An open-path, hand-held laser system for the detection of methane gas

Abstract

We have developed an open-path hand-held gas detector incorporating a distributed feedback InGaAs laser diode at 1.65µm. Incorporated into a handheld transceiver unit, the emitted laser beam is backscattered from nearby surfaces, collected and focussed onto an amplified InGaAs detector using a 150mm diameter plastic Fresnel lens. At ranges of 4-5metres, a typical backscattered signal is 10's of nanowatts of laser light. Applying 2nd derivative wavelength modulation spectroscopy gives a sensitivity to methane of better than 10ppm over a one metre path length. A number of demonstration units have been fabricated and successfully evaluated by end users.

Standoff Chemical Detection Using Laser Absorption Spectroscopy: A Review

“…The commonly used optical structure for backscatter-TDLAS can be generally divided into two categories. The first approach uses a large-diameter Fresnel lens [110][111][112], as shown in Figure 4a. The simple structure is conducive to integrate a compact, lightweight and low-cost handheld system for short path standoff detection.…”

Mid-Infrared Tunable Laser-Based Broadband Fingerprint Absorption Spectroscopy for Trace Gas Sensing: A Review

“…In order to realize standoff gas detection, a number of laser-based techniques are available, such as TDLAS [34,35,137,138], PAS [139], differential absorption lidar (DIAL) [140], CLaDS [141], and more recently active coherent laser spectrometers (ACLaS) [36]. The basic architectures of these techniques are shown in Figure 2.…”

Recent Developments in Modulation Spectroscopy for Methane Detection Based on Tunable Diode Laser

“…Based on FMS, TDLs offer remote detection of methane gas the opportunity to operate over distances of 10 m or more in high sensitivity [111]. In these systems, the laser beam aimed through the probed region is collected after one-way transmission or further reflection from a topographic target [112,113].…”