Investigation of Passively Mode Locking Condition for a CW Dye Laser

We have investigated the operational parameters of a passively mode-locked Rh-6G dye laser, having a cavity with five mirrors and two jet streams, in order to generate stable subpicosecond pulses. The optimum concentration of saturable absorber (DODCI) was found to be 6.0×10-6M. The ratio of pumping power Pp to the threshold power Pth (Pp/Pth) falls in a range of 1.08±0.01, in order to obtain good mode-locking. The optimum value Pp/Pth is independent of the DODCI concentrations. Under this optimum condition, the narrowest pulses of 0.69ps were generated at 614nm. The time-bandwidth product of the pulse was calculated to be 0.78 indicating that the pulse was close to being transform-limited. The lasing-wavelength was tunable in the range of 604-613nm by using a Lyot filter. A nearly transform-limited pulse of 1.54ps with the time-bandwidth product of 0.40was obtained at 605.5nm.