Abstract
Gas sensing plays a key role in the progress towards a healthier, safer
and more sustainable society. The amount of gas sensing applications are
immense with varying requirements, and thus numerous sensors with
different characteristics are needed. This thesis contributes to the
task by introducing a new optical gas sensing technique, Fourier
transform photoacoustic spectroscopy (FT-PAS) implemented with a
spectrally broadband mid-infrared laser and a sensitive cantilever
microphone. The main benefits of FT-PAS are the fast acquisition of a
wide spectral range that is only limited by the light source, and the
effective enhancement of sensitivity with a high-power light source. Two
light sources are demonstrated in this thesis, namely an incoherent
fiber-based supercontinuum and a frequency down-converted mode-locked
optical frequency comb. Besides high power spectral density, the
advantage of broadband lasers stems from their high spatial coherence
enabling high spectral resolution and efficient coupling to multipass
cells.
The performance of cantilever-enhanced FT-PAS is excellent while requiring a sample volume of less than ten milliliters. The detection limit for methane is 90 parts per billion in five seconds, which can be significantly lowered through longer averaging. The highest demonstrated spectral resolution is 0.013 cm−1 with no compromise in the detection sensitivity and limited by pressure broadening. However, two orders of magnitude worse spectral resolution already provides sufficient selectivity for complex multi-species detection. The unique combination of high performance and low gas consumption makes the technique attractive for the analysis of volatile substances and samples with limited availability. The detection of chemical warfare agents for forensic crime scene investigation and online warning systems is one potential application of the technique demonstrated in this thesis. In the near future, both the performance and the applicability of FT-PAS are expected to remarkably improve, establishing the technique as a notable alternative in many industrial, medical and security applications.
The performance of cantilever-enhanced FT-PAS is excellent while requiring a sample volume of less than ten milliliters. The detection limit for methane is 90 parts per billion in five seconds, which can be significantly lowered through longer averaging. The highest demonstrated spectral resolution is 0.013 cm−1 with no compromise in the detection sensitivity and limited by pressure broadening. However, two orders of magnitude worse spectral resolution already provides sufficient selectivity for complex multi-species detection. The unique combination of high performance and low gas consumption makes the technique attractive for the analysis of volatile substances and samples with limited availability. The detection of chemical warfare agents for forensic crime scene investigation and online warning systems is one potential application of the technique demonstrated in this thesis. In the near future, both the performance and the applicability of FT-PAS are expected to remarkably improve, establishing the technique as a notable alternative in many industrial, medical and security applications.
| Original language | English |
|---|---|
| Place of Publication | Tampere |
| Publisher | Tampere University |
| ISBN (Electronic) | 978-952-03-2845-0 |
| ISBN (Print) | 978-952-03-2844-3 |
| Publication status | Published - 2023 |
| Publication type | G5 Doctoral dissertation (articles) |
Publication series
| Name | Tampere University Dissertations - Tampereen yliopiston väitöskirjat |
|---|---|
| Volume | 777 |
| ISSN (Print) | 2489-9860 |
| ISSN (Electronic) | 2490-0028 |
