Terahertz white-light pulses from an air plasma photo-induced by incommensurate two-color optical fields

We demonstrate plasma-THz generation in ambient air with two-color (omega-2 omega) optical excitation using input pulses with a bandwidth supporting sub-20-fs duration, yielding a continuous bandwidth exceeding 100 THz with no significant roll-off and a pulse energy of 360 nJ at a 1-kHz repetition rate. The key aspect in achieving this performance is an optimized geometry of the second-harmonic generation (SHG) crystal, producing a 2 omega-field detuned from the second-harmonic of the omega-field, which promotes both a high polarization bandwidth and optimal omega-2 omega temporal overlap in the plasma, as supported by theoretical results. (C) 2010 Optical Society of America