TY  - JOUR
AU  - Lu, W.
AU  - Nicoul, M.
AU  - Shymanovich, U.
AU  - Tarasevitch, A.
AU  - Zhou, P.
AU  - Sokolowski-Tinten, K.
AU  - von der Linde, D.
AU  - Masek, M.
AU  - Gibbon, P.
AU  - Teubner, U.
TI  - Optimized K alpha x-ray flashes from femtosecond-laser-irradiated foils
JO  - Physical review / E
VL  - 80
IS  - 2
SN  - 1539-3755
CY  - College Park, Md.
PB  - APS
M1  - PreJuSER-5853
SP  - 026404
PY  - 2009
N1  - This work was supported by the Deutsche Forschungsgemeinschaft (Contract No. SFB 616 and Grants No. GI 300/3-1, No. TE 190/6-1, and No. So 408/6-3) and the European Union (Marie-Curie-network FLASH).
AB  - We investigate the generation of ultrashort K alpha pulses from plasmas produced by intense femtosecond p-polarized laser pulses on Copper and Titanium targets. Particular attention is given to the interplay between the angle of incidence of the laser beam on the target and a controlled prepulse. It is observed experimentally that the K alpha yield can be optimized for correspondingly different prepulse and plasma scale-length conditions. For steep electron-density gradients, maximum yields can be achieved at larger angles. For somewhat expanded plasmas expected in the case of laser pulses with a relatively poor contrast, the K alpha yield can be enhanced by using a near-normal-incidence geometry. For a certain scale-length range (between 0.1 and 1 times a laser wavelength) the optimized yield is scale-length independent. Physically this situation arises because of the strong dependence of collisionless absorption mechanisms-in particular resonance absorption-on the angle of incidence and the plasma scale length, giving scope to optimize absorption and hence the K alpha yield. This qualitative description is supported by calculations based on the classical resonance absorption mechanism and by particle-in-cell simulations. Finally, the latter simulations also show that even for initially steep gradients, a rapid profile expansion occurs at oblique angles in which ions are pulled back toward the laser by hot electrons circulating at the front of the target. The corresponding enhancement in K alpha yield under these conditions seen in the present experiment represents strong evidence for this suprathermal shelf formation effect.
KW  - J (WoSType)
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000269637900082
DO  - DOI:10.1103/PhysRevE.80.026404
UR  - https://juser.fz-juelich.de/record/5853
ER  -