ИСТИНА

Plasma created by femtosecond laser pulse of high intensity can be used as the brilliant source of high energy electrons, ions and X- or -rays. In most cases, laser pulses with high contrast are used for particle acceleration. In this work we present results of the experimental and numerical studies of gammaproduction in slightly relativistic regime. We exploited different target types (flat, nanostructured, liquid) and various pre-pulses (femtosecond and nanosecond artificial pre-pulses, ASE, etc). We used the Ti:Sa laser system (p-pol, 800 nm, 10 Hz, 40 mJ, 45 fs and 51018 W/cm2, ASE and prepulses 10����8 and less). Within some experiments the Nd:YAG laser (1064 or 532 nm, 30–120 mJ, 6 s, 1012 W/cm2) was used to create the controlled long and dense pre-plasma layer. This laser was locked with the Ti:Sa laser system with accuracy better than 1 ns. We performed optical (plasma emission, shadowgraphy and interferometry), X-ray and direct electron detection plasma diagnostics at different delays between the pulses and the focal positions of the main pulse. Different targets were used: metal plates made of Fe, Mo, W, thick polymer films and plates, liquid Ga, micro- and nanostructured materials. The brightest X-ray yield was achieved with 200–400 m thick plastic target. An X-ray spectrum slope was as high as 2.5 MeV at 1018 W/cm2 laser intensity (compare with the 200 keV slope without the nanosecond pre-pulse). For clarification of the electron acceleration mechanisms numerical simulations were done using fully relativistic 3D3V PIC code for laser-plasma interaction and electron acceleration. Parameters of nanosecond and femtosecond laser pulses coincided with the experimental ones.