Nd:YVO4 laser mode locked by cascading of second order nonlinearities

Experimental results on an end pumped CW Nd:WO, laser mode locked using cascading of second order nonlinearities in an intracavity KTP crystal are reported. The mode locking technique exploits the nonlinear transverse phase distortion arising during second harmonic generation and parametric back conversion and is demonstrated for the first time with a type II phase matched nonlinear crystal (KTP). Pulses of 6.8 ps have been obtained. For compensation of the group velocity mismatch in the nonlinear crystal a technique, whose effectiveness was previously only proved in combination with type I phase matching, has been demonstrated to be also successfully applicable with type II phase matching. This technique is based on the use of an intracavity birefringent crystal. The compensation method has also been applied to the same laser mode locked by the nonlinear mirror technique and pulses of comparable duration have been obtained. (C) 1998 Elsevier Science B.V. All rights reserved.