Mode locking of an active multipass geometry

Ultrashort laser pulses in the microjoule regime are of prime importance for many applications. Previous record pulse energies obtained directly from an oscillator in ambient atmosphere were below 2 μJ. This thesis describes a newly developed thin-disk laser oscillator with an increased round-trip gain by employing a self-imaging active multipass geometry. The generation of high energy subpicosecond pulses with a pulse energy of up to 25.9 μJ at a pulse duration of 928 fs, while operated in ambient atmosphere, could be demonstrated. Stable single-pulse operation has been obtained with an average output power in excess of 76W at a repetition rate of 2.93MHz. Self starting passive modelocking was accomplished using a semiconductor saturable absorber mirror (SESAM) with a modulation depth of 3.5%%. The laser was operated at output-coupling rates of up to 78%%.