Interferometry of laser plasma density distribution at superfilamentation regime in ambient air

Plasma density spatial distribution at superfilamentation regime of femtosecond laser radiation in ambient air was measured by precision interferometry technique. It was shown that at weak focusing (f-number ~125) the filaments formed before the focus converged near the focus and formed superfilament without changing the plasma density while at stronger focusing (f-number ~50) the plasma density in each filament increased several times.