Ondrej Slezak

High-Contrast, High-Intensity Petawatt-Class Laser and Applications

A high-contrast high-intensity petawatt-class Ti:sapphire chirped-pulse amplification laser has been developed for research on high field science. A saturable absorber and a low-gain optical parametric chirped-pulse amplification preamplifier in the front-end have improved the temporal contrast in the system to ∼

Design of high-energy-class cryogenically cooled Yb3+∶YAG multislab laser system with low wavefront distortion

2 times 10^{12}

Optimization of Wavefront Distortions and Thermal-Stress Induced Birefringence in a Cryogenically-Cooled Multislab Laser Amplifier

on the subnanosecond time scale at the ∼70 TW power level. In addition to the high-contrast broadband high-energy output from the final amplifier has been achieved with a flat-top spatial profile with a filling factor of ∼70%. This is the result of pump beam spatial profile homogenization with diffractive optical elements. The system produces the uncompressed output pulse energy of 29 J, indicating the capability for reaching a peak power of ∼600 TW. We discuss in detail the design, performance, and characterization of the laser including output power, pulse duration, and spatiotemporal beam quality. We also describe the on-going upgrade of the laser system and some applications for the laser in relativistic dominated laser–matter interactions.

Wavelength dependence of magneto-optic properties of terbium gallium garnet ceramics

Abstract. Detailed modeling results of 100 J class laser systems with respect to the output energy, beam propagation, nonlinear phase accumulation, wavefront aberrations, and adaptive optics performance obtained in MIRÓ and MATLAB codes are presented here. The laser system is based on a cryogenically cooled Yb3+∶YAG multislab amplifier with two identical amplifier heads and operates at 10 Hz repetition rate with an average power above 1 kW.

Design and optimization of an adaptive optics system for a high-average-power multi-slab laser (HiLASE)

The optimization of the Yb:YAG gain medium and absorbing clad parameters was investigated for efficient heat removal in cryogenically-cooled multislab amplifiers operating in the kilowatt average power range (100 J/10 Hz). The 3-D distributions of temperature, stress, strain, and birefringence were calculated by a finite element analysis. Based on these data, the space-resolved optical path difference and depolarization losses were determined considering eight slabs, two laser heads, and four passes. We have found that a combination of properly designed (doping/width) index matching material and helium cryogenic cooling leads to a quasi-constant transverse temperature distribution in the pump area and a very small axial thermal gradient in the slab. It is shown that the resulting thermally induced phase aberrations, stresses, and average depolarization are rendered insignificant.

HiLASE cryogenically-cooled diode-pumped laser prototype for inertial fusion energy

The wavelength dependence of magneto-optic properties of TGG ceramics, including the Verdet constant, has been investigated experimentally. The previously obtained Verdet constant of 36.4 rad/Tm for 1064 nm wavelength and 139.6 rad/Tm for 633 nm are in good agreement with presented white light measurements . The comparison with previously reported Verdet constant and absorption coefficient values for TGG single crystal has shown very similar results. These results lead to the conclusion that TGG ceramics is a very good alternative to TGG single crystal and is a powerful approach for realizing large-aperture optical isolators which are required in high-average-power laser systems.

Simulation of performance of wavefront correction using deformable mirror in high-average-power laser systems

We report numerical and experimental results obtained with an optical setup that simulates the heating and cooling processes expected in a multi-slab high-average-power laser head. We have tested the performance of an adaptive optics system consisting of a photo-controlled deformable mirror (PCDM) and a Shack-Hartmann wavefront sensor for the effective correction of the generated wavefront aberrations. The performance of the adaptive optics system is characterized for different layouts of the actuator array and for different configurations of the heating mechanisms. The numerical results are benchmarked using a PCDM, which allowed us to experimentally compare the performances of different deformable mirrors.

Verdet constant dispersion of CeF3 in the visible and near-infrared spectral range

We present the design parameters of a diode-pumped 100J-class multi-slab Yb:YAG laser at 10 Hz scalable to the kJ regime. Results of detailed energetics and thermo-optical modeling confirm the viability of cryogenic helium-gas cooling approach to drastically reduce thermally-induced distortions in the laser slabs. In addition, a comparison of spectral measurements from laser-diode stacks and Yb:YAG crystals validates the feasibility of highly efficient diode-pumped solid-state lasers at cryogenic temperatures.

HiLASE: a scalable option for Laser Inertial Fusion Energy

We present calculation of aberration compensation in high average power multi-slab laser by a deformable mirror. The calculations were compared with a simple experiment. For the calculations we have developed a code that works with a square-shaped piston driven push/pull deformable mirror with continuous facesheet and allows optimization of mirror parameters and actuator array geometry. We have corrected the calculated output wavefront of Hilase 10 J multi-slab laser system in MIRÓ by using several actuator array geometries. The numerical results were benchmarked on an experimental model of multi-slab chamber using a membrane deformable mirror.

HiLASE: development of fully diode pumped disk lasers with high average power

Abstract. The Verdet constant dispersion of CeF3 crystal was measured in the spectral range from 0.45 to 1.95u2009u2009μm. To the best of our knowledge, CeF3 crystal was investigated for the first time as a potential material candidate for near-infrared Faraday rotators (FRs). The experimental results obtained for Verdet constant dispersion were compared to other magneto-optical materials with the conclusion that CeF3 crystal possesses up to 60% higher Verdet constant in the near-infrared spectral region 1.1 to 1.5u2009u2009μm compared to widely used terbium gallium garnet crystal. Furthermore, the presented experimental setup is capable of high precision measurement of Verdet constant dispersion in a broad spectral range, with measurement error not exceeding 5%, therefore, representing a powerful tool for FRs development.