We report the implementation and operation of novel superhigh-reflectivity negative-dispersion dielectric mirrors for use in tunable ultrafast laser systems. The mirror structure is divided into two distinct regions: an underlying superhigh-reflectivity dielectric quarter-wavelength stack and an overlying negative-dispersion section consisting of only a few layers and forming simple multiple Gires-Tournois interferometers. The example that we present was designed for operation from 800 to 900 nm and has a near-constant group-delay dispersion of -40 fs(2) and a peak reflectivity greater than 99.99%. We show a comparison of the predicted and the measured mirror performance and application of these mirrors in a mode-locked Ti:sapphire laser tunable from 805 to 915 nm.
The dependence of a single-shot laser-induced damage on certain film properties is investigated. Variable stress films are produced by mixing pure components with imilar damage thresholds; a definite stress dependence is shown. Films formed from mixtures of high and low threshold components are investigated and found to have damage thresholds between the high and low component values. The damage thresholds of multilayer and periodic inhomogeneous film systems are compared. The results confirm that the damage threshold is almost entirely material-dependent and equal to the threshold of the lowest threshold component for highly reflecting multilayers. Multilayers deposited at different vapor incidence angles are compared. A definite dependence is shown.
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