Design and implementation of a TW-class high-average power laser system

We describe the design, modeling and characterization of a titanium-doped sapphire multipass, kilohertz amplifier system with output pulses of energy 4.4 mJ and duration 17 fs, giving a peak power of 0.26 TW. The thermal lensing in the second amplifier stage is virtually eliminated by cryogenic cooling of the laser crystal. Gain-narrowing and shifting of the amplified spectrum are reduced by tailoring the output spectrum of the oscillator and by using a low-loss multipass amplifier chain. Fourth-order spectral dispersion was completely eliminated by using a prism pair in addition to adjusting the stretcher and compressor grating separation and angle. We also numerically modeled the evolution of the pulse energy and spectral phase and amplitude through the amplifier system. The results of the model are in excellent agreement with measurements made using the technique of transient-grating frequency-resolved optical gating.