Recovery of Absolute Gas Absorption Line Shapes Using Tunable Diode Laser Spectroscopy With Wavelength Modulation—Part 2: Experimental Investigation

In situ H2O and temperature detection close to burning biomass pellets using calibration-free wavelength modulation spectroscopy

“…Recently, several approaches for calibration-free WMS (CF-WMS) have been suggested [19][20][21][22][23][24][25], usually based on normalizing nf-WMS with 1f-WMS signals to account for instrumentation factors and a wavelength dependent laser intensity. CF-WMS systems were successfully employed for temperature and concentration measurements in shock-tubes [26], engines [27], scram-jet combustors in the presence of inhomogeneously distributed temperature and species concentration [28], and in coal-fired high pressure combustion facilities [29].…”

Chemical species tomography

“…This can be accomplished using additional wavelengths having a different balance of these two components, ideally including regions of negligible absorption. Depending on the absorption feature under consideration, this may be implemented by chirping a single source, in the manner typical of TDLAS measurements (Bain et al, 2011), or it may require multiple sources, as in the DWR approach used in Wright et al (2010). It is, however, apparent from example path P III,A that this approach does nothing to restrict the spatial origin of the measured absorption signal, with the relative weighting of the various paths within the envelope being determined by the source properties and the subsequent scattering and absorption processes.…”

Rapid detection of methane, carbon dioxide and ammonia for harsh environments using tunable doide laser spectroscopy

“…Both these methods were initially limited to low m-values that were well below the optimum value of m = 2 for 1f WMS. Recently, however, a way to overcome this problem using Fourier analysis of the Lortenzian line shape has been demonstrated [21,22], which makes these approaches attractive for industrial applications where one would aim to operate at high m-values to maximize the received signal strength.…”

“…The time resolution of 10s is limited by the current hardware and can be further increased by using a dedicated processor and a data acquisition system, instead of the oscilloscope and computer. The 1650nm laser diode used for methane detection has a relatively low phase-quadrature frequency of 99kHz as compared to one used by [22][23][24][25]. This fortuitous situation has enabled the use of RAM method at the phase-quadrature frequency to recover the absorption lineshape and to thereby achieve calibration-free measurement of the concentration of methane.…”