Specific features of laser pulse amplification in double-pass single-stage amplifiers

Theoretical and experimental investigations of double-pass single-stage amplifiers are reported. A two-level approximation is used to derive analytic expressions for the gain in two important cases, with and without (ultrashort pulses) complete temporal overlap of the pulses. It is shown that, for small input signals, a 20% improvement in the ultrashort pulse gain can be achieved.