Optimization of few-cycle pulse generation: spatial size, mode quality and focal volume effects in filamentation...

We demonstrate the key role played by the spatial characteristics and focusing conditions of a femtosecond multi-cycle laser pulse in optimization of filament output for the purpose of obtaining compressed light pulses in the few-cycle regime. We find that for a given beam profile and focal parameters, driving the filament with energy above a certain limiting value can negatively impact pulse compression. However, for a given energy, a smaller and cleaner input beam mode obtained by using a hard aperture can substantially improve the pulse compression ability. In addition, we show that a larger focal volume can assist in creation of a shorter output pulse.