Pulse Structure Studies and Absolute Cavity Length Determination for a Synchronously Pumped Picosecond Dye Laser

Second harmonic cross correlation functions of a pulse with its near neighbor have been studied in a synchronously pumped cw dye laser. Measurements were made both as a function of dye laser cavity length mismatch and the number of cavity round trips separating the correlated pulses. The pulse envelope is found to have a characteristic interpulse frequency determined by the pump laser, whereas the pulse substructure has a characteristic frequency determined by the dye laser cavity length. The cross correlation measurements allow experimental determination of the dye laser length corresponding to exact synchrony. In contrast to theoretical predictions the length of exact synchrony corresponds to optimum pulse shape and duration. Our results are discussed in terms of a simple model which leads to pulse duration estimates as much as twice those obtained by conventional analysis of autocorrelation traces.