Vladimir A. Berenberg

Deformed-helix ferroelectric liquid-crystal spatial light modulator that demonstrates high diffraction efficiency and 370-line pairs/mm resolution

New liquid-crystal media and photoconductor materials are being utilized in spatial light modulators to increase their resolution, diffraction efficiency, speed, and sensitivity. A prototypical device developed for real-time holography applications has shown an 8% diffraction efficiency from a holographic grating with a spatial frequency of 370 line pairs/mm (lp/mm). At 18 lp/mm the device has demonstrated a 31% diffraction efficiency with a 600-micros hologram write time using 400-nJ/cm(2) write beams.

Phase OA LC SLMs for record of thin dynamic holographic correctors with diffraction efficiency over 50

It was found out, that in optically addressed liquid crystal spatial light modulator with the nematic liquid crystal and photoconductor, comprised by p-i-n diode on the base of amorphous hydrogenated silicon, it is possible to record the dynamic diffraction gratings with diffraction efficiency over 50%. The gratings were recorded with the use of S- effect. Possible reasons of the discovered effect are considered in the paper.

Self-asymmetrization of phase grating profile in a nematic S layer: Partially continuous model

The self-asymmetrization of dynamic phase grating profile in a model medium with properties of nematic liquid crystal, caused by the internal electric field induced in this medium, has been numerically simulated.

Large-aperture optically addressed spatial light modulator development

Presented are the results of investigations, directed onto creation of the OA LC SLM of reflective type with clear aperture diameter 100 mm for the record of holographic gratings with amplitude of up to 2π andasymmetrical fringe profile.

Dynamic correction for distortions in imaging optical systems using liquid crystal SLMs

Given are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.

Novel liquid crystal spatial light modulators for adaptive optics and image processing

We have developed laboratory prototypes of nematic and ferroelectric liquid crystal optically addressed spatial light modulators with photosensitive layers based on ZnSe, alpha-SiH, pin alpha-SiH, alpha-SiCH, and pin alpha-SiCH. The SLM performance characteristics measured using standard projection and holographic techniques are presented. The advantages and shortcoming of different SLM design versions are analyzed for the use in the wavefront correction and dynamic hologram recording systems. The examples are given for specific implementation of the SLMs in these systems.

Physical mechanisms of laser-induced shockwave lithotripsy in the microsecond range of laser pulse durations

Analysis of possible ways for organic minerals destruction by laser-induced shockwave is presented. Physical mechanisms describing lithotripsy with microsecond laser pulses are discussed. Theoretical considerations show that the most probable fragmentation mechanisms are connected with the existence of absorptive inclusions in the stone volume. We have shown that surface plasma flash may be considered as attendant phenomenon which does not necessarily play an important fragmentation role under our conditions of observation.

Phase reflective OA LC SLM with the clear aperture up to 50-mm for recording dynamic holographic grating with high-diffraction efficiency

The results of experimental and theoretical studies are presented on the development of optically addressed liquid crystal spatial light modulators (OA LC SLM) with clear aperture up to 50 mm and phase modulation depth up more than 2π. The optimization of electrical and optical characteristics of liquid crystal, photoconductor, dielectric mirror and blocking layers resulted in fabrication of samples of OA LC SLM that allowed writing diffraction gratings with the phase amplitude up to 2π and variable profile of grating fringes.

OA LC SLM with high-net optical efficiency for holographic correction of distortions

The reflective type optically addressed spatial light modulators (OASLMs) with an amorphous hydrogenated carbon (a- C:H) light-blocking layer (LBL) sandwiched between an intrinsic hydrogenated silicon carbide (a-Si:C:H) photoconductor and broad-band and narrow-band dielectric mirrors have been developed. FLC was used as a light modulating medium. The DHF effect in an FLC with tilt angle (Theta) equals 39 degrees and SS (Clark-Lagerwall) effect with angle 22,5 degree(s) were employed. The study showed that a flexible design of the OASLMs are possible. As a result of optimal design of the reflective type OASLMs with the dielectric mirrors of two types, the following performance characteristics have been obtained. Diffraction efficiency (DE) was about 30%, net diffraction efficiency (NE) was about 20% (spatial frequency equal 30 lp/mm and frame refreshment rate equal 200 Hz). This net diffraction efficiency practically does not depend on the direction of the reading- out light polarization for the OASLMs operating on the DHF mode.

Holographic correction in mid-IR using OA LC SLM elements

Paper presents the results of experimental demonstration of dynamic holographic correction in mid-IR, using optically addressed liquid crystal spatial light modulators and method of two-wavelength holography, when the hologram is recorded at one wavelength and reconstructed at some shifted wavelength. On such a basis one can realize the dynamic interferometer, providing the arbitrary scaling of the wave front distortions and thus to record the dynamic hologram on the differential wavelength, which can be used for dynamic holographic correction of distortions in mid-IR. Method feasibility was confirmed in experiment.