Comparison of Two Multipass Con gurations for Scattered Light Ampli cation

Scattered light ampli cation by using multipass method is a very useful technique to increase Thomson and Rayleigh scattering signals for local plasma electron temperature and density measurements. Using Rayleigh scattering in nitrogen neutral gas chamber, the well-known technique of multipass system with two concentrical spherical mirrors is compared with new con guration by using two sets of lens and at mirrors. The focusing capability of both con gurations makes the di erence to stray light and scattered signal related to spectrometer slit aperture and number of multipass. For the same number of laser beam pass and best slit aperture, the lens and plan mirrors new con guration presented lower stray light and higher scattered signal, although the gain of the usual two spherical mirrors still remains higher.