High Energy diode-pumped femtosecond oscillator with 1 μJ pulse energy at 9 MHz pulse repetition rate

High energy femtosecond oscillators at high pulse repetition rate have a great potential for many applications such as micro- and nano-machining and structuring, waveguide writing in dielectric media, or nonlinear frequency conversion. Up to now most femtosecond oscillators operating at pulse repetition rates higher than 1 MHz were limited at pulse energies of typically a few tens of nanoJoules. We demonstrate a directly diode-pumped Yb:KYW laser oscillator delivering pulse energies up to 1 mu J and pulse durations down to 430 fs, thus pulse peak powers exceeding the MW level. The pulse repetition rate is 9 MHz and the average power is on the 10-W-level. The laser setup is compact and fits in a 60 x 40 cm footprint. We externally compressed the pulse duration of this laser down to about 60fs by focusing the laser into a large mode area micro-structured fiber followed by a compressor module containing a pair of parallel aligned dispersive mirrors. The good coupling efficiency and the high-reflecting dispersive mirrors resulted in an overall compressor transmission of 80%. For a maximum injected pulse energy of 0.53 mu J we obtained up to 0.42 mu J pulse energy after the compressor which corresponds to a peak power of 7 MW.