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Negative Dispersion Mirrors in Ta2O5/SiO2 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, 32 fs and 15 fs pulses have been obtained respectively.