Application of FM spectroscopy in atmospheric trace gas monitoring: a study of some factors influencing the instrument design

摘要

Abstract: Absorption spectroscopy with tunable diode lasers(TDLAS) is increasingly being used to monitoratmospheric trace gases down to high pptv-levels. Thesesensitivities have been achieved with low frequencywavelength modulation (WM). A sensitivity improvementby about two orders of magnitude was demonstrated witha high frequency modulation (FM) technique inexperiments with single pass absorption cells. Inpractical TDLAS instruments however, the achievablesensitivity improvement is limited by several factors.In this paper, limitations due to the use of multipassabsorption cells and due to the stability of theinstrument are discussed.!