High energy pulse self-compression in a hollow core waveguide filled with noble gases has been under intensive study. Here, its dependence on the input pulse group delay dispersion (GDD) and third order dispersion (TOD) is studied experimentally. Pulses with energy of 3 mJ, at a repetition rate of 1 kHz, with Fourier transform limited FWHM pulse duration of 24 fs from a Ti:sapphire laser amplifier system are focused into a 2 cm long, 150 μm inner diameter hollow core waveguide filled with 10 mbar argon gas for self-compression. The input pulse GDD and TOD are tuned by an acousto-optic programmable dispersive filter in the laser amplifier system and the output pulses after the waveguide are measured. We found that the pulses are optimally compressed along a diagonal line in the GDD-TOD plane, where the output pulses are near Fourier transform limited. However, along the other diagonal line the pulses are poorly compressed due to pre-pulses appearing. We also compared the spectral phases and temporal profiles of the output pulses at selected points along the two diagonal lines. Along the optimal compression diagonal line, the spectral phases are flatter and the temporal profiles are better comparing to the other diagonal line where the strong pre-pulses occur. Therefore, the optimal input pulse shapes for self-compression are those without pre-pulses. These input pulses can be found easily along the diagonal line where the GDD is decreasing with the TOD in the GDD-TOD plane.
|