Grating compressor optimization aiming at maximum focal intensity of femtosecond laser pulses.

It is shown that the optimal geometry of a Treacy compressor is the full-aperture compressor, in which the beam size at the first diffraction grating is equal to its length. Despite the energy losses and greater size of the focal spot, such a compressor provides considerably higher (by 1.5-2 times) focal intensity than an energy lossless compressor.

Pulse fluence noise dynamics at free-space propagation.

The dynamics of fluence noise of an optical pulse at free-space (e.g., vacuum) propagation has been studied.

Small-scale fluctuations of laser beam fluence at the large B-integral in ultra-high intensity lasers.

Analytical expressions for the spatial spectrum of fluence fluctuations of a laser pulse propagating in a medium with Kerr nonlinearity have been obtained. It is shown that inhomogeneities with a spatial scale much larger than the critical scale of self-focusing grow insignificantly even at large values of the B-integral. Experiments using BK7 glass and a KDP crystal as a nonlinear medium confirm the obtained theoretical results.

Improving focusability of post-compressed PW laser pulses using a deformable mirror.

The use of the post-compression technique ensures gain in laser pulse peak power but at the same time degrades beam focusability due to the nonlinear wavefront distortions caused by a spatially nonuniform beam profile. In this paper a substantial focusability improvement of a post-compressed laser pulse by means of adaptive optics was demonstrated experimentally. The Strehl ratio increase from 0.

Enhancing the temporal contrast and peak power of femtosecond laser pulses.

It is shown that a nonlinear polarization interferometer and a chirped mirror enable enhancement of the contrast of high-power laser pulses with a duration of tens and hundreds of femtoseconds by several orders of magnitude and simultaneously a several-fold reduction of their duration. Different variants of interferometers based on cubic nonlinearity in KDP and DKDP crystals are considered. The interferometer and chirped mirror parameters are optimized aimed at enhancing the peak power of the compressed pulse.

Thermally induced depolarization in a silicon (c-Si) single crystal.

Single-crystal silicon is one of the most promising materials for producing test masses for the new generation of laser interferometers intended for the detection of gravitational waves. We studied the thermally induced depolarization of radiation in single-crystal silicon with [001] orientation at a wavelength of 1940 nm at room temperature. The value of the piezo-optical anisotropy ratio was found to be ξ = -0.

11 fs, 1.5 PW laser with nonlinear pulse compression.

The PEARL laser output pulse with a duration of 60-70 fs was compressed to 11 fs after passing through a 5-mm thick silica plate and reflecting from two chirping mirrors with a total dispersion of -250 fs. The experiments were carried out for the B-integral values up to 19 without damage of the optical elements, which indicates that small-scale self-focusing was suppressed. The results obtained show the possibility of further nonlinear compression scaling to multipetawatt power in pulses with duration commensurate with the field period.

Nonlinear polarization interferometer for enhancement of laser pulse contrast and power.

A method for enhancing the temporal contrast of high-power femtosecond laser pulses is proposed. The suppression of low-intensity radiation and the simultaneous 100% transmission of a pulse peak are attained due to the nonlinear phase difference π between the orthogonally polarized waves, leading to a 90-degree rotation of polarization. The polarization interferometer has an in-line geometry that does not demand spatial beam separation.

Single-shot laser pulse reconstruction based on self-phase modulated spectra measurements.

We report a method for ultrashort pulse reconstruction based only on the pulse spectrum and two self-phase modulated (SPM) spectra measured after pulse propagation through thin media with a Kerr nonlinearity. The advantage of this method is that it is a simple and very effective tool for characterization of complex signals. We have developed a new retrieval algorithm that was verified by reconstructing numerically generated fields, such as a complex electric field of double pulses and few-cycle pulses with noises, pedestals and dips down to zero spectral intensity, which is challenging for commonly used techniques.

Terbium gallium garnet ceramic Faraday rotator for high-power laser application.

A terbium gallium garnet (TGG) ceramic Faraday rotator (FR) with an isolation ratio of 33 dB was demonstrated at a laser radiation power of 257 W. This FR can be equipped with a large optical aperture by using ceramics technology to prevent laser damage at high-energy pulse operation. The thermal lens of a 257 W laser with a beam diameter of 2.

Self-compensation of thermally induced depolarization in CaF₂ and definite cubic single crystals.

Compensation of thermally induced depolarization in laser active elements at small birefringence without additional phase elements was proposed and observed experimentally. Requirements to the crystals were formulated. An order of magnitude reduction of depolarization degree was obtained experimentally.

Drastic reduction of thermally induced depolarization in CaF₂ crystals with [111] orientation.

