With the advent of high-intensity short pulse lasers it has become possible to achieve extremely high intensities. When such laser pulses interact with plasmas or high-energy electron beams, radiation damping, which is usually small, can become large. We examine the effects of radiation damping on the backscattered Thomson radiation numerically and analytically. Using parameters comparable to the laser and microtron at the Advanced Photon Research Center we find that the overall spectrum is down-shifted and that the overall amplitude of the radiation is smaller than in the case with no damping.

We observed a preformed plasma of an aluminum slab target produced by a high-intensity Ti:sapphire laser. The expansion length of the preformed plasma at the electron density of 3 × 1018 cm−3, which was the detection limit, was around 100 μm measured with a laser interferometer. In order to characterize quantitatively and to control the preformed plasmas, we perform a two-dimensional hydrodynamic simulation. The expansion length of the preformed plasma was almost the same as the experimental result, if we assumed that the amplified spontaneous emission lasted 3.5 ns before the main pulse arrived.