Comparison of two multipass configurations for scattered light amplification

Scattered light amplification by using multipass method is a very useful te chnique to increase Thomson and Rayleigh scattering signals for local plasm a electron temperature and density measurements. Using Rayleigh scattering in nitrogen neutral gas chamber, the well-known technique of multipass syst em with two concentrical spherical mirrors is compared with new configurati on by using two sets of lens and flat mirrors. The focusing capability of b oth configurations makes the difference to stray light and scattered signal related to spectrometer slit aperture and number of multipass. For the sam e number of laser beam pass and best slit aperture, the lens and plan mirro rs new configuration presented lower stray light and higher scattered signa l, although the gain of the usual two spherical mirrors still remains highe r.