Abstract

Most solid-state lasers exhibit small gain cross-sections which require low- loss, fast saturable absorbers for passive mode-locking. In addition, the saturable absorber has to withstand high peak powers. Solid-state saturable absorbers are needed for an all-solid-state ultrafast laser technology. Recently, many new passive mode-locking techniques have been introduced which are either based on a real or on an effective fast saturable absorber. In the latter, one uses reactive nonlinearities to achieve fast saturable- absorberlike mode-locking. They, however, require either a sophisticated active cavity length control or are not self-starting. Fast semiconductor saturable absorbers can cover band gaps from the visible to the mid-infrared, but tend to introduce too much loss, have a low saturation intensity, and have problems to withstand the large intracavity peak intensities of solid-state lasers. As a result, they have been previously used inside a low-Q coupled cavity with resonant passive mode-locking (RFM¹). RPM is a coupled-cavity mode-locking technique using a real fast semiconductor saturable absorber inside a low-Q coupled cavity. Without an active cavity length control, RPM is self-stabilized in the time domain, at the expense however of small optical frequency fluctuations. Here we introduce a new intracavity semiconductor saturable absorber formed by a Fabry- Perot structure operated at antiresonance which is fast, low-loss, has a very high effective saturation intensity, requires no cavity length control, and produces stable self-starting cw mode-locked pulses.

© 1992 Optical Society of America