Octave-spanning spectra directly from a two-foci Ti:sapphire laser with enhanced self-phase modulation

Summary form only given. The generation of spectra extending over one octave directly from a laser oscillator is challenging in many aspects. First of all, the limited gain bandwidth of the laser material, about 200 nm in the case of Ti:sapphire, has to be overcome by nonlinear spectral broadening (SB) via self phase modulation (SPM). The amount of SPM and hence the SB per roundtrip is determined by the available intracavity pulse energy, which is limited by optimum Kerr lens mode-locking (KLM) action. Second, one has to provide a high mirror reflectivity and well controlled dispersion properties over the whole desired spectral range. Recent efforts in this field provided pulses in the two-cycle regime with bandwidths below one octave. In our work we refined the intracavity approach by adding a second intracavity focus. Together with specially designed double-chirped mirror pairs, we obtained the broadest spectrum ever generated directly by a laser and successfully recompressed the pulses to 5 fs.