Thermal lensing in Yb:KLu(WO₄)₂crystals cut along the optical indicatrix axes

Abstract

Thermal lensing is studied in Yb:KLu(WO 4 ) 2 crystals cut along the three optical indicatrix axes, N p , N m and N g . The cut along the N g -axis is the only one that provides a pure positive thermal lens with the sensitivity factors M = 3.5 and 2.8 m −1 W −1 (w p = 100 μm) for the mg-and pg-planes, respectively, and a low astigmatism degree, S/M < 20%. Both N p -cut and N m -cut crystals produce different-signed lens with at least six-times stronger astigmatism. This behavior is related to the anisotropy of the photo-elastic effect. A CW Yb:KLu(WO 4 ) 2 microchip laser delivering a maximum output power of 992 mW at 1051 nm with a slope efficiency of 40%, and possessing low spatial distortions of the laser beam and M 2 < 1.1, is realized on the basis of N g -cut crystal.

Prospects of monoclinic Yb:KLu(WO_4)_2 crystal for multi-watt microchip lasers

“…3(a). Here symbols represent direct measurements for E || N m , for details see [20]. Lines denote the calculation of the so-called sensitivity factor of the thermal lens M, amounting to +3.5 and +2.8 m -1 /W for directions || N p and || N m , respectively.…”

Watt-level ultrafast laser inscribed thulium waveguide lasers

“…The thermo-optical effects in MDTs can be greatly suppressed owing to their "athermal" behavior [51,52], i.e., a mutual compensation of contributions to the variation of the optical path length arising from the negative thermo-optic coefficients (dn/dT < 0) [53] and positive thermal expansion [54]. These properties lead to a weak, positive and nearly spherical thermal lens for certain crystal orientations with a reduced effect on the laser mode [55][56][57][58][59].…”