Optical bistability and hysteresis in a colliding pulse mode locked femtosecond dye laser

We describe the observation of optical bistability in a colliding pulse mode locked dye laser. Two lasing states can occur, one at 612 nm and with femtosecond pulse formation and the other at 570 nm and with a c.w. output. An hysteresis loop can be obtained plotting the output power as a function of the pump laser power. Control of the hysteresis can be accomplished by changing the beam focusing over the saturable absorber.