Conceptual setup of the multi-frame interferometer.
Conceptual setup of the experiment. The carbon foil in the center of the image is simultaneously irradiated from both sides with the two heating laser beams. The interferometry beam probes the laser-generated carbon plasma while less than half of the probe beam crosses the plasma.
Interferograms of the target before (upper half) and 5.5 ns after the rise of the heating pulse (lower half). The fringes are shifted due to the phase shift induced by the free electron density. The target holder with a width of 1 mm is shown as the black vertical line. The experimentally not accessible region ends at a distance of 0.46 mm from the target surface.
Recorded phase shift at t = 12 ns to judge the influence of the assumption of cylindrical symmetry.
Evolution of the free electron density. The four images show the evaluated free electron density at 3.4 ns, 5.4 ns, 7.4 ns and 9.4 ns relative to 10% of the rising edge of the heating pulse. They cover the same spatial dimensions of 4 mm × 3 mm. The red crossed areas are experimentally not accessible due to the refraction of the probe beam. The scale of the free electron density is the same for all images and shown below the fourth image.
Evolution of the target normal free electron density profile for the experiment (solid line) and simulation (dotted line). The error for the free electron density is 0.5 × 1019 cm−3 and for the distance 50 μm.
Comparison of an interferometry image (lower half) and the corresponding results of the simulation (upper half), in which the red area represents the regions that are not imaged to the CCD camera while its corresponding free electron density is lower than the critical density of 8.8 × 1021 cm−3.
Deflection of the probe beam in function of the original normal distance from the target surface. The angle of acceptance is 0.72°, reached at a distance of 0.46 mm from the target surface.
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