Continuous monitoring of nitric oxide at 5.33 μm with an EC-QCL based Faraday rotation spectrometer: laboratory and field system performance

Abstract

Abstract (100 words): Nitric oxide detection with Faraday rotation spectroscopy offers excellent sensitivity and high specificity together with outstan ding long term system performance. Development of a transportable, cryogen-free, prototype field instrument based on mode-hop-free external cavity quantum cascade laser targeting the optimu m NO Q(3/2) transition at 1875.8 cm -1 is reported . The system shows a minimum detection limit of 5.4 ppb with a 1sec. lock-in time constant. Continuous, unattended NO monitoring with >1 hour white noise limited averag ing times is reported. Keywords : nitric oxide, quantum cascade laser; laser spectroscopy, Faraday effect, trace-gas detection, 1. INTRODUCTION Detection of nitric oxide (NO) is of importance in a number of applications including environmental pollution monitoring, or medical diagnostics (e.g. in exhaled breath by asthma patients). By targeting fundamental ro-vibrational transitions of NO at 5.3—m sensitive concentration measurements can be performed using spectroscopic methods [1, 2]. Faraday rotation spectroscopy (FRS) is an extremely sensitive technique for the detection of paramagnetic species [3-5]. Under influence of a magnetic field the NO transitions undergo Zeeman splitting, which causes a rotation of the polarization of linearly polarized light interacting with the molecules. The best sensitivity for FRS NO detection can be obtained using the Q(3/2) transition at 1875.8cm