Allan variance for optimal signal averaging-monitoring by diode–laser and CO2 laser photo-acoustic spectroscopy

Abstract

The concept of the Allan variance has been utilized to test the detection abilities of two powerful experimental methods for trace gas monitoring: IR diode–laser and CO2 laser photo-acoustic spectroscopy. The detection of stable molecules (OCS, allene, CH3OH), and unstable species (ozone, short-lived free radical CN and molecular ion ArD+) have been compared. An approach for studies of the influence of the reactivity on the optimal averaging time for the minimum detectable concentration is demonstrated.