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This work deals with the investigation of the optical properties of epitaxial YAG : Yb films and their suitability as gain media for thin disk lasers. Epitaxial films of YAG : Yb were grown by the liquid phase epitaxy method in air on the (111)-oriented YAG substrates. The thickness of the grown layers was from 30 to 260 µm. The melt composition was varied to obtain the desired doping level from 10 to 15% and to optimize the optical properties. The best epitaxial films were colourless and had an Yb 3+ luminescence lifetime of more than 950 µs, which is very close to the intrinsic lifetime of the Yb ions in the bulk YAG single crystals. These films were tested in a thin disk laser setup with 24 absorption passes of the 940 nm pumping beam. The maximum output power at 1.03 µm wavelength in CW operation reached more than 60 W and the optical efficiency was close to 30%.

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A method for obtaining very high electro-optic switching rates is demonstrated and employed for regenerative amplification of ultrashort pulses at high repetition rates. The intracavity polarization switch consists of a transverse-field BBO Pockels cell and a dielectric thin film polarizer. By multiple-shift usage of a single BBO crystal as Pockels cell, it is possible to keep thermal dissipation losses in the Pockels cell driver below 200 W. Using this intracavity polarization switch in an ultrafast thin-disk Yb:KYW regenerative amplifier, pulse energies of about 9 μJ with pulse durations of 280 fs at repetition rates of 200 kHz were generated.