Terbium gallium garnet ceramic Faraday rotator for high-power laser application

Effective Faraday rotator based on the TbYO3 crystal with a high Verdet constant and a high thermal conductivity

Facing the demand of high-power laser development, a high-quality magneto-optical crystal with a high Verdet constant and a high thermal conductivity is needed. Herein, an effective Faraday rotation based on a TbYO3 single crystal with a strong magneto-optical effect, grown by the laser floating zone method, is demonstrated for the first time, to the best of our knowledge. The TbYO3 crystal has the Verdet constant which is 2.16 times (106 rad·m-1 T-1) higher than that of the TGG crystal (49 rad·m-1 T-1) at 880 nm. Additionally, the TbYO3 crystal also has a thermal conductivity of 11.8 W·m-1·K-1 and a laser-induced damage threshold of 1.59 GW·cm-2. These advantages can allow the TbYO3 crystal to be an attractive magneto-optical material.

Liquid Crystalline Magneto-Optically Active Peralkylated Azacoronene

Organic Faraday rotators have gained significant attention in recent years as a promising alternative to traditional inorganic magneto-optical (MO) materials as a result of their lower cost, superior mechanical properties, and potential for large-scale deployment. This interest is peaked by the fact that a number of high symmetry, rigid, strongly optically absorbing organic chromophores display Verdet constants an order of magnitude higher than commercial inorganic Faraday rotators. Critical to the development of new generations of organic materials is the ability to organize them in optimal structures for optical coupling/measurements. We report herein the synthesis of a dodecyl-substituted hexapyrrolohexaazacoronene (C₁₂-HPHAC) displaying discotic liquid crystalline (LC) properties and large Faraday rotation. Thin films with a redox mixed C₁₂-HPHAC/C₁₂-HPHAC⁺² composition display a discotic columnar LC phase, are stable to air and moisture in the solid and solution states, and achieve a maximum Verdet constant of 3.36 × 10⁵ deg T^-1 m^-1 at 700 nm. This result is consistent with Serber's model of magnetic circular birefringence and displays one of the largest reported Verdet constants for organic materials in the UV-Vis range. The LC phase aligns the molecules and leads to gains in Verdet constants of up to 105% through the favorable orientation of the molecules' magnetic and electric transition dipole moments with respect to the applied magnetic field.

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.

Progress in Transparent Nano-Ceramics and Their Potential Applications

Transparent nano-ceramics have an important high-transmittance, material-integrating structure and function and a variety of potential applications, such as use in infrared windows, optical isolators, composite armors, intelligent terminal screens, and key materials of solid-state lasers. Transparent ceramics were originally developed to replace single crystals because of their low fabricating cost, controllable shape, and variable composition. Therefore, this study reviews and summarizes the development trends in transparent nano-ceramics and their potential applications. First, we review the research progress and application of laser nano-ceramic materials, focusing on the influence of controllable doping of rare earth ions on thermal conductivity and the realization of large-scale fabrication technology. Second, the latest research progress on magneto-optical transparent nano-ceramics, mainly including terbium gallium garnet (Tb3Ga5O12, TGG) ceramics and terbium aluminum garnet (Tb3Al5O12, TAG) ceramics, are summarized, and their performance is compared. Third, the research progress of transparent armor nano-ceramic materials, represented by MgAl2O3 and Aluminum oxynitride (AlON), are reviewed. Lastly, the progress in electro-optical transparent nano-ceramics and scintillation transparent nano-ceramics is reported, and the influence of the material-fabrication process on electro-optic effect or luminous intensity is compared. Moreover, the effect of particle diameter on fabrication, the relationship between nano powder and performance, and different sintering methods are discussed. In summary, this study provides a meaningful reference for low-cost and sustainable production in the future.

Thermo-optical properties of terbium sesquioxide (Tb2O3) ceramics at room temperature

Thermo-optical properties of several (Tb_1-xY_x)₂O₃ ceramic samples were investigated in this Letter. The linear absorption and thermal conductivity coefficients, as well as the power dependence of thermally induced phase and polarization distortions of laser radiation, were measured. In addition, the effective thermo-optical constants P_eff and Q_eff were estimated. Thermo-optical properties of the studied ceramics were compared with those of the widely used terbium gallium garnet. It was shown that the material under consideration is highly promising for Faraday isolators operating at high average power laser radiation.

Thermo-Optical Studies of Laser Ceramics

A cycle of works on manufacturing and studying laser and magnetooptical ceramics with a focus on their thermo-optical characteristics performed by the research team is analyzed. Original results that have not been published before such as measurements of the Verdet constant in the Zr:TAG, Re:MgAl₂O₄, and ZnAl₂O₄ ceramics are also presented.

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.

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.

Faraday rotator based on TSAG crystal with <001> orientation

A Faraday isolator (FI) for high-power lasers with kilowatt-level average power and 1-µm wavelength was demonstrated using a terbium scandium aluminum garnet (TSAG) with its crystal axis aligned in the <001> direction. Furthermore, no compensation scheme for thermally induced depolarization in a magnetic field was used. An isolation ratio of 35.4 dB (depolarization ratio γ of 2.9 × 10^-4) was experimentally observed at a maximum laser power of 1470 W. This result for room-temperature FIs is the best reported, and provides a simple, practical solution for achieving optical isolation in high-power laser systems.

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.

Thermo-optical properties of terbium-aluminum garnet ceramics doped with silicon and titanium

The Verdet constant and thermo-optical characteristics of a Si-doped and Ti-doped terbium aluminum garnet ceramics have been investigated. It is shown that the Verdet constant of the samples is ∼40% higher than that of TGG ceramics at 1064 nm. The best samples of Si:TAG have magneto-optical figures of merit more than 1.5 times greater than those of TGG ceramics. Si:TAG is better than TGG ceramics as a medium for high-power Faraday isolators.

Wavelength dependence of magneto-optic properties of terbium gallium garnet ceramics

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.

Fabrication and characterization of cerium-doped terbium gallium garnet with high magneto-optical properties

High optical quality (Tb((1-x))Ce(x))₃Ga₅O₁₂ (TCGG) single crystal has been grown by the Czochralski method. The optical and magneto-optical properties of the TCGG are analyzed in detail and the Verdet constant (V) of TCGG is compared with that of undoped terbium gallium garnet (TGG) crystal. TCGG presents a very high transmittance, particularly in the visible-near infrared (VIS-NIR) region, and its V is obviously larger than that of TGG in the VIS-NIR region. The figure of merit and optical features point out the superior characteristics of TCGG with respect to TGG.