High power laser systems operating at mid IR wavelengths are required for medical applications, environmental monitoring, and military applications. All of these systems require optical isolators to avoid feedback into the pump laser cavity. We present measurements of the Verdet coefficient of germanate glass with Dy concentrations varying from 20-50% at wavelengths between .4 and 1.5 microns. The results indicate a linear increase of the Verdet coefficient with impurity concentration and a Sellmeier like dependence on wavelength.
The refractive index of fully dense, infrared-transparent polycrystalline alumina (PCA) with a mean grain size of ∼0.6 μm is reported for the wavelength range 0.85 to 5.0 μm over the temperature range T=296 to 498 K. The temperature-dependent Sellmeier equation is n2−1=(A+B[T2−To2])λ2/[λ2−(λ1+C[T2−To2])2]+Dλ2/(λ2−λ22), where λ is expressed in μm, To=295.15 K, A=2.07156, B=6.273×10−8, λ1=0.091293, C=−1.9516×10−8, D=5.62675, λ2=18.5533, and the root-mean square deviation from measurements is 0.0002. This paper describes how to predict the refractive index of fully dense isotropic PCA with randomly oriented grains using the ordinary and extraordinary refractive indices (no and ne) of sapphire spatially averaged over the surface of a hemisphere. The refractive index of alumina at 296 and 470 K agrees within ±0.0002 with the predicted values. Similarly, the ordinary and extraordinary optical constants ko and ke are used to predict the absorption coefficient of alumina. The refractive indices no and ne of sapphire grown at Rubicon Technologies by the Kyropoulos method were measured at 295 K and agree with published Sellmeier equations for sapphire grown by other methods within ±0.0002.
The refractive index of polycrystalline α-alumina prisms with an average grain size of 0.6 μm is reported for the wavelength range 0.9 to 5.0 and the temperature range 293 to 498K. Results agree within 0.0002 with the refractive index predicted for randomly oriented grains of single-crystal aluminum oxide. This paper provides tutorial background on the behavior of birefringent materials and explains how the refractive index of polycrystalline alumina can be predicted from the ordinary and extraordinary refractive indices of sapphire. The refractive index of polycrystalline alumina is described by
where wavelength λ is expressed in μm, To = 295.15 K, A = 2.07156, B = 6.273× 10-8, λ1 = 0.091293, C = –1.9516 × 10-8, D = 5.62675, and λ2 = 18.5533. The slope dn/dT varies with λ and T, but has the approximate value 1.4 × 10-5 K-1 in the range 296–498 K.
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.