High power laser systems require the use of optical isolators to prevent coupling of reflected light into the pump laser. Terbium Gallium Garnet (TGG) and Potassium Terbium Fluoride (KTF) are materials used as optical isolators and while they have been grown for many years, advances in crystal growth and processing make a new set of measurements of the Verdet coefficients of these materials desirable. We present new measurements of the Verdet coefficients of TGG and KTF from 0.405 μ to 1.55 μ and derive expressions for the spectral behavior of the Verdet coefficients.
High power laser systems require optical isolators to avoid feedback into the pump laser cavity. To date, most of these devices have been based on the inverse Faraday effect in which the plane of polarization of the pump beam is rotated nonreciprocally in response to a magnetic field to prevent reflected light coupling back into the pump laser. Recently, new materials have been developed which have large Verdet coefficients and are able to withstand high optical power. We report measurements of the Verdet coefficient of potassium terbium fluoride and propose a design for an isolator based on this material.
Many scientific lasers and increasingly industrial laser systems operate in <500W and kW output power regime, require high-performance optical isolators to prevent disruptive light feedback into the laser cavity. The optically active Faraday material is the key optical element inside the isolator. SYNOPTICS has been supplying the laser market with Terbium Gallium Garnet (TGG - Tb3Ga5O12) for many years. It is the most commonly used material for the 650-1100nm range and the key advantages for TGG include its cubic crystal structure for alignment free processing, little to no intrinsic birefringence, and ease of manufacture. However, for high-power laser applications TGG is limited by its absorption at 1064nm and its thermo-optic coefficient, dn/dT. Specifically, thermal lensing and depolarization effects become a limiting factor at high laser powers. While TGG absorption has improved significantly over the past few years, there is an intrinsic limit. Now, SYNOPTICS is commercializing the enhanced new crystal Potassium Terbium Fluoride KTF (KTb3F10) that exhibits much smaller nonlinear refractive index and thermo-optic coefficients, and still exhibits a Verdet constant near that of TGG. This cubic crystal has relatively low absorption and thermo-optic coefficients. It is now fully characterized and available for select production orders. At OPTIFAB in October 2017 we present recent results comparing the performance of KTF to TGG in optical isolators and show SYNOPTICS advances in large volume crystal growth and the production ramp up.
Potassium terbium fluoride is a recently developed magneto-optic material which has been proposed for use as an optical isolator. We have performed measurements of the refractive index, thermo-optic coefficient, and stress-optic coefficient of this material. We present a temperature dependent Sellmeier equation along with calculations of temperature and refractive index profiles at various pump power levels in a diode pumped laser. The data are critical to the design of laser systems in which optical isolators are employed.
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