Thermo-optical parameters and dispersion of pure and Yb^3+-doped KY(WO_4)_2 laser crystals

Abstract

Dispersion of the principal refractive indices of pure and Yb(3+) (20 at.%)-doped KY(WO(4))(2) crystal is obtained in the visible range of the spectrum. A comparatively strong increase of the refractive indices (0.005-0.007) was observed for the doped crystal. Temperature dependence of the principal refractive indices is measured in the temperature region of 290-690 K. Thermo-optical coefficients (TOCs) of the first dn/dt and the second (1/2)(d(2)n/dT(2)) order are determined. It is found that TOCs are negative for n(p) and n(g) and positive for n(m) in both crystals. Doping increases dn(p)/dT almost two times more in comparison to that of the pure crystal, while for the other two indices TOC changes are insignificant.

Thermo-optic coefficients study in KGd(WO4)2 and KY(WO4)2 by a modified minimum deviation method

“…Indeed, observation of positive dn p ∕dT for KGdW and negative dn p ∕dT for KYW in [14][15] could be attributed to different prism orientations with respect to the crystallographic axes (principal axes of thermal expansion), while the orientation with respect to the optical indicatrix frame was the same. According to our research, thermo-optic coefficients for both crystals are negative, which is in agreement with other literature data in which the influence of thermal effect was taken into account.…”

“…1). The orientation of the prisms was identical to that of the one utilized in [14,15]. Prisms #2 and #3 (which were cut perpendicularly to the N m and N g axes) were identical for the KGdW and KYW crystals.…”

“…In using the laser beam deviation method and the interferometric one, the key point was to take into account the nonuniform thermal expansion effect, which causes changes in the shape and dimensions of the experimental sample [17][18][19]. In contrast, the conventional minimum deviation method does not take these changes into account [14,15]. In the present paper, such distortions were characterized for anisotropic KGdW and KYW crystals, resulting in the introduction of a modified minimum deviation method.…”

“…A similar conclusion was made in [19], where thermo-optic coefficients were determined in KGdW by the interferometer-based setup. On the contrary, according to [14,15], thermo-optic coefficients in KREW are different-signed: dn p ∕dT and dn m ∕dT are positive and dn g ∕dT is negative for KGdW, while only dn m ∕dT is positive and dn p ∕dT and dn g ∕dT are negative for KYW. The aim of the task described in this present paper was to resolve the discrepancy in the dn∕dT values determined in KREW crystals by different methods.…”

“…Power scaling of such lasers is restricted by the thermal lensing effect influence due to a moderate value of thermal conductivity (∼3 W∕mK) [10] and anisotropy of physical properties [11][12][13]. In addition, a significant discrepancy exists in the values of thermo-optic coefficients reported by different authors for these media [5,[14][15][16][17][18][19][20]. Optical properties of biaxial KREW are characterized by an optical indicatrix ellipsoid with three principal axes, namely N p , N m , and N g , and principal refractive indices n p <n m <n g [20][21][22][23].…”