An Algorithmic Approach to Compute the Effect of Non-Radiative Relaxation Processes in Photoacoustic Spectroscopy

Characterization of H2S QEPAS detection in methane-based gas leaks dispersed into environment

“…As CH 4 concentration increases above the per thousand scale, H 2 S QEPAS signal drops down reaching a plateau for concentrations > 4 %, corresponding to a peak value reduction of ∼ 70 %. Exponential decrease of PAS signal cannot be explained by simply assuming V-T relaxation but are clear evidence of the presence of V-V processes resulting in energy transfer to slower relaxation channels [42] , [57] , [58] . Based on the discussion presented in the first section, a V-V exchange from H 2 S* (ν 2 ) to CH 4 is likely to happen due to their similar energy.…”

“…In principle, a phase shift should be directly related to the above-mentioned V-T, V-V processes. [42] , [57] , [58] . Nevertheless, the relatively low operating pressure of 100 Torr used for all the measurements didn’t allow an unambiguous interpretation of the phase data.…”

A sub-ppbv-level Acetone and Ethanol Quantum Cascade Laser Based Photoacoustic Sensor – Characterization and Multi-Component Spectra Recording in Synthetic Breath

“…The photoacoustic signal generation is dependent on the photoacoustic relaxation efficiency (see Eq. (1) ), which can differ for every transition and depends on the bulk matrix composition [48] . This is caused by the different molecular relaxation pathways available.…”

“…To tackle the influence of changes in relaxation efficiency three different approaches exist. One is to characterize and compensate the gas matrix variations via measurements [37] , [49] , the other is a fully data driven approach, which applies machine learning to counter those effects building on a vast number of measurements [50] , and at last a purely analytical modeling backed up by precise measurements [48] . All those approaches have their unique advantages and disadvantages.…”

Detection of gaseous nerve agent simulants with broadband photoacoustic spectroscopy

“…Univocal calibration constant for different gas species necessitates constant non-radiative relaxation efficiency (here incorporated into A) between the considered species and possible gas mediums, which in general is not the case in PAS (Russo et al, 2021;Müller et al, 2022). However, the situation is considerably simplified here as our modulation frequencies around 300 Hz are unconventionally low for PAS and most importantly lower than the molecular relaxation rates in our gas matrices (Müller et al, 2022;Barreiro et al, 2012). Complete thermal relaxation enables the transfer of the calibration constant of CH 4 to simulant substances and nerve agents.…”