A Review of Signal Enhancement and Noise Reduction Techniques for Tunable Diode Laser Absorption Spectroscopy

Abstract

Tunable diode laser absorption spectroscopy (TDLAS), as a noninvasive spectroscopic method, permits high-resolution, high-sensitivity, fast, in situ absorption measurements of atomic and molecular species and narrow spectral features in gaseous, solid, and liquid phases. Advances in new diode laser sources and laser spectroscopic techniques generally have triggered an increasing application of TDLAS in various disciplines (for example, atmospheric environmental monitoring, chemical analysis, industrial process control, medical diagnostics and combustion monitoring, etc.) over the last four decades. This article reviews some important developments in TDLAS, from its basic principles as a spectroscopic tool to the demonstration of gas absorption measurements, emphasizing signal enhancement and noise reduction techniques developed for improving current TDLAS performance.

Opportunities for photonic integrated circuits in optical gas sensors

“…A small overview, not aiming for completeness, will be given here. A comprehensive study can be found in [39]. It is worth mentioning that PICs can incorporate all of the schemes mentioned here, with negligible impact on the footprint or cost of the devices.…”

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

“…However, optical interference fringe, the primary cause of background fluctuation, has not been effectively suppressed in WMS. Many methods, including the adoption of post-detection filtering and the improvement of the detection system, have been attempted to optimize the optical interference fringe in methane sensors [97]. For example, recently, a method of combining dual tone modulation (DTM) with vibration reflector (VR) was introduced, which decreased the standard deviation (STD) value of the background signal to 0.0924 ppm [98].…”

A TDLAS Sensor for Simultaneous Measurement of Temperature and C2H4 Concentration Using a Differential Absorption Scheme at High Temperature

“…Through an investigation of relevant literature, it has been found that there are many studies on measurements of species concentration and temperature by direct absorption spectroscopy (DAS) or wavelength modulation spectroscopy (WMS) employing isolated absorption lines of the measured gas molecules [12][13][14][15][16][17][18][19]. However, for the molecules with dense absorption spectral features (such as ethylene and methane, which contain hydrocarbon bonds), there will be self-mixing or overlap with other molecules at an elevated temperature and pressure, making it difficult to accurately infer the complete transition properties through a single line or line pair.…”