The current trends in the creation of high-energy repetitively pulsed continuous wave lasers with pulse energies of tens and hundreds of joules are considered. Active media are analyzed for their use in such lasers. The Yb:YAG active crystalline and ceramic elements produced in Russia are experimentally studied at temperatures from 100 to 295 K. The data of the cryogenic cooling system for active elements are presented. A diode pumping system for active elements and a homogenizer for its emission are described. The physical and technical characteristics of the pumping system are given. Fresnel losses, absorption losses, and losses due to enhanced spontaneous emission, which reduce the energy stored in the inverse population, are measured experimentally. The results of measuring the gain in multi-pass circuits with different sets of active elements are presented.

Current trends in developing high-energy lasers with pulse energies in the tens and hundreds of joules are considered. Active media are analyzed for their use in such lasers. Yb:YAG active crystalline and ceramic elements (AE) of Russian production are experimentally investigated at temperatures from 100 K to 295 K. The data of the AE cryogenic cooling system are presented. A diode pumping system for AE and a homogenizer of its radiation are described. The physical and technical characteristics of the pumping system are given. Fresnel losses, absorption losses, and losses due to amplified spontaneous emission (ASE), which reduce the energy stored in an inverted population, are experimentally measured. The results of measuring the gain in multipass circuits with different sets of AEs are presented.

Results of experiments aimed at amplification of the pressure of laser-induced shock wave on the passage from low- to high-density target material via vacuum gap are presented. During the action of nanosecond laser pulse of terawatt power on plane composite targets comprising a layer of laser radiation absorber of low-density (0.01–0.025 g/cm3) spaced by vacuum gap from a layer of aluminum, the shock-wave velocity in aluminum reached 25–29 km/s and a pressure jump at the aluminum layer boundary was 1.2–1.5 times as large as that observed in experiments on the cumulative transition of laser-induced shock wave into a solid. The obtained experimental data are compared to results of the numerical calculations performed using hydrodynamic programs in which the shock-wave generation and propagation was modeled with allowance for the interaction of laser pulses with partly homogenized plasma of the porous material. Based on the results of experiments, numerical calculations, and their theoretical analysis, the efficiency of using low-density porous media in the targets intended for their equation of state investigations and inertial confinement fusion ignition is considered.

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.

Рассмотрены методы определения коэффициентов отражения зеркальных покрытий оптических деталей, основанные на многократном отражении излучения от измеряемой поверхности и контроле величин регистрируемых сигналов, обеспечивающие абсолютную погрешность измерения <0.1%. Проведена их экспериментальная аттестация, подтвердившая высокую точность таких измерений. Ключевые слова: коэффициент отражения, мощные лазерные установки, погрешность измерения.

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

The paper presents the diagnostic system for velocity measurements of reflecting objects in high energy physics experiments. The principle of continuous velocity measurements based on the Doppler frequency shift analysis of a probe monochromatic wave reflected by the moving surface of the sample. System is designed to measure velocity in the interval of 550 km/s. Powerful laser pulses expose the target and generate shock waves inside it. The back side of target is illuminated by probe laser beam at a wavelength of 660 nm. Scattered probe light collected by a lens and injected into the optical system. Two Mach-Zehnder interferometers with different reference delay etalons form a vernier measuring system. A passive channel records luminescence in the shock wave front. Spatial resolution of the optical layout is about 3 mu m.

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.

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.

Method is explored of a focusing laser beam homogeneous quality receiving with a non-stationary plasma layer (DPPP) applying. The DPPP research is conducted on the Iskra-4 and Iskra-5 laser facilities aimed on its performance optimization. Irradiation inhomogeneity is received <8-10% at the reference time of an intensity distribution transposition -0.4 ps. It is shown, that the DPPP smoothing method raises the efficiency of radiation energy transfer to a laser target.

The spatiotemporal smoothing of the intensity distribution of a focused laser beam was investigated on the Iskra-4 laser setup using a dynamic plasma phase plate produced by vaporisation of a special target placed at the beginning of the caustic of the focused beam. It is shown that the transmittance of the plasma target in the 1013— 2 × 1014 W cm-2 intensity range is no less than 70% — 80%. The introduction of the dynamic plasma phase plate lowered the relative fluctuations of the spatial intensity distribution from 100% to ~10%. The characteristic time of the intensity distribution variation in the focal plane is 0.4 ps.

The investigations of the influence of various types of wavefront distortions, varying in time, on the intensity distribution on the surface of a target are carried out. It is shown that distortions of a wavefront, equivalent to transverse displacement in time of a beam in far field at an angle of approximately 10 diffraction angles, results in practically full smoothing of a specl-structure of intensity distribution. Creation of phase distortions of a beam assigned as running in a cross section wave with an amplitude of more than 3 radian and with a spatial size exceeding 20–30 times the size of the kinoform phase plate element, permits us to reduce the depth of modulation in distribution of intensity in far field also. The capability of application is considered as a smoothing device of the dynamic plasma layer, based on the volume-structured medium. The model of energy transport process in such media is developed. Matching of calculation and experimental results is conducted.

The results of the first experiments devised to investigate the mixing of thin layers of Al and Au during the laser acceleration of flat three-layer targets of Si (5 μ m), Al (2 μ m), and Au (0.05–0.26 μ m) by radiation converted to the second harmonic from the Iskra-4 iodine laser with an intensity of 4×10 13 −7×10 13 W/cm 2 ( τ 0.5 ∼1 ns), which acts on the Si side of the target. A method for detecting the occurrence of mixing is developed. It is established that under the experimental conditions the thickness of the mixing region is at least ∼0.15 μ m. The results of a theoretical analysis of the evolution of the disturbances leading to mixing are presented.

The requirements for the laser facility based on illumination uniformity calculations which allow the user to achieve implosion of 103 are formulated. The experimental results of the improved direct drive target illumination uniformity are presented. Using it for smoothing properties of the plasma phase plate (PPP) is proposed. PPP parameters for spatial and temporal smoothing of DDT illumination nonuniformities are evaluated.