Propagation of Intense Subpicosecond Laser Pulses through Underdense Plasmas

The propagation of an intense, subpicosecond laser pulse through a substantial length $(L/\lambda \sim {10}^3)$ of an underdense plasma $\left({n/n}_c\sim 1\%\right)$ is studied through experiments and computer simulations. For $I=8\mathrm{}\times {10}^{17}$ W/c${\mathrm{m}}^2$ only 55% of the incident laser light was transmitted through the plasma within the focal cone angle. The decrease in transmission was accompanied by Raman forward scattering as evidenced by the generation of anti-Stokes sidebands and up to 2 MeV electrons. Simulations show that the majority of the reduction in transmission could be due to Raman forward and side scattering.