A multiple-pass cell for mid-IR spectrometry that has been designed to oper
ate in an evacuable environmental chamber is described. Using this new modi
fied White arrangement, we can significantly increase the path length while
keeping the spectrometric beam stable. An approximate expression that ties
the number of reflections to the optimal signal-to-noise ratio in multiple
-reflection cells is derived. (C) 1999 Optical Society of America.