Experimental and theoretical investigation of photoacoustic-signal generation by wavelength-modulated diode lasers

Wavelength modulation photoacoustic spectroscopy: Theoretical description and experimental results

“…More recently, we also developed an analytical expression of WMS harmonic signals in the particular case of a Lorentzian lineshape, but for the general situation of combined IM-FM with arbitrary phase shift [25]. PAS in combination with WM has already been discussed in the literature [10,[26][27][28][29][30], but mainly in the experimental point of view and explicit mathematical theory of WM-induced PAS (WM-PAS) has not been given. Even if this situation presents some similarities with standard WMS, there is however an important distinction due to the fundamental difference in the techniques, i.e.…”

Development and application of external-cavity diode laser systems for photoacoustic gas detection

“…One can already find considerable literature into this direction. Gases already measured with diode laser based photoacoustics include: water vapour [1][2][3] , ammonia [4] methane[5J , toluene[6 etc. However future spread of the method strongly depends on the availability of diode lasers suitable for gas detection applications .There are several factors to be considered simultaneously ranging over topics such as spectroscopic properties , reliability matters and also fmancial considerations.…”

Diode Laser Spectroscopic Monitoring of Trace Gases

“…(111,112,116) Hence, QEPAS can achieve a comparable sensitivity as conventional PAS, but with important benefits such as smaller size and reduced ambient acoustic noise impact. So far, QEPAS has been demonstrated with several simple molecules (106,117) using a single ro-vibrational line in fundamental MIR absorption bands (e.g. CO, N 2 O, H 2 CO, C 2 H 6 ) or in NIR combination bands (e.g.…”

“…In all cases, the presence of water vapor, even at low concentration, acts as a catalyst to hasten the molecular relaxation, which strongly enhances the PA response to the analyzed concentration. (117) Quartz-enhanced photoacoustic spectroscopy (QEPAS) introduced by Kosterev et al (106) is a variant of PAS, which maintains its main characteristics with the benefit of a quartz tuning fork (QTF) acting simultaneously as an acoustic sensor (instead of the traditional microphone) and as a miniature acoustic resonator (thus replacing the bulky PA cavity used in conventional PAS). This leads to an ultracompact, robust, and cost-effective trace-gas sensing module.…”

“…(116) While lower-power diode lasers such as NIR DFB lasers and MIR QCLs are now being used, (53,59,106,109,111,112,117) VCSELs are poorly suitable for PAS because of their much lower optical power. Surprisingly, the WM capabilities of diode lasers have found an elegant use in OAS -periodic tuning of the laser beam on and off the line resonance is also a good way to generate an acoustic wave.…”