Generation of controlled-duration ultrashort pulses in a passively mode-locked YAG:Nd3+ laser

The results are given of an investigation of a simple method for generating controlled-duration ultrashort pulses in a YAG:Nd³⁺ laser, passively mode-locked by a nonlinear filter with saturable absorption. The physical basis of the duration control is a variable initial transmission of the filter and the predominance of the action of temporal pulse compression by the nonlinear filter over the pulse broadening factor during the linear amplification stage in the active medium and corresponding spectral narrowing. The technical realization of the method of controlling the duration of ultrashort pulses is based on the use of a polymer switch utilizing dye №4363, an analog of №3274, and made in the form of a wedge. A service life was achieved in which ~10⁴ pulses were generated at a single point in the switch when the pulsetrain energy was ~2 mJ. The range in which the duration of ultrashort pulses from the YAG:Nd³⁺ laser could be controlled was 15–100 psec, with practically 100% reproducibility of lasing of a single pulse per axial period. The 100% probability of isolating a single ultrashort pulse per period was due to the mode self-locking in the free-lasing regime.