Experimental setup of the double PM system. An null telescope (spherical mirrors S1 and S2) creates an intermediate focus for the laser beam and then recollimates it; near this focus, the plasma mirrors (PM1 and PM2) are situated, both with a angle of incidence. The fluence on the PMs was varied by changing the radius of curvature of the deformable mirror (DM). Mirrors R1 and R2 on a kinematic slide permit the DPM to be inserted (solid line) or bypassed (dashed line). Final focus was created by an off-axis-parabolic mirror (OAP), and monitored by a CCD and a calorimeter.
Schematic of fluence measurement on PMs: -polarized beam reflects from PM1 and then PM2. The laser spots on both PMs were imaged onto web cameras (CAM1 and CAM2).
Spatial peak and overall reflectivity of the DPM system versus focal position. Spatial peak reflectivity: experimental result at the maximum reflectivity position (gray arrow), and numerical results over the whole range (solid circles). Overall reflectivity: experimental (open circles) and numerical results (crosses). The position of the focus is referenced with respect to the PMs: the zero of the axis corresponds to the focal spot positioned on the second PM. The random phase perturbation was different for each run of the simulation, producing the scatter observed in the numerical data sets.
Beam profiles on PM plates: (a) experimental observation and (b) numerical simulation of the fluence distribution on PM1; (c) experimental observation and (d) numerical simulation of the fluence distribution on PM2.
Focal spots in final target plane without and with the DPM system: (a) experimental observation and (b) numerical simulation of the final focus without the DPM system; (c) and (d) experimental and numerical results obtained for the final focus with the DPM system.
Normalized intensity distribution for three experimental shots with plasma mirror and three experimental shots without plasma mirror (left side of graph) and corresponding radial integrated energy (right side of graph) for the six shots. Dashed line: without DPM; solid line: with DPM. The addition of the DPM reduces the energy deposited outside the focal spot, as compared to the case without DPM.
Empirical spatial-peak fluence as a function of position around best focus: beam scan without (triangle and solid line, diamond and dashed line) and with (open circles, dotted) DPMs. For ease of comparison, all curves are normalized to unity. The lines are provided as a guide to the eye.
Front-edge steepening of the reflected pulse at different pulse energies. The original pulse shape (solid line) is compared to reflected pulses on the assumption of incident pulse energies of (dashed line), (dot-dashed line) and (dotted line).
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