TIME-RESOLVED, SIMULTANEOUS DENSITY, TEMPERATURE, AND ABSORPTION-MEASUREMENTS IN DENSE LASER-PRODUCED PLASMAS

We describe an optical diagnostic setup which permits simultaneous spatially and temporally resolved measurements of temperature and density from cold, dense laser-produced plasmas. Such information is necessary to investigate the physics of strongly coupled plasmas. The plasma is created in a slab geometry such that the transverse slab dimension is approximately one optical depth of the probing radiation in thickness. To perform the measurements the 2nd harmonic (λ=0.527 μm) of a mode-locked Nd:glass laser (τpulse=300-500 ps) is split into two orthogonally polarized beams. One of the beams measures plasma electron density using polarization wave front interferometry. The other beam uses a set of fast (τ=350 ps) photodiodes to measure single-frequency optical absorption. Plasma electron temperature is determined from time-resolved absolute emission measurements combined with the optical absorption measurements via Kirchoff's law. This technique avoids the difficulties involved in spectroscopic temperature measurements, where the spectral intensities and line profiles are affected by the physics of the cold, dense plasma. A set of timing fiducials allows the entire set of diagnostics to be synchronized in time, while an accurate, self-referenced alignment system assures that all diagnostics sample the same region of plasma volume.