Analysis of a mode-locked ring laser: chirped-solitary-pulse solutions

Abstract

We present measurements on mode-locked ring dye lasers that demonstrate the role of self-phase modulation in the saturable absorber dye. The resulting bandwidth increase plays an essential role in ultrashort pulse generation, because it leads to intracavity pulse compression in the presence of normally dispersive components. The role of various intracavity components (glass, coatings) in intracavity compression is analyzed. As opposed to extracavity compression, measurements of pulse amplitude and phase show that the nonlinear phase modulation can be completely compensated. The interaction of the light pulse with the absorber is analyzed using Maxwell–Bloch equations. Next, we find the steady-state solution for the problem of pulse propagation through an infinite periodic medium containing all the essential intracavity elements (bandwidth-limiting filter, amplifier, absorber, dispersive component). The condition that the solitary pulses be unchirped enables us to determine the optimum intracavity dispersion, which, in agreement with the experimental data, leads to the shortest pulses.