Efficient energy extraction below the saturation fluence in a low-gain low-loss regenerative chirped-pulse amplifier

Simulations of chirped-pulse amplification (CPA) in a quasi-three-level laser are presented which illustrate how depletion of the inversion can occur at ten times below the saturation fluence in a regenerative amplifier. The simulations are applied to Yb:glass, a promising laser medium for a directly diode-pumped high-peak power laser. Virtually stretching a pulse to a portion of the buildup time of a regenerative amplifier allows for efficient energy extraction from a laser medium that has a saturation fluence greater than the damage threshold. Experimental results from a Yb:glass regenerative amplifier produced 12-mJ pulses at a peak fluence of 9 J/cm/sup 2/ without damage.