Time-resolved measurements of cumulative effects in gas dynamics induced by high-repetition-rate femtosecond laser filamentation

Abstract

The advent of high-average-power, ultrafast ytterbium-based lasers allows us to generate laser filaments at repetition rates ranging from tens of kHz up to hundreds of kHz. At such high-repetition rates, the inter-pulse time lies below the time required for the total diffusion of the deposited heat by each laser pulse, leading to cumulative hydrodynamic effects. Here, we present experimental time-resolved measurements of these dynamics in air for laser repetition rates between 1 and 100 kHz. We measure the change in the air refractive index caused by the localized heat deposition and the length of the filament-generated plasma channel, with which we can infer the corresponding change in air density. We observe that at repetition rates above 10 kHz, stationary density depletions with vanishing dynamics emerge. Our findings are of wide relevance for the fields of high-repetition-rate laser filamentation and its applications as well as THz generation from laser-induced plasma sources.