ИСТИНА

Plasma created by a relativistically intense femtosecond laser pulse can be used as a brilliant source of ultra-short bursts of high energy photons in X- ray and γ-ray diapasons. Besides of the laser pulse intensity, its duration and temporal structure (pre-pulses, leading edge sharpness, ASE level and duration) determine pre-plasma scale and length, that in its turn give rise to the different acceleration mechanisms. In this paper we present experimental results and numerical 3D PIC simulations on hard x-ray and gamma-emission from plasma created by the ultrashort relativistic laser pulse. We varied its intensity, duration and contrast to reveal key electron acceleration mechanisms and to optimize the photon yield for different applications. We used Ti:Sapphire laser system, which generates femtosecond pulses (40fs, 100mJ, 10Hz) of relativistic intensity (up to 1019W/cm2 ). Different laser pulse contrasts were used from 10−5 to better than 10−10. Pulse duration was changed by the grating compressor detuning. To create an artificial pre-pulse sliced ultrashort pulse, uncompressed pulse or long 13 ns pulse from the external active mode-locked Nd:YAG laser was used. The pre - pulse intensity of the target was also adjusted to control pre-plasma characteristics.