Abstract
Strong absorption increasing with intensity was observed in boron and gold laser plasmas heated by KrF laser pulses of high, but still nonrelativistic intensity. The pulses of 700 fs duration had a temporal contrast of 12 orders of magnitude, thus the laser pulse of >10^18 W/cm^2 intensity hit the steep surface of the boron and gold targets. Blue shift of the reflected radiation refers to extreme high acceleration resulting in velocities above 5*10^7 cm/s. Brunel absorption and ponderomotive effects are shown to play important role in the observed phenomena.
Highlights
Investigation of the light reflected from plasmas generated on solid surfaces is the most straightforward diagnostic of laser-plasma interactions, and the so-called plasma mirrors [1] are frequently used for improving the temporal contrast of intense subpicosecond laser pulses
increasing absorption was observed with increasing intensity
initially chirped laser pulse refers to a plasma propagation moving
Summary
Investigation of the light reflected from plasmas generated on solid surfaces is the most straightforward diagnostic of laser-plasma interactions, and the so-called plasma mirrors [1] are frequently used for improving the temporal contrast of intense subpicosecond laser pulses. The outward and inward motion of the plasma as derived from the reflectivity measurements resulted in the so-called block ignition idea which might become a way toward non-thermal ignition of ICF (inertial confinement fusion), reducing the requirements even for DT fusion or which might allow even the high temperature needed for p-B fusion [2, 3]. As based on earlier experiments [4, 5], the possible use of KrF lasers was emphasized [6]. For this reason we aimed to get more insight into KrF laser-plasma interactions under “clean” conditions where the temporal background before the main pulse does not modify the interactions. As an appropriate light source, the recently upgraded KrF laser system incorporating the newly installed Fourier-filtering technique [7] could be used, offering a short laser pulse with 1012 temporal contrast
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