rf electric field in the ion cyclotron frequency range (10 kHz-1MHz) is measured directly in the plasma using an emissive probe operated in a novel manner.
The dynamics of the laser-produced plasma in a gas filled chamber and in a gas jet were investigated using a relatively low intensity laser (I⩽5×1012 W/cm2) with long pulse duration (7 ns). Visualization methods such as the Mach–Zehnder interferometry and the shadow imaging were employed to characterize the shock velocity, electron densities, and temperatures in the laser-produced plasma. The electron density depletion on the laser propagation axis was observed in a gas jet but not in the gas filled chamber. Qualitative analysis for the density depletion is discussed by employing a fluid theory for the ambipolar diffusion of the plasma species. In the gas filled chamber, increase of the laser energy, and applied gas pressure results in faster and further propagation of the shock front with the distance-time relation of Rs∝t2/5, implicating an instantaneous energy release at a point. However, the plasma produced in a gas jet shows a rather linear relation of Rs∝t at early time (t⩽10 ns).
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