Hollow microcylinder targets, 200–300 μm in diameter, have been internally irradiated at up to 5 · 1014 W/cm2 with Nd:glass laser pulses directed through an axial entrance slit. The plasma evolution in the interior of the cavities was diagnosed with a pinhole imaging X-ray streak camera and a Nomarski-type interferometer. Plasma collision near the center of the cylinder is observed about 300 ps after the irradiating laser pulse. The experimental results are confirmed by a one-dimensional Eulerian fluid code.

A novel type of ion spectrometer for laser-produced plasma diagnostics is described. The Thomson parabola configuration is used to separate the expanding plasma ions according to their different charge-to-mass ratios. One particular ion species is subsequently collected by a parabola-shaped charge collector. In this way ion velocity distributions of a single charge-to-mass ratio are obtained through simple time-of-flight analysis. Measured ion energies can be as low as 1 keV per nucleon.

Plasma was generated by focusing a 1.06-μm 35-psec laser pulse obliquely onto a solid surface at the optimum resonance absorption angle. The scaling of nonthermal ion emission energy with laser intensity was determined. A computer model for resonance absorption showed nonthermal ion emission to be due to electron acceleration by a resonantly driven electrostatic field.

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The absorption of laser radiation by inhomogeneous plasma is of considerable interest in laser fusion research. One process strongly affecting the absorption efficiency is density profile modification due to ponderomotive or radiation pressure at critical density, where most of the absorption occurs.

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