Several optical designs for GC/FT-IR have been investigated. It was found that reflection losses occurring in the light-pipe cause the solid angle of the emerging beam to be much smaller than that of the input beam. This property permits a very small image at the detector to be achieved since the collection mirror may be mounted well away from the end of the light-pipe. With an optical configuration of this sort, the effect of radiation emitted from the light-pipe saturating the response of the detector is also minimized.
