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We describe a soft-x-ray laser interferometry technique that allows two-dimensional diagnosis of plasma electron density with picosecond time resolution. It consists of the combination of a robust high-throughput amplitude-division interferometer and a 14.7-nm transient-inversion soft-x-ray laser that produces ~5-ps pulses. Because of its picosecond resolution and short-wavelength scalability, this technique has the potential for extending the high inherent precision of soft-x-ray laser interferometry to the study of very dense plasmas of significant fundamental and practical interest, such as those investigated for inertial confinement fusion. Results of its use in the diagnostics of dense large-scale laser-created plasmas are presented. OCIS codes: 350.5400, 140.7240, 120.3180, 340.7450.

Laser-driven shock compression of samples precompressed to 1 GPa produces high-pressure-temperature conditions inducing two significant changes in the optical properties of water: the onset of opacity followed by enhanced reflectivity in the initially transparent water. The onset of reflectivity at infrared wavelengths can be interpreted as a semiconductor↔electronic conductor transition in water, and is found at pressures above ∼130 GPa for single-shocked samples precompressed to 1 GPa. Our results indicate that conductivity in the deep interior of “icy” giant planets is greater than realized previously because of an additional contribution from electrons. [ABSTRACT FROM AUTHOR]

Soft X-ray laser interferograms were acquired to map the evolution of a dense plasma jet created by the laser irradiation of a solid copper triangular target. The plasma is observed to rapidly expand along the symmetry plane of the target, forming a narrow plasma plume with measured electron densities of up to 1.2 x [10.sup.20] [cm.sup.-3]. Index Terms--Plasma diagnostics, plasma jets, soft X-ray laser, soft X-ray laser interferometry.

A tabletop capillary discharge soft X-ray laser was used to acquire high-contrast interferograms that map the evolution of dense aluminum plasmas created by the laser irradiation of a 500-[micro]m-diameter semicylindrical cavity with 120-ps optical laser pulses of ~1.1 x [10.sup.12] - W x [cm.sup.-2] peak intensity. The measured electron density maps, which were compared with simulations, show that the plasma converges on axis where it collides to form a localized region with density exceeding 1 x [10.sup.20] [cm.sup.-3]. Index Terms--Colliding plasmas, plasma diagnostics, soft X-ray laser, soft X-ray laser interferometry.

A spatially planar (Δtime/time∼0.2%) longitudinal stress drive extending over millimeter scale lengths is used to shocklessly compress an aluminum sample to a peak stress of 210 GPa over nanosecond time scales. Direct laser irradiation onto the inner wall of an Au halfraum creates an x ray distribution with a near-uniform blackbody temperature of up to 137 eV. The x rays ablate material from a low-Z foil in a region of planarity closely matched to the diameter of the halfraum. The resultant ablatively driven shock is converted into a ramp-stress-wave in a secondary aluminum target through unloading across an intermediate vacuum gap. Higher peak stresses and shorter associated risetimes result from increasing input laser energy. Ramp-compression experiments can provide single shot equation-of-state data close to the isentrope, information on the kinetics of phase transformations, and material strength at high pressures. [ABSTRACT FROM AUTHOR]

A correction to the article "Laser-driven shock experiments on precompressed water: Implications for 'icy' giant planets" that was published in the 2006 issue is presented.

The physical mechanisms driving the collimation of dense plasma jets created by low-energy ( approximately 0.6 J) laser pulse irradiation of triangular grooves were studied for different target materials using soft-x-ray interferometry and hydrodynamic code simulations. The degree of collimation of jets created by irradiating C, Al, Cu, and Mo targets at intensities of I=1x10(12) W cm(-2) with 120 ps laser pulses was observed to increase significantly with the atomic number. Radiation cooling is found to be the cause of the increased collimation, while the main effect of the increase in mass is to slow the jet evolution.

The formation and evolution of a collisional aluminum plasma jet created by optical laser irradiation of triangular grooves with pulses of 120ps duration at an intensity of 1x10(12)W cm(-2) were studied with experiments and simulations. Series of high-contrast soft x-ray laser interferograms obtained with a 46.9nm laser mapped the plasma density evolution of an initially narrow plasma jet that expands along the symmetry plane and evolves into a broader plasma plume with significant side lobes. Two-dimensional simulations performed using the radiation hydrodynamic code HYDRA reveal that the jet formation is initiated by accelerated material ablated from the vertex and is augmented by the continual sequential arrival of wall material along the symmetry plane, where it collides and is redirected outward. Radiative cooling is identified as an important process in maintaining the collimation of the jet. These results demonstrate that well collimated collisional plasma jets with parameters in a range of interest can be generated with low-energy laser pulses (<1J) , opening the possibility of studying relevant plasma phenomena in a small laboratory setting.

The evolution of dense aluminum and carbon plasmas produced by laser irradiation of 500-microm -diam semicylindrical targets was studied using soft x-ray laser interferometry. Plasmas created heating the cavity walls with 120-ps -duration optical laser pulses of approximately 1x10;{12}Wcm;{-2} peak intensity were observed to expand and converge on axis to form a localized high-density plasma region. Electron density maps were measured using a 46.9-nm -wavelength tabletop capillary discharge soft x-ray laser probe in combination with an amplitude division interferometer based on diffraction gratings. The measurements show that the plasma density on axis exceeds 1x10;{20}cm;{-3} . The electron density profiles are compared with simulations conducted using the hydrodynamic code HYDRA, which show that the abrupt density increase near the axis is dominantly caused by the convergence of plasma generated at the bottom of the groove during laser irradiation.