Electron density measurement via dual-angle Thomson scattering diagnosis

In this article, we present experiments measuring the electron density of a blown-off aluminum plasma created by a 2 ω (532 nm) laser using dual-angle Thomson scattering diagnosis. By fitting two ion-acoustic-wave feature spectra collected from two angles simultaneously, in a typical shot, the electron density obtained 400  μm in front of the target as given by Thomson scattering diagnosis was ( 5.9 ± 0.6 ) × 10 18 cm − 3, which is 35% higher than the average result of ( 4.4 ± 0.7 ) × 10 18 cm − 3 as measured by digital holography diagnosis. The distribution of the electron density along the laser axis from 400  μm to 700  μm as given by dual-angle Thomson scattering was broadly consistent with that obtained from digital holography diagnosis. At a location of 250  μm in front of the target, a unique set of plasma parameters cannot be obtained by dual-angle Thomson scattering diagnosis. This may be a result of the steep density gradient visible in the hologram in this region. Dual-angle Thomson scattering diagnosis can provide a good estimation of the electron density in plasma parameter regimes similar to those in these experiments, in which the scattering parameter α < 2. This technique may be useful for small laser facilities that cannot afford a second probe laser with a different wavelength and for measuring electron density with 4 ω Thomson scattering on large laser facilities. This article presents several factors that need to be considered when employing this method.