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The principal spectroscopic and lasing characteristics of a Tm(15%) : KY(WO 4 ) 2 crystal were investigated. The transition cross sections, the luminescence quantum yield, and the lifetime and the nonlinear depopulation coefficient of the upper active state were also determined. The slope efficiency of lasing at the 1950 nm wavelength was 45%. The feasibility of tuning in the spectral range 18501 950 nm was demonstrated in principle. S N Bagaev, S M Vatnik, A P Maiorov, D V Plakushchev Institute of Laser Physics, Siberian Division of the Russian Academy of Sciences, prospekt akad. Lavrent'eva 13/3,

Abstract.A comparative study of thermal lensing effect in diode laser pumped N g -and N p -cut Nd:KGd(WO 4 ) 2 (KGW) laser crystals was performed for laser emission polarized along the principle refractive axis, N m . The thermal lens in the N g -cut Nd: KGW was found to be weakly astigmatic with a positive refractive power for both the N m -and N pdirections. For N p -cut Nd:KGW, strong astigmatism was observed and the refractive powers in the N g -and N m -directions had opposing signs. The degree of astigmatism was found to be considerably weaker for the N g -cut Nd:KGW in comparison with the N p -cut one: 0.35 dptr/(W/cm 2 ) and 2.85 dptr/(W/cm 2 ), respectively. The ratio of the thermal lens refractive powers in the planes parallel and perpendicular to the laser emission polarisation were measured as + 1.4 and −0.425 for N g -and N p -cut Nd:KGW respectively.

Abstract. The anisotropy of thermal lensing and the photo-elastic effect is characterized for diode-pumped Nd:KGd(WO 4 ) 2 crystals cut along the N p and N g optical indicatrix axes and along its optical axis, O = N g +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 N pand O-cut crystals; and it is positive for an N g -cut crystal. The increase of thermal lens optical power after absorption of 1 W of pump power, i.e. the thermal lens sensitivity factors M A(B) , and astigmatism degree S = |M A -M B | are determined. The photo-elastic effect was found to increase the optical power of thermal lens and was significant for all studied crystal orientations. [5][6][7][8] low-threshold diode-pumped lasers operating in the vicinity of 1 and 1.3 μm. KGW is a biaxial crystal, with three crystal orientations having been employed so far for laser engineering: along the b (N p ) axis [1][2][3][5][6][7][8], along the N g axis [9][10][11][12] and along the optical axis (O) [13,14], i.e. N g +43° in the N p -N g plane [15]. Strong astigmatism of the thermo-optical properties of the material results in significant variation in the sign and value of the thermal lens in crystals cut for light propagation along the N p and N g axes under diode-or flash-lamp pumping [9,12,15,16]. Thermal lens measurements were reported previously for the N p and N g -cut Nd:KGW crystals at the wavelength of 1.06 μm under the flash-lamp-pumping [9,15,16] and at the wavelength of 1.35 μm under the diode -pumping [12]. Keywords