Spectroscopy

Quantum mechanics

Catalysis

Photoacoustic effect

Materials science

Quantum cascade laser

Absorption (acoustics)

Biochemistry

Carbon monoxide

Photoacoustic spectroscopy

Laser

Transducer

Physics

Nanotechnology

Organic chemistry

Optics

Terahertz radiation

Interferometry

Photothermal therapy

Photothermal spectroscopy

Resonator

Composite material

Time delay and integration

Chemistry

Photoacoustic imaging in biomedicine

Optoelectronics

Absorption spectroscopy

Parts-per notation

Photoacoustics

We report on a comparison between two optical detection techniques, one based on a Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) detection module, where a quartz tuning fork is acoustically coupled with a pair of millimeter-sized resonator tubes; and the other one based on a Photothermal Spectroscopy (PTS) module where a Fabry-Perot interferometer acts as transducer to probe refractive index variations. When resonant optical absorption of modulated light occurs in a gas sample, QEPAS directly detects acoustic waves while PTS probes refractive index variations caused by local heating. Compact QEPAS and PTS detection modules were realized and integrated in a gas sensor system for detection of carbon monoxide (CO), targeting the fundamental band at 4.6 μm by using a distributed-feedback quantum cascade laser. Performance was compared and ultimate detection limits up to ∼ 6 part-per-billion (ppb) and ∼15 ppb were reached for QEPAS and the PTS module, respectively, using 100 s integration time and 40 mW of laser power.

Parts-per-billion detection of carbon monoxide: A comparison between quartz-enhanced photoacoustic and photothermal spectroscopy