We review the progress in the investigation of the Verdet constant of new magneto-active materials for the Faraday-effect-based devices used in high-power laser systems. A practical methodology for advanced characterization of the Verdet constant of these materials is presented, providing a useful tool for benchmarking the new materials. The experimental setup used for the characterization is a flexible and robust tool for evaluating the Faraday rotation angle induced in the magneto-active material, from which the Verdet constant is calculated based on the knowledge of the magnetic field and the material sample parameters. A general model for describing the measured Verdet constant data as a function of wavelength and temperature is given. In the final part of this review, we present a brief overview of several magneto-active materials, which have been to-date reported as promising candidates for utilization in the Faraday devices. This overview covers room-temperature investigations of the Verdet constant of several materials, which could be used for the ultraviolet, visible, near-infrared and mid-infrared wavelengths.

A polarization-stepping method for measurement of the Faraday rotation in magneto-active materials has been modified for evaluating the Verdet constant as a function of wavelength and temperature. It has been used for a comparison of wavelength and temperature dependent Verdet constant, dominant electronic transition wavelength, and Curie-Weiss temperature in terbium gallium garnet (TGG) single crystals and TGG ceramics samples. The room-temperature values of Verdet constant varied from 36.6 to 44.2 rad/T.m at 1.064 μm wavelength and from 122.4 to 155.5 rad/T.m at 0.632 μm wavelength for all samples under investigation. These results match very well the values obtained from single wavelength measurement in the literature and show the same measurement error for single crystal and ceramics, respectively. The Curie-Weiss temperature has been evaluated for the first time in TGG ceramics. This method could be used for the detailed characterization of magneto-optical properties of the materials over a wide range of wavelengths and temperatures which is of great importance for the proper design of Faraday devices.

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 ∼ $2 \times 10^{12}$ 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.

An overview of the latest developments of kilowatt-level diode pumped solid state lasers for advanced applications at the HiLASE Centre is presented. An overview of subcontracted and in-house-developed laser beamlines is presented. The aim of development is to build kW-class beamlines delivering picosecond pulses between 1- and 100-kHz repetition rates and high-energy nanosecond pulses at 10 Hz. The picosecond beamlines are based on Yb:YAG thin-disk amplifiers and chirped pulse amplification. The current status of the beamlines’ performance is reported. The advantages of zero-phonon line and pulsed pumping are demonstrated with respect to efficiency, thin disk temperature and beam quality. New diagnostics methods supporting the high average power lasers’ development, such as the high-resolution spectroscopy of Yb-doped materials, in situ thin disk deformation measurements, single-shot M² measurement, realization of wavefront correction by a deformable mirror and the laser performance of a new mixed garnet ceramics, are described. The energetic, thermal and fluid-mechanical numerical modeling for the optimization of the multi-slab amplifiers is also described.

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.

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.