International Journal of Thermophysics

, Volume 34, Issue 8, pp 1661-1665

First online:

\(\text{ CO}_{2}\) Laser-Based Pulsed Photoacoustic Ammonia Detection

  • Arturo VallespiAffiliated withCEILAP-UNIDEF-CITEDEF, Juan Bautista de La Salle 4397 (B1603ALO) Email author 
  • , Verónica SlezakAffiliated withCEILAP-UNIDEF-CITEDEF, Juan Bautista de La Salle 4397 (B1603ALO)
  • , Alejandro PeuriotAffiliated withCEILAP-UNIDEF-CITEDEF, Juan Bautista de La Salle 4397 (B1603ALO)
  • , Guillermo SantiagoAffiliated withLaboratorio Láser, Facultad de Ingeniería, Universidad de Buenos Aires

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Detecting ammonia traces is relevant in health, manufacturing, and security areas, among others. As ammonia presents a strong absorption band (the \(\nu _{2}\) mode) around 10 \(\upmu \)m, some of the physical properties which may influence its detection by means of pulsed photoacoustic (PA) spectroscopy with a TEA \(\text{ CO}_{2}\) laser have been studied. The characteristics of the ammonia molecule and the laser intensity may result in a nonlinear dependence of the PA signal amplitude on the laser fluence. Ammonia absorption can be described as a simple two-level system with power broadening. As \(\text{ NH}_{3}\) is a polar molecule, it strongly undergoes adsorption phenomena in contact with different surfaces. Therefore, physical adsorption–desorption at the cell’s wall is studied. A theoretical model, based on Langmuir’s assumptions, fits well to the experimental results with stainless steel. Related to these studies, measurements led to the conclusion that, at the used fluenced values, dissociation by multiphotonic absorption at the 10P(32) laser line may be discarded. A calibration of the system was performed, and a detection limit around 190 ppb (at 224 \(\text{ mJ}\cdot \text{ cm}^{-2}\)) was achieved.


Adsorption Ammonia Photoacoustics