3 MHz Amplifier for Femtosecond Optical Pulses

Abstract

We describe a system designed specifically for amplification of femtosecond optical pulses [1,2] at high (3 MHz) repetition rate. A key problem in high repetition rate amplification is that the energy of the available pump pulses is only a few microjoules as compared to the hundreds of millijoules available for low repetition rate amplifiers [2]. We resolve this problem, in part, by using multiple collinear passes to extract efficiently the pump pulse energy while also maintaining the transverse coherence and femtosecond duration of the amplified pulse. In addition we have for the first time cavity dumped the source laser, a colliding pulse mode-locked ring laser [3] while maintaining the femtosecond pulse duration. The pulse energy incident on the 3 MHz amplifier has thereby been increased by an order of magnitude, thus reducing the amplification requirements. Our amplifier, like previous high repetition rate amplifiers [4,5], employs a cavity dumped argon ion laser as the pump. The unique features of our system are the amplification of femtosecond, rather than picosecond, pulses and the use of an exactly collinear pumping geometry.