Faraday isolator1/6/2023 ![]() A first set of measurements of the thermal lensing has been used to characterize the losses of the crystal, which depend on the sample. A finite element model simulation reproduces with a great accuracy the experimental data measured on Virgo and on a test bench. An isolation decrease by a factor of 10 is experimentally observed in a Faraday isolator that is used in a gravitational wave experiment (Virgo) with a 10 W input laser when going from air to vacuum. The changes are particularly significant in the crystal thermal lensing (refraction index and thermal expansion) and in its Verdet constant and can be ascribed to the less efficient convection cooling of the magneto-optic crystal of the Faraday isolator. ![]() We describe a model evaluating changes in the optical isolation of a Faraday isolator when passing from air to vacuum in terms of different thermal effects in the crystal. In further, the relationships between Verdet constant and wavelength of TSAG and TSLAG are obtained. Moreover, the Verdet constants of TSAG are 218, 152, and 65 rad/m/T at 532, 633, and 1064 nm, while those of TSLAG are 246, 146, and 56 rad/m/T, respectively. Calculated with the specific heat results, the values of thermal conductivity of TSAG and TSLAG are 4.45 and 4.20 W (m K)⁻¹ at 300 K. The thermal diffusivity values of TSAG and TSLAG are 1.454 and 1.418 mm² s⁻¹ at 300 K, respectively. The values of thermal expansion coefficients of TSAG and TLSAG crystals coincide within the measurement error (differ by 0.3–0.4%). The average thermal expansion coefficients of TSAG and TSLAG at 300 – 373 K, 300 – 473 K, 300 – 573 K, 300 – 673 K, and 300 – 773 K are measured. Large size high transparent TSAG and TSLAG single crystals of Ø 65 mm × 70 mm have been grown successfully by the Cz method. In summary, the appropriate initial molar ratio range for synthesizing pure TGG polycrystalline is Tb: Ga = 3 : 4.75–5.15, and the best calcination temperature is 1200☌. The X-ray photoelectron spectroscopy (XPS) analysis shows that there is no or little Tb⁴⁺ ion existed in samples after being calcined at or above 900☌. The chemical stoichiometric ratios change and Ga element loss were investigated with X-ray fluorescence (XRF) analysis and found that loss rate of Ga element is close to 23% after calcined at 1200☌ or higher temperatures for 48 h. The tri-terbium gallate dioxide (TGD) was found as a metastable phase, which disappeared at no more than 1200☌. Some of the Ga2O3 from the starting material and Tb2O3 formed at high temperature gradually disappeared at no more than 1100☌. The phases transition was semi-quantitatively investigated with X-ray diffraction (XRD) and Rietveld refinement. In this work, the commercial Ga2O3 powder and Tb4O7 were selected as starting raw materials, and the samples with various initial chemical stoichiometric ratios were calcined at the different temperatures. ![]() However, the phases transitions, Ga component volatilization and the valence of Tb element during synthesizing TGG polycrystalline with Tb4O7 and Ga2O3 were not been reported previously. It was found that the TGG polycrystalline reacting completely was very important for good-quality single crystal growth. Terbium gallium garnet (Tb3GaxO12, TGG) is an excellent magneto-optical material and widely used in magneto-optical isolators of laser systems, it is an important topic to grow large-size and high-quality single crystal. ![]() 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. 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. ![]() A general model for describing the measured Verdet constant data as a function of wavelength and temperature is given. 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 practical methodology for advanced characterization of the Verdet constant of these materials is presented, providing a useful tool for benchmarking the new materials. 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. ![]()
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