Energy Deposition of Single Femtosecond Filaments in the Atmosphere

We present spatially resolved measurements of energy deposition into atmospheric air by femtosecond laser filaments. Single filaments formed with varying laser pulse energy and pulsewidth were examined using longitudinal interferometry, sonographic probing, and direct energy loss measurements. We measure peak and average energy absorption of ∼4 μJ/cm∼4 μJ/cm and ∼1 μJ/cm∼1 μJ/cm for input pulse powers up to ∼6∼6 times the critical power for self-focusing.