Electron density measurement by deflection of a far-infrared beam

Abstract

Electron densities in the range 3×1014<Ne<6×1015 cm−3 have been determined in a laser-initiated linear discharge using a novel far-infrared method. The density was determined by measuring deflections of a 119- and 171-μm far-infrared beam from an optically pumped CH3OH laser. The far-infrared beam was guided both inside and outside of the plasma chamber using dielectric waveguides. The spatial distribution of electron density for peak discharge currents of 2–4 kA and at distances of 8–25 mm from the laser focus on the target was found to be given by Ne (r,ϑ,I) =3×1014I1.9r−2.4 cosω cm−3, where I is the discharge current in kA, r is the radius from the laser focus on the target in cm, and ϑ is the polar angle from the target axis.