We present the experimental investigations on the filament characteristics of sharply focused fs pulses (800 nm, 45 fs, 1
kHz) in air. Pulses with input powers in 3-12.2 PCr range were focused using three different focusing geometries f/#10,
f/#15 and f/#20 corresponding to numerical apertures (NA) of 0.05, 0.033 and 0.025, respectively. The dynamics of
filaments were observed via direct imaging of the entire reaction zone. The length of the filament has decreased with
increasing NA from 0.025 to 0.05, while, the filament width has increased. For a given focusing geometry, the filament
length and width increased with increasing power. However with higher NA, the length and width were observed to
saturate at higher input powers. With the highest NA of 0.05 and higher input powers used in the current study, the
presence of coherently interacting multiple filaments either resulting in a fusion or exchange of power.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.