Design of Gires-Tournois Interferometer Mirror Used in Cr:LiSAF Femtosecond Lasers

An useful design used for the dispersion compensation in Cr:LiSAF femtosecond lasers is reported. It is composed of 58 alternating Ta2O5 and SiO2 layers. The first part, from layer 1 to layer 45, which have quarter-wave optical thickness serve as high reflectivity dielectric stack. The second part, from layer 46 to layer 58, whose thicknesses are obtained by computer optimization provide constant negative group delay dispersion. The optimized GTI mirror exhibits continuous high reflectivity of greater than 99.9% and nearly constant group delay dispersion of -35fs2 from 750nm to 900nm. After four bounces, the designed GTI mirror can compensate most group delay dispersion of 3-mm Cr:LiSAF crystal per round trip.