Pulse repetition rate effect on the plasma inside femtosecond laser filament in air

Figure 1. Experimental setupFigure 2. The typical spectrum of the O I generated by the laser filament. (a) Multi-Voigt fit for the O I 777.194, 777.417, and 777.539 nm lines was performed to determine the stark broadening of the plasma. (b) Multi-Voigt fit for the O I 844.626, 844.636, and 844.676 nm lines. The six spectral lines of the O I were used to plot Boltzmann plot and determine the temperature of the plasma. The laser pulse energy was 4.5 mJ for filamentation.Figure 3. (a) Simulated average electron density of the filament as a function of propagation distance for 1, 100, 500 and 1000 Hz repetition rates. The electron density is averaged in the range of  (the radius of the filament) (b) The electron density of the laser filament as a function of the laser repetition rate. The red line is the simulated average electron density of the filament zone. The filament zone is defined by specifying the filamentation initiation and termination when the electron density approaches .Figure 4. (a) the Boltzmann plots for O I from 100 Hz and 1000 Hz filaments. (b) the plasma temperature as a function of the laser repetition rate. The red line in (b) the simulated laser intensity inside the filament for comparation. The laser pulse energy was 4.5 mJ for filamentation.