Аннотация: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.