Fourier transform method for self-mixing interference signal analysis

Cr4+ : YAG crystal was used as a saturable absorber in an active-passive mode-locked Nd : YAG laser. The stable and complete mode-locked pulse train was achieved at 1064 nm. The duration of a single pulse was obtained from 0.8 to 2.4 ns by changing the Cr4+ : YAG crystal with different initial transmission, when there was the shortest pulse width. The mode-locking dynamic process of Cr4+ : YAG crystal was analyzed by the rate equations to explain the experimental result, and the effect of excited-state absorption was considered.