Timing Fluctuations Due to Beam Steering in Prism-Compensated Kerr-Lens Mode-Locked Lasers

Variation in the round-trip group delay through an intracavity prism pair is studied as a function of index variation in the gain medium. The resulting sensitivity to index perturbation gives insight into the degree to which pump noise will transfer to timing instability through this mechanism. General expressions for group-delay time change and slope are derived. It is found that thermal and nonlinear index changes in the gain crystal result in group-delay time sensitivities of 4.34 × 10^-17 s/K and 1.25 × 10^{- 26} s·cm²/W, respectively, for a conventional 100-MHz Kerr-lens mode-locked laser. For a nominal temperature fluctuation of 1 K and a peak intensity variation of 5 × 10⁸ W/m², this implies round-trip timing variation of 5 × 10^-17 s, which is very small, but not insignificant in today´s clock technology.