Electron Density Measurements of High Density Plasmas Using Soft X-Ray Laser Interferometry

Abstract

We have developed and used for the first time a soft x-ray interferometer to probe a large laserproduced plasma with micron spatial resolutions.A neonlike yttrium x-ray laser operating at 155 A was combined with a multilayer coated Mach-Zehnder interferometer to obtain electron density profiles in a plasma produced by laser irradiation of a CH target. The measured electron density profile has been compared to hydrodynamic simulations and shows good agreement near the ablation surface but some discrepancy exists at lower densities.

Picosecond X-Ray Laser Interferometry of Dense Plasmas

“…The density sampled by the x-ray laser occurs over a time interval dictated by the few picosecond duration of the x-ray laser pulse and its transit time through the 0.5 cm plasma column ( 16:5 ps). The electron density, n e in cm ÿ3 , is related to the measured fringe shifts as N fringe 6:68 10 ÿ20 n e L, where L is the length (cm) of the plasma being probed by the 14.7 nm x-ray laser [4]. Fringes are clearly visible less than 10 m from the target surface.…”

“…For example, Attwood et al successfully employed a 15 ps duration, 266 nm wavelength probe to determine density profile steepening close to the target surface [1]. Also, short wavelength, , high brightness probe beams allow for characterization of large plasmas at high density with less deleterious effects from free-free absorption f/ 3 1ÿ exp ÿhc= kT g and refraction (/ 2 ) [4]. Da Silva et al first demonstrated the technique in the extreme ultraviolet with the NOVA generated a 15.5 nm Ne-like Y collisional x-ray laser, using a Mach-Zehnder interferometer with thin multilayer beam splitters [4].…”

“…Also, short wavelength, , high brightness probe beams allow for characterization of large plasmas at high density with less deleterious effects from free-free absorption f/ 3 1ÿ exp ÿhc= kT g and refraction (/ 2 ) [4]. Da Silva et al first demonstrated the technique in the extreme ultraviolet with the NOVA generated a 15.5 nm Ne-like Y collisional x-ray laser, using a Mach-Zehnder interferometer with thin multilayer beam splitters [4]. The high brightness of the 350 ps probe enabled electron densities of 10 21 cm ÿ3 to be diagnosed in a large millimeter-scale CH plasma.…”

Extremely compact soft X-ray lasers based on capillary discharges

“…The elongated gold-coated mirrors redirect the beam towards the second grating where they are recombined and the interference pattern is generated. Advantages of the DGI scheme over other amplitude-division soft X-ray interferometers based on thin-film beam splitters [10,14] include a higher throughput (B6% percent per arm) and a significantly increased resistance of the beam splitters to plasma debris. A Si/Sc multilayers optics system was used to image the plasma onto a CCD/MCP detector setup with 51.2 Â magnification.…”

“…Da Silva et al conducted the first soft X-ray laser interferometry experiments using a laboratory-size 15.5 nm Nelike Y laser pumped by the Nova laser in conjunction with a Mach-Zehnder interferometer based on thin-film beam splitters [10]. Capillary discharge-pumped soft X-ray lasers, with an extremely high brightness that is similar or higher than that of their laboratory-size predecessors and a much higher repetition rate, offer the opportunity to develop portable soft X-ray tools for the diagnostics of a large variety of dense plasmas.…”