An approach associated with the use of active media with a non-uniform dopant ions concentration distribution is proposed to increase the pulse energy level and optimize the high power laser amplifier parameters. The optimal profiles of the laser-active ions gradient distribution in the amplifying medium were determined. A crystal sample was obtained in which the concentration of the activator changes sharply from 5 at.% to 10 at.% over a length of 3–5 mm.

This work is devoted to the method for studying temperature distribution in solid-state active elements of high average power laser amplifiers. Temperature distribution in an active element of the cryogenically-cooled diode-pumped laser amplifier with high average power were investigated and analyzed. The investigation was carried out for various pump beam diameters and repetition rates 500 and 1000 Hz.

A time-dependent model of laser amplification in an Yb:YAG crystal is developed, with accounting of active media thermophysical and laser characteristics dependencies on the temperature distribution, the dependence of the gain medium laser characteristics on the seed wavelength and the effect of amplified spontaneous emission. The numerical simulation of the laser amplification process in the active element of a multidisk amplifier was performed and compared to experimental results.

The influence of optical centers concentration profiles on thermal fields under high-power end-face diode pumping is analyzed using numerical model. It is shown that non-uniform distribution profiles of optical centers concentration are very promising for high average pump power laser amplifiers. The possibility of creating concentration profiles of optical centers in gradient-activated crystals with YAG matrix with a specified distribution along the growth axis of the crystal is demonstrated. A technology of growing gradient-activated single crystal involving active mirror as active element is proposed and discussed.

A numerical three-dimensional non-stationary model describing laser amplification process with account of the dependencies of properties of active element on temperature distribution was developed. A numerical simulation of the laser amplification process in cryogenically cooled high peak, high average power amplifier was performed and it is shown that optimization of pump parameters allows one to obtain up to 50% more energy at the output of the amplifier.

A time-dependent three-dimensional model for the laser amplification process has been constructed with allowance for the effect of the temperature distribution on the thermophysical and lasing characteristics of gain media. We have performed numerical modelling of the laser amplification process in the gain elements of a two-stage subjoule-level cryogenic laser amplifier operating at a pulse repetition rate of up to 1 kHz. It has been shown that taking into account the temperature distribution is of critical importance in calculation of cryogenically cooled laser amplifiers pumped with high-power diodes. We have found optimal diode pump parameters at which the maximum achievable pulse energy at the amplifier out-put can reach 300 and 570 mJ at pulse repetition rates of 1000 and 500 Hz, respectively.

The dynamics of phase distortions during laser amplification in the cryogenically cooled active elements with high power diode pump was modeled and analyzed. The possibility of significant reduction of wavefront distortions with small decrease of the gain coefficient by choosing the optimal values of the pump radiation radius is shown.

In this paper we focus on investigation of temperature distributions in laser elements based on Yb:YAG crystal at cryogenic temperatures. We consider the approach of using elements with non-uniform concentration distribution of dopant ions to reduce an average temperature and to minimize temperature gradients in active elements of laser amplifiers. The results of modeling are presented and discussed.

A new original method has been developed and experimentally implemented, allowing temperature fields to be contactlessly measured in the pump region of active elements in high-power-diode-pumped laser amplifiers, including those operating at cryogenic temperatures. The presence of a temperature gradient of similar to 57 K mm(-1) along the pump beam axis at the centre of the active element of the laser amplification unit operating at cryogenic temperatures with a pulse repetition rate up to 1 kHz is simulated and experimentally confirmed.

The source of instabilities in the multidisk diode-pumped high power Yb:YAG laser amplifier with cryogenic closed-loop cooling in the laser amplification channel of the high intensity laser system with 1 kHz repetition rate was determined. Dissected copper mounts were designed and used to suppress instabilities and to achieve repeatability of the system. The equilibrium temperature dependency of the active elements on average power was measured. The seed laser for the multidisk amplifier was numerically simulated and designed to allow one to increase pulses output energy after the amplifier up to 500 mJ.

Amplification experiments in the multidisk laser amplifier of all diode-pumped cryogenically cooled all solid state laser system have been carried out. The dependency of gain coefficient on temperature of the active element was measured. The small-signal gain coefficients per pass through active element were obtained.

Small-signal gain coefficient up to 1.2 per pass through active element is obtained experimentally in the laser multidisk amplifier of diode pumped solid state high peak and high average power laser system. The focal lengths of the thermal lenses are experimentally evaluated. Wavefront profiles are experimentally measured.

Holders of the active elements of a multi-disk multipass amplifier with a liquid-free closed cryogenic cooling cycle are modified. The equilibrium temperature of the active elements is experimentally investigated in relation to the power of diode pumping for the modified crystal holders. The dependence of the gain coefficient on the temperature of the active elements is measured. A small-signal gain of up to 1.2 is obtained in a single pass through the active element.

To supress beam pointing instabilities after high power laser multipass amplifier with cryogenic closed-loop cooling the copper heatsinks were optimized. Active elements’ temperature dependency on diode pump regimes is measured. The alternative seed laser for the high power laser multipass amplifier with cryogenic closed-loop cooling was modeled and designed.

The stabilization system implemented has allowed one to achieve phase residual instability similar to 0.17 radian (rms) for the 30 fs-pulse, which is sufficient for nonlinear interaction radiation with optical medium in forthcoming lightwave electronics experiments.

Temperature distribution in cryogenic cooled diode-pumped Yb:YAG crystal of multidisks high power laser system has been numerically calculated. Experimental investigation of dioptric power of the thermal lens and wavefront distortions by use of Shack-Hartman sensor has been performed. The obtained results are used for optimization of output beam parameters of pump channel of high intensity femtosecond laser system.

In this paper we focus on the second unit of multipass amplification of the cryogenic diode-pumped high power laser system operating at 1 kHz repetition rate. Thermal fields in the cooling system of the amplifier were calculated and compared with experimental data. Numerical algorithm based on 3+1D heat transfer equation is proposed. The results of modeling are discussed and analyzed

The optimization of the operation mode and spatiotemporal characteristics of the pump laser of Ti:Sa-femtosecond laser system was performed, which made it possible to reduce low-frequency noise in the frequency range from 30 Hz to 2.5 MHz of the output radiation to rms amplitude value of 0.005%. This has significantly increased the stability of the envelope phase stabilization system.

We have performed a numerical simulation of picosecond pulse propagation in a combined stretcher consisting of a segment of a telecommunication fibre and diffraction holographic gratings. The process of supercontinuum generation in a nonlinear photonic-crystal fibre pumped by picosecond pulses is simulated by solving numerically the generalised nonlinear Schrodinger equation; spectral and temporal pulse parameters are determined. Experimental data are in good agreement with simulation results. The obtained results are used to design a high-power femtosecond laser system with a pulse repetition rate of 1 kHz.

The calculation of parametric amplification unit based on nonlinear borate crystals for multiterawatt femtosecond laser system has been carried out. A Gaussian gain profile with a ~20% dip near the center is proposed to optimize the amplified signal spectral shape. Optimal parameters of the noncollinear type I BBO-based parametric amplifier were established.