Peter Rußbüldt

Transverse mode tailoring in a quasi-imaging high-finesse femtosecond enhancement cavity

We demonstrate a high-finesse femtosecond enhancement cavity with an on-axis obstacle. By inserting a wire with a width of 5% of the fundamental mode diameter, the finesse of F = 3400 is only slightly reduced to F = 3000. The low loss is due to the degeneracy of transverse modes, which allows for exciting a circulating field distribution avoiding the obstacle. We call this condition quasi-imaging. The concept could be used for output coupling of intracavity-generated higher-order harmonics through an on-axis opening in one of the cavity mirrors.

Tailored transverse modes in high-finesse femtosecond enhancement cavities

Degenerate transverse modes are used to excite a field distribution with maximum on axis intensity near the focus and avoiding a large on-axis aperture far away from the focus in a femtosecond resonator with finesse 3000.

Power scaling of ytterbium INNOSLAB amplifiers beyond 100W average power

The Innoslab design, already established for neodymium doped laser materials, was applied to ytterbium doped laser materials. Recent progresses in brightness of high power diode lasers facilitate efficient pumping of quasi-three-level laser materials. A compact diode-pumped Yb:YAG Innoslab fs-oscillator-amplifier system, scalable to the kilowatt range, was realized. Nearly transform and diffraction limited 682 fs pulses at 400W average output power and 76 MHz repetition rate at room temperature and without using CPA technique have been achieved so far.

Direct low-harmonic generation in gas at MHz repetition rate

High harmonic generation (HHG) at multi-megahertz pulse repetition rates is challenging, since pulse energy is several orders of magnitudes lower for such lasers than for those conventionally used for the HHG: micro-joules instead of milli-joules. However we have observed the 5th and 7th harmonic (till approx. 17 eV) with 5 μJ pulses at 50 MHz repetition rate with frequency doubled Yb:YAG Innoslab amplifier. The single-pass HHG with the Innoslab amplifier at 20.8 MHz repetition rate was demonstrated [1]. For these experiments the nonlinear pulse compression was implemented.

Compact high Power Ytterbium based fs-Oscillator-Amplifier System

A compact diode-pumped Yb:YAG Innoslab fs-oscillator-amplifier system, scalable to several 100W, was realized. Nearly transform and diffraction limited 786fs pulses at 77W average output power and 63.2MHz repetition rate are achieved so far.