Abstract
Multi-pass Thomson scattering is an attractive method for measuring electron temperature and density in low density plasmas. The feasibility of multi-pass laser optics consisting of two confocal spherical mirrors has been studied, and analytic expressions for the path have been obtained. These can be used to optimize the design under the given conditions. The effects of aberration, as well as positioning and alignment errors, were found to be critical for obtaining large transit numbers. Beam expansion resulting from aberration, surface roughness of the mirrors and diffraction is considered. Under practical conditions, transit numbers of about 37 (i.e., 19 round trips) are possible.
