Photoacoustic-based detector for infrared laser spectroscopy

Abstract

In this contribution, we present an alternative detector technology for use in direct absorption spectroscopy setups. Instead of a semiconductor based detector, we use the photoacoustic effect to gauge the light intensity. To this end, the target gas species is hermetically sealed under excess pressure inside a miniature cell along with a MEMS microphone. Optical access to the cell is provided by a quartz window. The approach is particularly suitable for tunable diode laser spectroscopy in the mid-infrared range, where numerous molecules exhibit large absorption cross sections. Moreover, a frequency standard is integrated into the method since the number density and pressure inside the cell are constant. We demonstrate that the information extracted by our method is at least equivalent to that achieved using a semiconductor-based photon detector. As exemplary and highly relevant target gas, we have performed direct spectroscopy of methane at the R3-line of the 2v3 band at 6046.95 cm−1 using both detector technologies in parallel. The results may be transferred to other infrared-active transitions without loss of generality.

Towards Integrated Mid-Infrared Gas Sensors

“…Various strategies have been used to implement the acoustic detector, Table 2. These include designs based on gas-filled [15,44,50,51,69,80,85], or unfilled MEMS microphones [66,67,71,72], optical microphones based on Fabry–Pérot interferometers (FPIs) [68,82], or quartz tuning forks (QTFs) [83,84]. Table 2 summarizes representative operation performances.…”

Investigating flexible feeding effects on the biogas quality in full‐scale anaerobic digestion by high resolution, photoacoustic‐based NDIR sensing

“…Modulation of the light source leads to the exiting soundwave whose amplitude is related to the amount of target gas in the measurement channel. About a decade ago, the first attempt to miniaturize this simple concept did use a micro-electro-mechanical system pressure sensor to gauge the light intensity of a thermal emitter [22], and since then different combinations of various types of broad band light sources and devices for determining the photoacoustic signal have been developed [23][24][25][26][27][28][29][30][31]. While the use of lasers in combination with acoustic resonators in setups of direct photoacoustic spectroscopy allow for ultra-sensitive trace gas detection, the use of such devices outside the laboratory is challenging [32][33][34][35][36].…”

On-Board Monitoring of SO2 Ship Emissions Using Resonant Photoacoustic Gas Detection in the UV Range

“…Publications on photoacoustic gas sensors using a light-emitting diode (LED) as a light source and a microphone or a quartz tuning fork as an acoustic transducer can be found for CO 2 detection [ 10 , 11 ] and methane detection in [ 12 , 13 ]. Laser-based systems can be found, for example, in [ 14 ] where a microphone is used as a transducer to detect CH 4 . Another example is an ethylene measurement device presented in [ 15 ], which uses a cantilever as a transducer.…”