Spectral filtering for mode locking in the normal dispersive regime

A theoretical model that characterizes the physical process responsible for generating ultrashort, high-energy, mode-locked pulses in a normal-dispersion laser cavity with strong spectral filtering is developed. According to this model, two of the critical physical parameters used to achieve optimal performance are the ratio of the filter bandwidth to the gain bandwidth and the placement of the output coupler in the laser cavity. The spectral filtering plays a crucial role in maintaining a short pulse duration with high energy. This phenomenon is generic to mode locking with normal dispersion. (C) 2008 Optical Society of America.