Balancing Orthogonal Polarizations in Ytterbium-Doped Isotropic-Crystal Lasers: Effect of Crystal Disorder

Ytterbium lasers are widely used for femtosecond pulse generation. In the context of dual-comb spectroscopy, the use of an isotropic crystalline host permits the oscillation of two eigenstates of orthogonal polarizations, providing frequency combs whose repetition rates are adjustable [1]. In order to balance the powers of both polarization modes, the use of a polarized pump can create a gain dichroism, as already demonstrated in Vb:YAG [2]. Here we present new experimental results on a series of Yb<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>-doped isotropic crystals. In particular we show that, while dual-polarization oscillation is always possible, the gain anisotropy induced by the pump is strongly host-dependent, especially due to the crystal disorder.