Abstract
We show that the transient spectrum of a continuous-wave Ti:sapphire laser during the initial stage of the buildup, which exhibits multiple clusters (of longitudinal modes), is due to the spectral windowing effect of the Brewster-angle-cut Ti:sapphire crystal, which acts as a birefringent filter in the laser cavity. This effect is also responsible for certain spectral features of a passively mode-locked Ti:sapphire/DDI laser. © 1992 Optical Society of America.