Optical and Quantum Electronics 16 (1984) 393-398 The time-resolved spectrum of a pulsed dye laser J. O. TOCHO, H. F. RANEA-SANDOVAL, R. DUCHOWICZ, M. GARAVAGLIA Centro de Investigaciones Opticas, (CONICET-UNLP-ClC), PO Box 124, 1900- La Plata, Argentina Received 1 December 1983 The spectral evolution in a xenon ion-pumped open dye stream laser was measured and analysed in terms of a theoretical spectro-temporal relation previously derived. Sweep occurs in a 200 ns time scale and simultaneous oscillations of several wavelengths can be achieved by varying laser cavity parameters. Experiments were completely reproduced by assuming that the phenomena can be ascribed to the homo- geneous broadening of the laser fluorescent band. 1. Introduction Pulsed dye lasers are known to have a broad emission band. With different dyes and pumping conditions, it can be 2-20 nm [1 ] wide. The peak of the band is changed by several factors, e.g. solvation effects, dye solution concentration, pH and laser cavity Q [2]. It is well known [3] that, in the time dcmain, the time at which the intensity at any wavelength reaches its maximum depends on the wavelength; the inte- gration of this spectral evolution results in the broadband emission of these substances. Several exper- iments were performed in the early days of dye lasers to investigate this phenomenon. In an early experiment [3], a Q-switched ruby laser of 20 ns pulse duration longitudinally excited a dye cell, and after spectral discrimination, the observation was made with a fast photodiode. Soon after, in similar experiments [1, 4], a streak camera 'crossed' with a spectrograph was used as spectro-temporal analyser. The results show that the long wavelengths in the dye laser spectrum peak later than the short ones do. In one of them [4] the emission starts on the blue side of the fluorescent band, sweeps with time towards the red and reach some maximum wavelength; then the sweep reverses and moves back to the blue. In this case the streak showed a 'hooked' appearance. Later experiments performed with flashlamp-excited dye lasers with typically 1/as pulse duration [2], also found a red sweep but not the blue-reversal expected in previous theoretical treatments [5]. Similar results were obtained more recently with a jet-stream dye laser pumped by a cavity-dumped argon ion laser [6] with variable pulse duration from 20 to 200 ns. This phenomenon was attributed to a variety of reasons: inhomogeneous broadening [3], time- dependent triplet losses [4], thermal effects, spatial hole-burning [6], and it was theoretically proposed to ascribe it to the homogeneous broadening of the fluorescent band which led to an intrinsic time re- distribution of photon population of the cavity modes [7, 8]. In this paper we report the study of the spectro-temporal behaviour of a xenon ion laser-excited open jet-stream dye laser. The experiment measuring the effect is described in Section 2. Two sets of results corresponding to different Q for the dye laser cavity are given in Section 3. In Section 4, the results are examined with a simple model due to Meyer and Flamant [7]. Section 5 is a discussion of results and theory. 2. Experiment A jet-stream dye laser was excited by a pulsed Xe ion laser and the spectral emission was analysed by a 0306-8916/84 $03.00 + .12 9 1984 Chapman and Hall Ltd. 393