Anisotropy of the photo-elastic effect in Nd:KGd(WO4)2 laser crystals

The anisotropy of thermal lensing and the photo-elastic effect is characterized for diode-pumped Nd:KGd(WO4)2 crystals cut along the Np and Ng optical indicatrix axes and along its optical axis, O = Ng+43°, at a laser wavelength of 1067 nm. Distortions in the spatial profile of output laser beam are analyzed. The thermal lens is astigmatic; the orientation of its principal meridional planes, A and B, is determined by the anisotropy of photo-elastic effect. The thermal lens has opposite signs for rays lying in the principal meridional planes for Npand O-cut crystals; and it is positive for an Ng-cut crystal. The increase of thermal lens optical power after absorption of 1 W of pump power, i.e. the thermal lens sensitivity factors MA(B), and astigmatism degree S = |MA–MB| are determined. The photo-elastic effect was found to increase the optical power of thermal lens and was significant for all studied crystal orientations.