Characterisation of nonlinear conversion and crystal quality in Nd- and Yb-doped YAB

Variable crystal quality affects the laser performance of many self-frequency doubling crystals, particularly those of the yttrium aluminum borate family. In this report we characterize nonlinear frequency conversion in Yb:YAB and demonstrate a simple non-destructive technique for measuring crystal quality. By imaging the nonlinear conversion using a CCD camera we observe phase matching characteristics similar to that obtained in quasi-phase-matched crystals. These effects are attributed to stacking faults in the structure of the YAB crystal during crystal growth. We believe that such defects cause the large variability in self-doubled performance reported for Nd- or Yb-doped YAB and that our technique may be used as a nondestructive measurement of crystal quality.