A front end system with spatiotemporal smoothing based on the use of multimode optical fibre has been developed on the Luch laser. The system consists of a broadband master oscillator, a smoothing fibre, preamplifiers, and subsystems for the formation of temporal and spatial radiation profile. The processes of generation of partially coherent radiation, its amplification and conversion into the second harmonic are experimentally investigated. At the amplifying channel output, the pulse energy of the first harmonic reaches up to 1200 J with a pulse duration of 4 ns; the technical coefficient of radiation conversion to the second harmonic is up to 44%, and the beam divergence is 0.2 – 0.25 mrad. When using smoothed radiation, the speckled structure in the far field is almost completely eliminated: the small-scale inhomogeneity of the target irradiation, integrated over the pulse time, is reduced by 1 – 2 orders of magnitude compared to unsmoothed radiation.

A new version of the method for spatiotemporal smoothing of laser radiation using spectral dispersion is proposed, which does not require the use of high-frequency phase modulators, i.e. a method based on the use of a broadband master oscillator. An experimental study of this method has been conducted on the Luch laser facility.

We present the results of our experiments at the Luch laser facility in which the processes of the destruction of iron asteroids and cometary nuclei in space by nuclear explosions on their surface are simulated based on the principle of physical similarity. We present the results of our numerical simulations of impacts on the surface of iron objects confirming the similarity of the key processes in the full-scale and model cases. The technologies of fabricating miniature mockups with parameters close to those of iron asteroids and cometary nuclei are described. For various mini-mockups 3–12 mm in size at a laser energy from 50 to 450 J we provide an experimental estimate of the energy threshold for the undeniable destruction of mockups and investigate the parameters of their fragmentation. Conclusions about the probable results of the impact of a nuclear explosion on hazardous cosmic objects have been drawn.

The presence of flaws such as bubbles, stria, and scratches in glass degrades the optical strength of components and leads to intense light scattering, loss of radiation energy, and the appearance of amplitude and phase laser beam distortions, leading to the development of intensity oscillations. The system presented here for searching for defects in optical components operates in a semi-automatic mode and allows us to find various defects and determine their coordinates and dimensions. The characteristics of the system are as follows: the minimum size of a detectable defect is 30 mu m, the absolute error in determining its coordinates is 200 mu m, and the maximum error in measuring the size is 10%. In the process of certification of optical components, Schlieren or end illumination methods are used, and their combination is used in some cases. (C) 2019 Optical Society of America

We present the results of preliminary experiments at laser facilities in which the processes of the undeniable destruction of stony asteroids (chondrites) in space by nuclear explosions on the asteroid surface are simulated based on the principle of physical similarity. We present the results of comparative gasdynamic computations of a model nuclear explosion on the surface of a large asteroid and computations of the impact of a laser pulse on a miniature asteroid simulator confirming the similarity of the key processes in the fullscale and model cases. The technology of fabricating miniature mockups with mechanical properties close to those of stony asteroids is described. For mini-mockups 4–10 mm in size differing by the shape and impact conditions, we have made an experimental estimate of the energy threshold for the undeniable destruction of a mockup and investigated the parameters of its fragmentation at a laser energy up to 500 J. The results obtained confirm the possibility of an experimental determination of the criteria for the destruction of asteroids of various types by a nuclear explosion in laser experiments. We show that the undeniable destruction of a large asteroid is possible at attainable nuclear explosion energies on its surface.

The amplifier elements upgrade at the “Luch” laser facility was carried out. Measurements showed that the upgrade of the amplifier elements resulted in the amplifier's small signal gain coefficient K0 increase from 12.9% to 14.3% depending on the capacitor charging voltage; the linear gain coefficient increase was about g0 ≈ (6-8)%. Full-scale laser experiments at the facility showed the power amplifier gain coefficient increase consistent with active medium gain coefficient measurement results.

Toothed apodizing stops fabricated by laser cutting of the volume or surface of a transparent dielectric plate that possesses a radiation strength of up to 22 J/cm(2) have been developed and investigated. It is shown that picosecond laser pulses can be used to shape teeth to within an 8-mu m accuracy on K8 glass plates with one-sided or two-sided antireflection coatings. The shaping of the spatial beam profile by toothed stops in an apodizing system has been investigated. (C) 2016 Optical Society of America.

