Samples of the magneto-active material—Tb³⁺:Y₂O₃ ceramics with Tb³⁺ ion concentrations of 10%, 20%, 30%, and 100% (Tb₂O₃)—were prepared and studied. The wavelength dependence of Verdet constant in the 380 nm–1750 nm range was approximated for all investigated ceramic samples and was predicted for a pure Tb₂O₃ material. Tb₂O₃ ceramics demonstrates a more than three times higher Verdet constant in comparison with terbium gallium garnet crystal or ceramics. The linear dependence of the Verdet constant on Tb³⁺ ion concentration in the Tb³⁺:Y₂O₃ ceramics was demonstrated. The obtained data will be useful for fabricating magneto-optical elements of Faraday devices based on Tb³⁺:Y₂O₃ with arbitrary Tb³⁺ ion concentration operating at room temperature in the wavelength range of 380 nm–1750 nm.

Faraday isolators for high average power lasers operating at room temperature are surveyed. Three devices on [001] oriented TGG crystals with the most known optical schemes are considered: traditional scheme, and schemes with compensation of thermally induced depolarization inside magnetic field and outside magnetic field. We report a unique 30-mm-aperture Faraday isolator with thermally induced depolarization compensation inside magnetic field. It provides 33.5-dB isolation ratio at 1.5-kW average laser power.

The method of self-propagating high-temperature synthesis of submicron powders with subsequent vacuum sintering was used to produce a series of optical ceramics based on dysprosium oxide $({\mathrm{Dy}}_x{\mathrm{Y}}_{0.95-x}{\mathrm{La}}_{0.05}{)}_2{\mathrm{O}}_3$, where $x=0.7$, 0.85, and 0.9. The influence of ceramics composition on optical transmission of the obtained samples was investigated. The studied materials had several transparency windows in the visible 500–730 nm, near-IR 1900–2300 nm, and mid-IR 3500–7500 nm ranges. The dependence of the Verdet constant on wavelength in the 400–1940 nm range was measured for each ceramics composition, and analytical approximations were obtained. When Y and La dopants were used, the Verdet constant depended linearly on the concentration of ${\mathrm{Dy}}^{3+}$ ions, and its value in the visible wavelength range was about twice that of the analogous value for a terbium gallium garnet crystal. The high transmission and relatively high Verdet constant make the produced materials highly promising for fabricating Faraday devices for ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Ho}}^{3+}$ lasers and for lasers emitting in the visible spectrum.

Magnetoactive materials are of considerable current interest, primarily for applications in nonreciprocal Faraday devices used for polarization control, optical isolation, optical switching, and modulation. The need for such devices is growing with laser power enhancement. They reduce risk of self-excitation of the amplifiers and optical elements damage and are a handy tool for organizing multipass schemes. However, at high average power of radiation these devices are subject to thermally induced effects that impair their operability and lead to increased losses and to the formation of phase distortions in the transmitted radiation. One of the methods to reduce thermally induced effects is to use in Faraday devices new magnetoactive materials with better thermo-optical properties. This paper is devoted to the study of thermo-optical and magneto-optical characteristics of a unique magnetoactive material-a terbium scandium aluminum garnet (TSAG) crystal. The TSAG has an extraordinary value of optical anisotropy parameter ξ, a Verdet constant 25% higher than the traditionally used terbium gallium garnet crystal and the highest magneto-optical figure-of-merit known in magnetoactive materials at the moment.

A terbium gallium garnet (TGG) ceramic Faraday rotator (FR) with an isolation ratio of 33 dB was demonstrated at a laser radiation power of 257 W. This FR can be equipped with a large optical aperture by using ceramics technology to prevent laser damage at high-energy pulse operation. The thermal lens of a 257 W laser with a beam diameter of 2.6 mm had a focal length of 9.5 m, which is easily corrected using a spherical lens to suppress the undesirable effects of thermal lensing. The rotation angle of the FR was stabilized by water cooling. The results indicate that the TGG-ceramic-based FR is suitable for high-energy laser systems with high repetition rates.

The key importance of the sign of the stress-optic anisotropy ratio for reducing thermally induced depolarization in cubic crystals with 432, $\overline{4}3m$ and m3m symmetry is addressed. A simple method for measuring the stress-optic anisotropy ratio (including its sign) was proposed and verified in CaF₂ and TGG crystals by experiment. The ratio at room temperature for the wavelength 1076 nm was measured to be −0.47 and + 2.25, respectively. In crystals with a negative value of this parameter thermally induced depolarization may be reduced significantly by choosing crystal orientation. In a CaF₂ crystal with the [111] orientation a 20-fold reduction of thermally induced depolarization as compared to the [001] orientation was obtained in experiment, which is very promising for using CaF₂ as an active element in high-average-power lasers.