We report on the development and manufacturing of two different types of high-dispersive mirrors (HDM). One of them provides a record value for the group delay dispersion (GDD) of -4000 fs2 and covers the wavelength range of 1027-1033 nm, whereas the other one provides -3000 fs2 over the wavelength range of 1020-1040 nm. Both of the fabricated mirrors exhibit a reflectance of >99.9% and are well suited for intracavity applications. Mirrors of the second type have been successfully employed in a Kerr-lens mode-locked Yb:YAG thin-disk oscillator for the generation of 200-fs pulses with multi-10-W average power.
Nowadays, dispersive mirrors are able to cover the wavelength range of 4.5 optical octaves and can be used from 220 nm up to 4500 nm. Various design approaches to dispersive mirrors in visible and near IR are briefly discussed. We consider in more detail two dispersive mirrors representing extreme cases. The first one is a mirror working in the range of 290−360 nm and providing group delay dispersion of -75 fs 2 . The second one is a mirror working in the range of 2500−4500 nm and providing +500 fs 2 of group delay dispersion.
Multilayer coatings composed of TiO 2 , Ta 2 O 5 , HfO 2 , or Al 2 O 3 as high-index materials and SiO 2 as low-index material were investigated for laser-induced damage using 1 ps, 5 µJ pulses generated by a mode-locked Yb:YAG thin-disk oscillator operating at a wavelength of 1030 nm and repetition rate of 11.5 MHz. Previously reported linear band gap dependence of damage threshold at kHz repetition rates was confirmed also for the MHz regime. Additionally, we studied the effect of electric field distribution inside of the layer stack. We did not observe any significant influence of thermal effects on the laser-induced damage threshold in this regime.
We studied e-beam evaporated TiO2 films deposited at two different substrate temperatures between 120°C and 300°C. We reliably characterized the film samples on the basis of in situ and ex situ measurements. We carried out annealing on the samples and studied the induced changes in the properties of the films. The results can be useful for further laser-induced damage threshold investigations.
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