Abstract

Pulses from two mode-locked lasers have been synchronized to better than 2 ps. The technique, similar to that used by Halbout and Grischkowsky¹ uses the output of a passively mode-locked CPM dye laser to generate a radiofrequency (rf) signal which can be used to drive a mode-locker for a second laser. In our case, the second laser is a diode pumped Nd:YLF (DPY) FM mode-locked with a lithium-niobate phase modulator.² FM mode-locking has two advantages over AM mode-locking: it does not require a rf divide by two element, and the phase modulator tank circuit can be easily tuned without reducing its Q. The tank circuit has a relatively low Q that allows the DPY laser to be adjusted to the CPM laser frequency without tuning the circuit. The CPM can be set optimally to produce the shortest pulses, and the DPY adjusted to operate in synchrony. The DPY generates pulses as short as 15 ps at 100 Mhz; it operates stably in two modes corresponding to pulse durations of 15 and 30 ps. The shortest pulses, measured by a cross correlation with pulses from the CPM, are neither Gaussian nor hyperbolic secant in shape. They have an asymmetric shape with one or two satellite pulses preceding or following the main pulse depending on the cavity length detuning.

© 1991 Optical Society of America