Ultrashort compression of amplified optical pulses

Abstract

We have developed an amplifier for femtosecond optical pulses that is pumped by the frequency-doubled output of a mode-locked Nd:YAG laser Q-switched at 800 Hz. We have successfully used this type of system to amplify both 100-fs output pulses from a colliding pulse mode-locked ring dye laser and 200-fs pulses obtained by compression of the output of a synchronously pumped, cavity pumped dye laser. In both cases, synchronization of the YAG laser pulses with the pulses from the dye laser is achieved by driving its acoustooptic mode-locker with a rf signal phase-locked to the optical pulse train of the dye laser. A short-term jitter of <25 ps is observed with this technique. A two-stage configuration allows amplification up to the microjoule level. We also have successfully addressed the problem of amplification of compressed optical pulses. Our primary application for this system is pulse compression in an optical fiber. The excellent mode quality of the amplified beam allows a coupling efficiency into the 4-μm fiber core of over 60%. Furthermore the very good amplitude stability enables us to obtain the highest compression ratios ever achieved on the femtosecond time scale (110 fs to 12 fs and 200 fs to 16 fs with the two systems, respectively).