Negative Dispersion Mirrors in Ta₂O₅SiO₂ for Femtosecond Ti:Sapphire Lasers by Using Gires--Tournois Interferometers

We design and experimentally demonstrate some negative dispersion mirrors with optimized Gires--Tournois interferometers. The mirror structure is composed of 38 alternating Ta₂O₅ and SiO₂ layers and could be regarded as two sections: high-reflectivity section consisting of a series of quarter-wavelength optical thickness stacks and negative-dispersion section consisting of only 13 layers. The designed mirrors exhibit the expected performance. These mirrors were fabricated by using ion beam sputtering. By adopting such mirrors, dispersion of a mode-locked femtosecond Ti:sapphire laser has been compensated for mostly. With two series of the mirrors, 32fs and 15fs pulses have been obtained respectively.