatial-light modulators

The developed principles of optimization of the molecular structure and the mixture composition of smectic C* ferroelectric liquid crystal (FLC) are discussed, which significantly allow us to increase the speed of the electro-optic response in planar alignment of FLS. The achieved results reveal opportunity of construction of fast spatial light modulators with multiplexing owing to bistability with the time of electrical addressing about 1 microsecond(s) .

LC-tuned Fourier transform imaging spectrometer

We demonstrate a novel spectral imaging device based on an imaging Fourier transform spectrometer (FTS) with phase delays electro-optically controlled by fast tuning liquid crystal (LC) elements. The electro-optic (EO) tunable multispectral/hyperspectral imaging give the spectral imager significant advantages, including reduction in size and mass for simultaneous 2D spectral imaging, with a high spatial and spectral resolution. The technology is made very attractive for its potential military, medical and remote sensing applications where hyperspectral imaging plays a significant role in detection.

A new approach to wideband scene projection

Advances in the development of imaging sensors depend upon (among other things) the testing capabilities of research laboratories. Sensors and sensor suites need to be rigorously tested under laboratory and field conditions before being put to use. Real-time dynamic simulation of real targets is a key component of such testing, as actual full-scale tests with real targets are extremely expensive and time consuming and are not suitable for early stages of development. Dynamic projectors simulate tactical images and scenes. Several technologies exist for projecting IR and visible scenes to simulate tactical battlefield patterns - large format resistor arrays, liquid crystal light valves, Eidophor type projecting systems, and micromirror arrays, for example. These technologies are slow, or are restricted either in the modulator array size or in spectral bandwidth. In addition, many operate only in specific bandwidth regions. Physical Optics Corporation is developing an alternative to current scene projectors. This projector is designed to operate over the visible, near-IR, MWIR, and LWIR spectra simultaneously, from 300 nm to 20 μm. The resolution is 2 megapixels, and the designed frame rate is 120 Hz (40 Hz in color). To ensure high-resolution visible imagery and pixel-to-pixel apparent temperature difference of 100°C, the contrast between adjacent pixels is >100:1 in the visible to near-IR, MWIR, and LWIR. This scene projector is designed to produce a flickerless analog signal, suitable for staring and scanning arrays, and to be capable of operation in a hardware-in-the-loop test system. Tests performed on an initial prototype demonstrated contrast of 250:1 in the visible with non-optimized hardware.

Nanoparticle-doped isotropic liquid crystals

We demonstrate a new material composed of isotropic liquid crystal (ILC) blended with semiconductor nanoparticles, which could result in a novel high-speed, multiple-notch broadband passive optical switch to selectively discriminate bands of electromagnetic radiation in intelligence, surveillance, or reconnaissance systems. The new material has been demonstrated high nonlinear 3rd order optical Kerr coefficients (light-induced refractive index change, n2) exceeding 100 times of classic nonlinear material CS2 with n2 = 1.2E-11 esu. Details of fabrication and experimental results are presented.