Abstract

Recently, we have shown that in the presence of solitonlike pulse shaping, a slow saturable absorber alone with a recovery time much longer than the soliton width can stabilize the pulse.¹ This is in contrast to the traditional concepts of ultra short-pulse generation, which rely either on a fast saturable absorber, as is the case for APM or KLM systems, or on the interplay between a slow saturable absorber and gain saturation, as is the case for dye lasers. This is possible in the soliton regime because for the soliton the nonlinear effects due to SPM and the linear effects due to the negative group-velocity dispersion are in balance. In contrast, the noise or instabilities that would like to grow are not intense enough to experience the nonlinearity and are therefore spread in time. However, when they are spread in time, they experience higher absorption due to the slowly recovering absorber after passage of the solitonlike pulse. Thus the instability modes see less gain per round trip than does the soliton, and they will decay with time. Our experiments supporting this theory include Nd:glass lasers with sub-100-fs pulses² and a diode-pumped Cr:LiSAF laser producing 40-50-fs pulses.³ The pulses are always transform limited because of their solitonlike nature.

© 1995 Optical Society of America