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15DYNAMICS OF PLASMA EXPANSION IN INTENSE FEMTOSECOND LASER-ABLATED ALUMINUM PLUMES
A. Korytin, Yu. Mal'kov, A. Murzanev, A. Stepanov, D. Yashunin
Institute of Applied Physics RAS, Nizhny Novgorod, Russia
The results of investigating dynamics and parameters of plasma generated by intense femtosecond laser radiation (W < 150 mJ, t ~ 70 fs, I ~ 21017 W/cm2, nanosecond contrast ~ (2-5)-10-7) from metal Al foil are presented. Spatial distribution of plasma density at different time delays relative to the main powerful pulse creating plasma was measured by interferometry of a femtosecond probe pulse. The electron temperature was estimated from the bremsstrahlung X-ray spectrum measured by an X-ray CCD camera (Andor DO434). A typical interferometric image is presented in Fig. 1. The presence of a nanosecond prepulse leads to formation of extended plasma plume with characteristic scale of order 100 mkm before the arrival of the main pulse. The main powerful pulse interacts with the foil, ionizes it, and hot plasma propagates through the preplasma, forming a shock wave-like structure clearly seen in Fig. 1. Plasma density distribution of along the laser beam axis is presented in Fig. 2. The velocity of plasma expansion was approximately V ~ 1.5 107 cm/s and stayed constant over the observation periods (3.5 ns). The electron temperature in the plasma estimated from the X-ray spectrum was Te=2-2.5 KeV and corresponded to the observed velocity of plasma expansion.
Fig. 1. Interferometric image for time delay r=1.35 ns, lineposition of the foil_
Fig.2. Plasma density dependence on the distance from the foil
The results obtained on the generation of high density and high-speed plasma fluxes may be useful for modeling numerous astrophysical phenomena in laboratory.