The key importance of the sign of the stress-optic anisotropy ratio for reducing thermally induced depolarization in cubic crystals with 432, 4¯3m and m3m symmetry is addressed. A simple method for measuring the stress-optic anisotropy ratio (including its sign) was proposed and verified in CaF<₂ and TGG crystals by experiment. The ratio at room temperature for the wavelength 1076 nm was measured to be -0.

Thermal effects in the Input Optics of the Enhanced Laser Interferometer Gravitational-Wave Observatory interferometers.

We present the design and performance of the LIGO Input Optics subsystem as implemented for the sixth science run of the LIGO interferometers. The Initial LIGO Input Optics experienced thermal side effects when operating with 7 W input power. We designed, built, and implemented improved versions of the Input Optics for Enhanced LIGO, an incremental upgrade to the Initial LIGO interferometers, designed to run with 30 W input power.

Compensation of thermally induced depolarization in Faraday isolators for high average power lasers.

A compensation scheme for thermally induced birefringence in Faraday isolators is proposed. With the use of this scheme a 36-fold increase of the isolation degree was attained in experiment. A comparative analysis of the considered scheme and the earlier Faraday isolator schemes with high average radiation power is performed.

Reduction of thermally induced depolarization of laser radiation in [110] oriented cubic crystals.

The first measurements of thermally induced depolarization in a [110] oriented cubic crystal at powerful heat release were made. It was demonstrated that depolarization in a crystal with such orientation may be less than in analogous crystals having orientation [001] or [111]. In a TGG crystal, for example, maximum depolarization value was 10% and dropped down to 3% with a further increase of radiation power in full conformity with the theoretical predictions.

Adaptive acousto-optic technique for femtosecond laser pulse shaping.

We discuss the theoretical and experimental investigation of acousto-optic dispersive tunable filters, based on quasi-collinear geometry of light-sound interaction in a tellurium dioxide single crystal. The geometry uses the effect of strong acoustic anisotropy in the paratellurite as well as peculiarities of acoustic wave reflections at the free boundary of the crystal. A mathematical concept for determination of optical, electrical, and constructional parameters of the filters is developed.

Experimental study of thermal lens features in laser ceramics.

Thermal lens measurements were made by means of a high-accuracy phase shift interferometer that combines a lambda/1000 sensitivity and 10 microm transverse resolution. The effect of random small-scale modulation in thermally induced phase distortion predicted earlier was proved experimentally. The statistical parameters of modulation were measured depending on heating power for two different ceramic samples.

Synchronization of two Q-switched lasers with 150 ps jitter.

Two Nd:YLF lasers with a pulse duration of about 2 ns have been synchronized. The duration and synchronization of two laser pulses are provided by two pairs of Pockels cells with synchronized voltage pulses. One of the Pockels cells in the first pair ensures Q switching, and the other cuts out a 2 ns pulse from the giant 20 ns pulse.

Thermally induced birefringence in Nd:YAG ceramics.

Analytical expressions for eigenpolarizations and phase delays in grains of thermally loaded Nd:YAG ceramic rods have been derived. It is shown that the depolarization of radiation in polycrystalline ceramics results in beam modulation with a characteristic size of the order of the ceramic grain size. It is reasonable to increase the ratio of rod length to grain length both to diminish this modulation depth and to compensate for birefringence by use of known techniques.

Interferometry based technique for intensity profile measurements of far IR beams.

We present a novel, to the best of our knowledge, method for measuring the intensity profile of far-IR beams. The method is based on the measurements of nonstationary variation in optical thickness of a fused-silica plate heated by the studied radiation. The optical thickness is observed by means of a reflecting interferometer.

Comparison of phase-aberrated laser beam quality criteria.

With any form of phase distortions there is the need to qualitatively characterize beam quality. Three different qualitative criteria are most commonly used for this purpose, each of them describing the beam with one ratio: the overlapping integral, the Strehl ratio, and the M2 parameter. We have analyzed the interrelation of the above- mentioned criteria in the three most common types of beam quality degradation: thermal lens, electronic self-focusing, and spherical aberration.

High-precision methods and devices for in situ measurements of thermally induced aberrations in optical elements.

An optical system that comprises two devices for remote measurements, a broadband optical interferometer and a scanning Hartmann sensor, is described. The results of simultaneous measurements with both devices and the results of numerical modeling of sample surface heating are presented.

Thermally induced birefringence in Faraday devices made from terbium gallium garnet-polycrystalline ceramics.

We have developed a model that describes thermally induced birefringence in polycrystalline ceramics that are exposed to a magnetic field. Conditions under which traditional compensation techniques (for glass and single crystals) can be effective for ceramics have been found. It is shown that a ceramic is almost equivalent to a [111]-oriented crystal if the ratio of the rod length to the grain size is approximately 300 or more.