Mechanisms of spectral shift in ultrashort-pulse laser oscillators

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 (similar to 25 nm), whereas the high-order dispersion contribution is insignificant (similar to5 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. (C) 2001 Optical Society of America.