Femtosecond pulse generation in a linear passive mode-locked dye laser

The femtosecond pulse generation in a c.w. pumped linear passive mode-locked rhodamine 6G-DODCI (3,3-diethyloxadicarbo cyanine iodide) dye laser is studied experimentally. Colliding pulse mode-locking (CPM) is achieved by placing the saturable absorber jet in the centre of the linear ring resonator. The laser performance is studied as a function of the saturable absorber concentration and of the absorber jet detuning from the central position (CPM position). Without a prism pair in the resonator pulse durations down to 140 fs were obtained. Detuning the absorber jet from the CPM position resulted in a trailing pulse tail ofcirca 900 fs duration. The dependence of the laser performance on the prism pair positioning is investigated experimentally and analysed theoretically. At the prism pair balanced position, stable pulses of about 50 fs duration were generated independent of the lateral detuning of the absorber jet out of the resonator centre. The dependence of the laser wavelength on the absorber concentration is compared with theoretical predictions. In an appendix the ray-tracing inside the linear resonator is simulated by an ABCD matrix calculation for Gaussian beams.