Resonant diagnostics of laser-produced Ba plasmas

Resonant laser probing diagnostics are used to observe laser-produced barium plasmas (n≤1015 cm−3, T≂1 eV) streaming (v≂106 cm/s) across a strong transverse magnetic field (10 kG). The interaction of the plasma with the magnetic field produces structure in the plasma. The observation of this structure requires resonant diagnostics because of the very low plasma density in this experiment. A YAG-pumped dye laser is tuned near the Ba ii 4554-Å transition for resonant absorption, shadowgraphy, and scattering measurements. Resonant absorption and shadowgraphy images reveal that the plasma expands across the field with virtually no inhibition from the field, while narrowing in the plane perpendicular to the field. In the plane of the magnetic field the expansion is highly structured, taking the form of very narrow jets aligned along the field lines. This structure appears to be a manifestation of a beam-plasma-type instability. For a comparison with theoretical predictions the plasma density and scale lengths are measured by resonant scattering.