Mechanisms of spectral shift in ultrashort-pulse laser oscillators

Abstract

A number of factors that influence spectral position of ultrashort pulses in mode-locked lasers have been identified: high-order dispersion, gain saturation, reabsorption from the ground state, and stimulated Raman scattering. Using the one-dimensional numerical model for the simulation of the laser cavity, we analyze the relative contributions of different factors to the spectral position of the mode-locked pulses using the example of the Cr:LiSGaF laser. In this case the Raman effect provides the largest self-frequency shift from the gain peak (up to 60 nm), followed by the gain saturation (;25 nm), whereas the high-order dispersion contribution is insignificant (;5 nm). The results of the simulation are in good agreement with experimental data, confirming that stimulated Raman scattering is the dominant mechanism that causes the pulse self-frequency shift. © 2001 Optical Society of America OCIS codes: 140.3580, 320.5550, 320.2250.