A triple spectrograph system for low stray light Thomson scattering measurements

Thomson scattering is scattering of photons by the electrons in a plasma. From the scattering spectrum, the electron temperature and density (Te, ne) of the plasma can be deduced. In the past decade, the development of high power lasers and sensitive detection devices has made Thomson scattering a powerful diagnostic tool for small laboratory plasmas. However, measurements on plasmas close to a plasma applicator or contained in glass (e.g. gas discharge lamps) suffer from an excessive amount of stray light [1]. For plasmas with a low electron density and temperature, this is a serious problem; in fact, stray light often determines the detection limit. This paper discusses the design of a dedicated triple spectrograph detection branch to reduce the disturbing effect of stray light on Thomson scattering spectra