Soft x-ray emission, angular distribution of hot electrons, and absorption studies of argon clusters in intense laser pulses

High resolution soft x-ray spectra (3-40 nm) produced by the interaction of intense femtosecond laser pulses with argon clusters at an intensity of about 1× 1016 W/ cm2 are measured under different backing pressures. Soft x-ray spectra are strongly dependent on the initial size of cluster and plasma expanding process. We find that laser polarization has no evident effect on the soft x-ray emission from the lateral side. The measurement on angular distribution of hot electrons shows that the resonant absorption is the dominated mechanism. Both the x-ray yield and the laser energy absorption are more efficient when the radius of cluster is comparable with the plasma resonant length.