Tunable passive colliding-pulse mode locking in a linear dye laser

We demonstrate the versatile operation of a linear femtosecond dye laser that terminates in an antiresonant ring for passive colliding-pulse mode locking. The system combines several advantages of a conventional ring laser with those of a linear laser and in addition offers the unique possibility of continuously tuning the pulse-repetition rate over a 1-GHz band. Moreover, the geometry allows a commercial linear laser to be mode locked easily without significant cavity changes.