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Faraday isolator with composite terbium gallium garnet TGG/sapphire magneto-optical elements that were produced by the surface-activated direct bonding method was created. Thermally induced depolarization and thermal lens for composite elements were investigated experimentally and numerically. The resulting structures operated successfully at a high radiation power, providing an isolation ratio exceeding the classical single element made of TGG by 5 dB and amounted to 34 dB at a laser power of 700 W. The maximum operating power at which the isolation ratio was higher than 30 dB was estimated to be over 2 kW, which is almost 3 times more than in the case of a single TGG. [ABSTRACT FROM AUTHOR]

Thermally induced distortions of laser radiation caused by the photoelastic effect during high-power beam propagation through optical elements cut along the optical axis of uniaxial crystals have been investigated. Thermo-optical characteristics for uniaxial crystals of all three syngony types have been introduced: the optical anisotropy parameter $\xi $ defining the distribution of the axes of thermally induced birefringence over the cross section of the optical element, and the thermo-optical constants $Q$ and $P$ specifying the value of thermally induced depolarization and thermal lens strength, respectively. The introduced thermo-optical characteristics may be used as applicability criteria of various uniaxial crystals for work with high-power laser radiation. The optical anisotropy parameter $\xi $ of trigonal and hexagonal crystals has been found to be equal to unity by virtue of the isotropy of their piezo-optical properties in a plane perpendicular to the optical axis. We have analyzed by way of example thermally induced polarization distortions in a tetragonal DKDP crystal and in a trigonal CeF3 crystal. The distributions and dependences observed in experiment fully agree with the theoretical considerations. [ABSTRACT FROM PUBLISHER]

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 $\xi $ , 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. [ABSTRACT FROM AUTHOR]

A cryogenic Faraday isolator based on terbium-gallium garnet (TGG) ceramics has been designed and studied in experiments. Its performance capabilities at the laser radiation power of 435 W are demonstrated, and our models suggest that the isolator should perform up to 2 kW. Thermal effects-thermally induced depolarization and thermal lens in the TGG ceramics in the 89-293 K temperature range are investigated. It is shown that the TGG ceramics compares well to the TGG monocrystal as a medium for Faraday isolators, including cryogenic ones. At the same time, in contrast to the TGG monocrystal, ceramics allows creating large-aperture Faraday isolators for lasers with high-average and high-peak power. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The small signal gain and phase and polarization distortions of laser radiation have been investigated theoretically and experimentally in end-pumped Yb:YAG thin-disk and Yb:YAG/YAG composite active element under nonlasing conditions. Comparison of experimental data with calculation results reveals an additional heat release whose negative influence is three times stronger than that of amplified spontaneous emission in the thin-disk active element. [ABSTRACT FROM PUBLISHER]