Methods of tunable diode laser absorption saturation spectroscopy to gas sensing under optically thick conditions

Abstract

The absorption saturation under optically thick conditions will bring difficulties to laser spectroscopy gas sensing. We report the spectrum two wings reconstruction method and the transmitted laser intensity fitting method for tunable diode laser absorption saturation spectroscopy gas absolute measurements under optically thick conditions, and used the modified Lambert Beer's law to calculate methane concentration based on the incomplete spectrum of absorption saturation. The maximum deviation between the experimental measurement results and the standard methane concentration is about 4.7%, which verifies the feasibility of these new methods and also show that they have great potential for expanding the gas sensing range of a single absorption line.

Estimation of Staphylococcus aureus growth rates from CO2 with absorption spectroscopy

“…In the past few years, the use of wavelength modulated absorption spectroscopy (WMAS) technology to monitor the growth of microorganisms has aroused considerable interest because of its characteristics including high sensitivity, high selectivity, high resolution, simple structure, and non‐invasiveness, which are indispensable to develop a fast online detection method 17–21 . Actually, it has been widely used in trace gas analysis, 22–24 chemical reaction process measurement, atmospheric environment monitoring, industrial combustion control, early disease diagnosis and screening, aeroengine stability test and many other application fields 25–28 .…”

A LabVIEW‐based TDLAS methane detection system using a wavelet denoising method

“…8,9 In this case, it is necessary to design a high-precision CH 4 detection system to detect methane concentration in real time. [10][11][12][13][14] Tunable diode laser absorption spectroscopy (TDLAS) is a detection method that tuning a tunable laser cover the target gas absorption line to realize the high selectivity and sensitivity detection. [15][16][17][18] However, most of the systems were tested in the laboratory environments, when they are employed in the industrial circumstances, the performances would decrease with various interrupts, such as power, temperature, humidity and vibrate fluctuation.…”

Theoretical analysis of wavelength modulation laser heterodyne spectroscopy

“…Even though wavelength modulation laser heterodyne radiometer has been well developed, the lack of theoretical analysis is a major limitation with the optimization of the laser heterodyne harmonic signal, which greatly depends on the intensity modulation and the modulation index. [20][21][22][23][24][25] However, so far, few theoretical analyses are discussed in the details, and therefore the theory of direct absorption spectrum is often utilized as an alternative theory to laser heterodyne spectroscopy. It should be noted that according to the basic concept of the spectroscopy, there is a great difference between direct absorption spectroscopy and laser heterodyne spectroscopy.…”