Abstract

We describe a multipass optical amplifier based on a double confocal geometry¹ which we have used to amplify femtosecond optical pulses to energies of 90 nJ using only 0.7 W of pump power from a Metalaser copper vapor laser operated at 10 kHz. We use four mirrors of 20-cm radius arranged so that an incident train of pulses passes six times through a gain jet containing a mixture of rhodamine 640 and sulforhodamine 640 in ethylene glycol. The amplified pulses, which have durations of ~50 fs, are sufficiently intense to generate white light continuum pulses in an optical fiber with a 4-μm core.

© 1988 Optical Society of America