Impact of gas dynamics on laser filamentation THz sources at high repetition rates

We experimentally demonstrate that the terahertz (THz) emission from two-color laser filaments in gases is strongly affected by the pulse repetition rate of the driving laser. We show that at repetition rates above 100 Hz, propagation of every next laser pulse in the pulse train is altered by gas density depressions produced by the preceding laser pulses. As a result, plasma channels at higher repetition rates become shorter, leading to less efficient THz generation. In particular, we observe a 50% decrease in the emitted THz energy when the repetition rate increases from 6 Hz to 6 kHz.