Mapping of the second-harmonic nonlinear mirror characteristics for laser mode locking and pulse shortening

The mode-locking capability of the double-pass nonlinear mirror in dependence on phase mismatch in crystal and the relative phase shift between two passes are studied. The regions of the most efficient pulse shortening on the plane of these parameters are determined both theoretically and experimentally. Their locations are dependent on a light intensity and occupy the area substantially detuned from phase-matching conditions in crystal and pure downconversion conditions for interpass phase shift. It is shown that the possibility of stable pulse formation exists provided that a certain intensity threshold is achieved. (C) 1998 Optical Society of America.