Thermo-optic coefficients anisotropy was characterized in monoclinic potassium (rare-earth) double tungstates KGd(WO4)2 and KY(WO4)2 in the spectral range of 0.44–0.63 μm by a modified minimum deviation method. This approach takes into account the changes in the shape and dimensions of the prismatic sample caused by the anisotropic thermal expansion effect under uniform heating together with the conventional measurements of minimum deviation angle. At room temperature at the wavelength of 633 nm, principal refractive indices for KGdW are np=2.0135, nm=2.0458, and ng=2.0860, and for KYW they are np=1.9979, nm=2.0396, and ng=2.0869. Optical axes position for KGdW (KYW) crystals is Ng±42.60 (Ng±44.1°) in the Np−Ng plane. For both crystals, all the thermo-optic coefficients are negative and equal dnp/dT=−10.6, dnm/dT=−8.4, and dng/dT=−15.2 for KGdW, and dnp/dT=−10.1, dnm/dT=−7.3, and dng/dT=−8.4 for KYW [10−6 K−1] (at 633 nm).
© 2012 Optical Society of America
Lasers and Laser Optics
Original Manuscript: December 5, 2011
Revised Manuscript: January 25, 2012
Manuscript Accepted: January 26, 2012
Published: May 18, 2012
Pavel A. Loiko, Valery V. Filippov, Konstantin V. Yumashev, Nikolai V. Kuleshov, and Anatoly A. Pavlyuk, "Thermo-optic coefficients study in KGd(WO4)2 and KY(WO4)2 by a modified minimum deviation method," Appl. Opt. 51, 2951-2957 (2012)