Two-dimensional high resolution electron properties of femtosecond laser-induced plasma filament in atmospheric pressure argon

This work reports the measurement of two-dimensional electron properties over a nanosecond scale integration time across a femtosecond laser-induced plasma filament in atmospheric pressure argon. Radial electron properties across the $$\sim 100$$∼ 100 $$\upmu$$μ m diameter filament are obtained at discrete axial locations at 2.5 mm steps by one-dimensional high-resolution laser Thomson scattering with a spatial resolution of 10 $$\upmu$$μ m. These measurements reveal plasma structural information in the filament. The Thomson spectral lineshapes exhibit clear spectral sidebands with an $$\alpha$$α parameter $$\sim 1$$∼ 1 , enabling the measurement of both electron temperature and density profiles. These measurements yield electron densities on the order of $$10^{22}$$10 22 /m $$^{3}$$3 and electron temperatures of $$\sim 2$$∼ 2 eV. Heating from the probe laser due to inverse bremsstrahlung is taken into account to correct the Thomson scattering electron temperature measurements. Under these conditions, electron-neutral collision induced bremsstrahlung becomes the dominant laser-induced plasma heating process associated with the probe laser. The measurements reveal structural features of the filament, including an asymmetrically skewed density structure in the axial direction and reversed radial distributions of electron density and temperature.