A new regime of laser filamentation is demonstrated with terawatt, picosecond CO2 laser pulses forming a single centimeter diameter channel in air. Joules of pulse energy are self-guided at a clamped intensity of ~1012 W/cm2 due to generation of free carriers via many-body Coulomb effects.
An array of synchronized microphones measures energy deposition along the length of laser filament in a single shot. A spread of collapse location positions due to air turbulence and laser energy fluctuations causes a pronounced difference between single shot measurements and conventional multi-shot averaging.
We present time- and frequency-resolved measurements of self-focusing and self-defocusing of 4.3-4.8 µm Fe:ZnSe laser pulses tuned near rovibrational transitions of CO2 And CO. We estimate the resonant nonlinearity of the air at 4.3 µm and discuss the novel nonlinear optics of simple molecules.