Nonlinear stage of ultrashort-pulse formation in solid-state laser

Formation of ultrashort pulses in a YAG:Nd(3+) laser is considered, particularly in nonlinear stage. The dependence of the resulting pulse duration on the length of this stage as well as on the length of the free-emission stage and on the density of a passive shutter is evaluated on the basis of experimental data and computer-aided numerical analysis of the applicable theoretical relation. Results reveal that it is possible to decrease the duration of ultrashort pulses by lengthening the nonlinear stage and shortening the linear one, under two-threshold condition, and that sufficient lengthening of the nonlinear stage will eventually saturate the shutter effect. Lowering the density of some shutters such as 4050 film in polymethyl methacrylate was found to decrease the pulse duration, while lowering the density of others such as 3274 dye in acetone solution increases it.