Abstract

The second-harmonic nonlinear mirror, consisting of a frequency-doubling crystal and a mirror totally reflecting the second-harmonic wave, can be used as a passive mode-locker, substituting for conventional saturable absorbers.^1,2 The nonlinear reflection of ultrashort pulses by this device is affected only by the group- velocity mismatch; the limit can be roughly estimated from the crystal length and groupvelocity dispersion data. An important parameter of the nonlinear mirror used as a mode-locker is the pulse shortening in a single pass. This was analyzed for quasi-stationary second- harmonic generation,³ assuming that all frequency components are perfectly phase-matched. With respect to femtosecond-pulse generation from mode-locked lasers, the ultimate pulse-shortening capabilities of the nonlinear mirror are of great interest.

© 1991 Optical Society of America