Standoff detection of gases using infrared laser spectroscopy

Abstract

ABSTRACT In this work we present a laser-based system for standoff/r emote, sensitive detection of gases based on a tunable diode laser source and Wavelength Modulation Spectroscopy method (WMS). System performance was experimentally characterized. The constructed device has pr oven its capacity of efficient detection of methane in ai r at the single ppm levels and distances from 10 to 50 m (distance to a scattering object). The minimum detection limit of the system was estimated at the level of 10 ppm-m for the standoff arrangement and the measurement path of approximately 20 m (round trip). Potential application of the device to hydrogen sulfide detection and current limitations in this area are discussed. Keywords: infrared spectroscopy, gas sensing, standoff detection, wavelength modulation spectroscopy, methane, hydrogen sulfide 1. INTRODUCTION Laser-based spectroscopy systems that use compact, tunable semiconductor laser sources (e.g. distributed feedback diode lasers, interband cascade lasers or quantum cascade lasers) are highly efficient and sensitive tools for gas detection, providing great robustness and flexibility [1-12]. These kind of systems have been intensively investigated especially over the last decade and can be realized in various stationary configurations using different spectroscopy methods. However, ability to effectively detect gases using a st andoff or remote approach (w ith scattering or reflective optical targets) is often desirable from the practical point of view [13-18]. Remote detection of hazardous gases such as methane (CH