Mode locking with a slow saturable absorber in a transverse resonator

We report a new mode-locking technique, which greatly extends the number of dyes that can be used as saturable absorbers. When the absorber is enclosed in a high-Q transverse resonator its lifetime is reduced by stimulated emission to values that are sufficiently short to ensure complete recovery between passes. The technique has been demonstrated using rhodamine 6G for the amplifier and cresyl violet for the saturable absorber. In addition to its use for mode locking visible dye lasers, the technique also shows great promise for locking ultraviolet excimer lasers, such as krypton fluoride and xenon chloride lasers, using a visible dye for the slow saturable absorber.