Thermal lens in laser-diode-pumped self-frequency-doubled Nd,Lu:YAl/sub 3/(BO/sub 3/)/sub 4/ laser with and without laser oscillations

A new self-frequency-doubling Nd,Lu:YAl/sub 3/(BO/sub 3/)/sub 4/ (NLYAB) crystal, in which a part of the Y/sup 3+/ ion is replaced by the Lu/sup 3+/ ion according to the volume compensation theory for improving the crystal quality, has nearly the same physical properties and better crystal quality compared with NYAB. The laser-diode (LD) pumped NLYAB laser has the possibility of providing a compact and efficient coherent light source in the visible region. In general, thermal lensing reduces laser efficiency and degrades beam quality. Qualitative estimation of the thermal lens in the crystal is very important for optimizing laser performance. Recently, several researchers have suggested that at high excitations typically found under non-lasing conditions, non-radiative relaxation increases the heat load and, hence, induces strong thermal lensing. In this paper, we present a quantitative comparison between the thermal lens under lasing and non-lasing conditions in a LD pumped NLYAB laser using the lateral-shearing interferometric technique.