Investigation of thermo-optical characteristics of magneto-active crystal Na(0.37)Tb(0.63)F(2.26)

Fabrication and characterization of a gadolinium-doped terbium gallium garnet crystal with an enhanced Verdet constant

Magneto-optical materials based on Tb₃Ga₅O₁₂ (TGG) crystals offer promising opportunities when used in modern Faraday isolators (FIs). Gadolinium (Gd)-doped TGG (Gd:TGG) crystals with high transmittance were prepared using the Czochralski (Cz) method. The as-prepared crystal presented a high optical transmittance of up to 80.0% in the range from 520 nm to 1520 nm. The Verdet constants of the as-grown crystal at 405.0, 533.0, 632.0, and 1064.0 nm were -583.0, -230.1, -150.3, and -50.3 rad m^-1 T^-1, respectively. The measured value at 1064 nm was about 1.3 times stronger than that of TGG. Thus, it could minimize the strength of the magnet of Faraday rotators. These excellent characteristics make Gd:TGG single crystal an attractive magneto-optical material.

Growth Peculiarities and Properties of KR3F10 (R = Y, Tb) Single Crystals

Cubic KR3F10 (R = Y, Tb) single crystals have been successfully grown using the Bridgman technique. Growth of crystals of this type is complicated due to the hygroscopicity of potassium fluoride and melt overheating. The solution to the problem of oxygen-incorporated impurities has been demonstrated through the utilization of potassium hydrofluoride as a precursor. In this study, the crystal quality, structure features, and optical, thermal and electrophysical properties of KR3F10 were examined. Data on the temperature dependences of conductivity properties of KTb3F10 crystals were obtained for the first time. These crystals indicated thermal conductivity equal to 1.54 ± 0.05 Wm−1K−1 at room temperature caused by strong phonon scattering in the Tb-based crystal lattice. Ionic conductivities of KY3F10 and KTb3F10 single crystals were 4.9 × 10−8 and 1.2 × 10−10 S/cm at 500 K, respectively, and the observed difference was determined by the activation enthalpy of F− ion migration. Comparison of the physical properties of the grown KR3F10 crystals with the closest crystalline analog from the family of Na0.5−xR0.5+xF2+2x (R = Tb, Y) cubic solid solutions is reported.

Thermal lens astigmatism in glass and in cubic crystals with [001] orientation

The thermal lens was investigated in CaF₂ and Tb₃Ga₅O₁₂ cubic crystals with [001] crystallographic axes orientation and in magneto-optical glass MOG103 by the method of phase-shifting interferometry. It was demonstrated experimentally that the thermal lens has astigmatism determined by the incident radiation polarization state and by the optical anisotropy parameter ξ. A method of ξ determination by measuring thermal lens astigmatism in cubic crystals with [001] orientation was proposed and verified. It was shown that thermally induced depolarization and the amplitude of phase astigmatism depend on the position of the crystal with [001] orientation in antiphase.

Verdet constant of potassium terbium fluoride crystal as a function of wavelength and temperature

Potassium terbium fluoride KTb₃F₁₀ (KTF) crystal is a promising magneto-active material for creating multi-kilowatt average-power Faraday isolators operating at the visible and near-infrared wavelengths. Nevertheless, the key material's parameter needed for the design of any Faraday isolator-the Verdet constant, has not been comprehensively investigated yet. In this Letter, we report on measurement of the Verdet constant of the KTF crystal for wavelengths between 600 and 1500 nm and for temperatures ranging from 15 to 295 K. A suitable model for the Verdet constant as a function of wavelength and temperature has been developed and may be conveniently used for optimal design of KTF-based high-average-power Faraday isolators.

Verdet Constant of Magneto-Active Materials Developed for High-Power Faraday Devices

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.

High-power Faraday isolator on a uniaxial CeF3 crystal

We have created the first high-power Faraday isolator on an anisotropic magneto-optical element (MOE). The isolator is based on one MOE of a uniaxial CeF₃ crystal and ensures an isolation degree of 30 dB at a high average laser radiation power of 700 W. The limitations due to the anisotropic nature of the crystal do not impose significantly more stringent requirements, either for the beam or the MOE.

Total Performance of Magneto-Optical Ceramics with a Bixbyite Structure

High-quality magneto-optical ceramics (Tb_xY_1-x)₂O₃ (x = 0.5⁻1.0) with a Bixbyite structure were extensively investigated for the first time. The total performances of these ceramics were far superior to those of commercial TGG (Tb₃Ga₅O₁₂) crystal, which is regarded as the highest class of Faraday rotator material. In particular, the Verdet constant of Tb₂O₃ (when x = 1.0) ceramic was the largest-495 to 154 rad·T^-1·m^-1 in the wavelength range of 633 to 1064 nm, respectively. It was possible to further minimize the Faraday isolator device. The insertion loss of this ceramic was equivalent to that of the commercial TGG single crystal (0.04 dB), and its extinction ratio reached more than 42 dB, which is higher than the value for TGG crystal (35 dB). The thermal lens effect (1/f) was as small as 0.40 m^-1 as measured by a 50 W fiber laser. The laser damage threshold of this ceramic was 18 J/cm², which is 1.8 times larger than that of TGG, and it was not damaged during a power handling test using a pulsed laser (pulse width 50 ps, power density 78 MW/cm²) irradiated at 2 MHz for 7000 h.

Magneto-optical Faraday effect in dysprosium oxide (Dy2O3) based ceramics obtained by vacuum sintering

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 (Dy_xY_0.95-xLa_0.05)₂O₃, 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 Dy³⁺ 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 Tm³⁺ and Ho³⁺ lasers and for lasers emitting in the visible spectrum.

Polycrystalline (TbXY1-X)2O3 Faraday rotator

We have succeeded for the first time in synthesizing an optical grade (Tb_XY_1-X)₂O₃ (X=0.5-1.0) ceramic Faraday rotator, which greatly exceeds the basic characteristics of the commercial terbium gallium garnet (TGG) (Tb₃Ga₅O₁₂) crystal. The Faraday rotation angle increased as the Tb concentration increased, and the Verdet constant increased from 2.1 (82  rad T^-1 m^-1 at X=0.5) to 3.8 times (154  rad T^-1 m^-1 at X=1.0) than the TGG single crystal, which is regarded as highest class. Therefore, it is possible to minimize the Faraday rotator length and the magnet in building an optical isolator. It was also confirmed that its optical quality was very comparable to the commercial TGG crystal.

High magneto-optical characteristics of Holmium-doped terbium gallium garnet crystal

Magneto-optical characteristics of a new magneto-active material, (Tb_(1-x)Ho_x)₃Ga₅O₁₂ crystal, have been grown by the Czochralski (Cz) method. A high value of the Verdet constant was obtained at room temperature-namely, 214.9 and 77.8  rad·m^-1 T^-1 for 632.8 and 1064 nm, respectively. The Verdet constant of the Ho-doped terbium gallium garnet crystal at 1064 nm is about 2 times higher than that of terbium gallium garnet crystal. High value of magneto-optical figure-of-merit makes it an attractive next-generation magneto-optics material for high-power Faraday isolators.