A filter that shapes a laser beam to achieve a specified spatial intensity profile along a single coordinate is developed and studied. The filter consists of a diffractive element fabricated by laser-etching the surface of a transparent dielectric plate and a spatial angle selector. The diffractive element has a radiation damage threshold of 6 J/cm(2) at pulse width 3 ns. A three-dimensional intensity profile in the form of a parabola extending along one coordinate was experimentally produced; this intensity profile is used to compensate for spatial distortion of the beam in the main gain beamline of high-power neodymium laser systems. (C) 2016 Optical Society of America.

A system for one-dimensional spatial profiling of a laser beam is suggested, capable of compensating for the spatial laser-beam distortions that arise due to a nonuniform gain distribution over the aperture in the amplifying channel of high-power Nd : glass lasers with wide-aperture stages on disk active elements. The principle of operation, the approach to calculation of the key element parameters, and calculation and experimental results of studying the formation of spatial profiles of the laser beam intensity at the output from the system in question are described. Possible applications of the system both in single-beam and multi-beam optical schemes are considered.

A calculational and experimental study has been carried out for the spatial intensity profiles of laser beams formed at the output of an aperture-partitioning system using serrated apodizing stops with various types of serrated structures. Arrays of 2×2 and 1×2 beams with square and rectangular apertures are obtained, and it is experimentally shown that apodized beams can be formed with a high fill factor and an excess of the peak energy density relative to the mean value of no more than 1%.

The formation of the spatial intensity profile of a laser beam in a system consisting of a square serrated aperture stop and a spatial filter has been studied. This paper discusses how various shapes of the serrations of the stop, as well as various radiation-selection angles in the spatial filter, affect the resulting beam profile. The far fields of the beams formed by the serrated stops are analyzed. Special attention is paid to the question of maintaining the spatial structure of apodized beams when they freely propagate in space.

A PS-1/S1 picosecond image-tube streak camera (ITSC) with slit scan (streak camera), developed and manufactured at the General Physics Institute RAS, has been used to measure the spatiotemporal characteristics of ultrashort laser pulses generated by a petawatt-power laser installation ‘FEMTO’ at the Institute of Laser Physics Research in Sarov. It is found that such a camera is suitable for measuring the spatial and temporal parameters of single laser pulses with an accuracy of about one picosecond. It is shown that the intensity time profile of a train of picosecond pulses may be precisely defined for the pulses separated in time by a few picoseconds. The camera allows the contrast of radiation to be determined with a high (no less than ) accuracy; spatial distribution of the laser pulses can be measured with an accuracy of tens of microns, and the temporal separation of single laser pulses can be identified with an accuracy of .

We present experimental results on thermodynamic properties of dense copper plasma in Mbar pressure range. The laser facility “Luch” with laser intensity 1014 W/cm2 is used to compress copper up to ∼8 Mbar by a strong shock wave; subsequent expansion of copper plasma into Al, Ti, Sn allows us to obtain release isentropes of copper by the impedance–matching method. A theoretical analysis and quantum simulations show that in our experiments strongly coupled quantum plasma is generated.

The formation of nonlinear holographic images in a system of periodically located nonlinear mediums is studied. Analytical expressions which describe the magnitudes and locations of intensity maximums depending on the corresponding image number are derived. Comparison with numerical calculation results is presented.

We present results of experimental research carried out with the help of an acousto-optical light dispersive delay line (LDDL) on spectral correction of chirped laser pulses in a Nd-doped phosphate glass regenerative amplifier (RA) characterized by high gain (G approximate to 4 x 10(7)). The spectral resolution of the LDDL was equal to 1.1 cm(-1) at a diffraction efficiency greater than 80%. The use of the LDDL made it possible to implement operating conditions of the RA under which the duration of the output chirped pulse did not shorten in comparison with the duration of the input one, which meant that the width of the spectral emission could be preserved.

An adaptive system for the compensation of static and thermally induced wavefront aberrations of the amplification path of the 'Luch' laser facility is described. This system provided the reduction of the amplitude A of wavefront aberrations of high-power radiation and the standard deviation σ by a factor of ∼3: from A = 9.6 μm, σ = 2.4 μm to A = 3.2 μm, σ = 0.6 μm, which decreased the radiation divergence by half.

An efficient reflecting coating made of a MIRO foil with an oxide layer is fabricated, which enhances the reflection of radiation of pump lamps in the head of a high-power neodymium laser and allows a gain g0=5×10-2 cm-1 to be achieved.

The measuring technique is described and time-resolved measurements of the small-signal gain as a function of the pump energy in a disk amplification stage with neodymium phosphate glass active elements in the 'Luch' facility are presented. The distribution of the gain over the amplifier aperture in the horizontal plane is measured.