Mid-infrared laser-based detection of benzene

Abstract

Benzene (C6H6) is one of the major public health concerns. It is emitted from various natural and anthropogenic sources, like fires and volcanic emissions, petrol service stations, transportation, and the plastics industry. Here, we present our work on developing a new benzene sensor using a widely tunable difference-frequency-generation (DFG) laser emitting between 11.56 and 15 µm (667-865 cm -1 ). The DFG process was realized between an external-cavity quantum-cascadelaser and a CO2 gas laser in a nonlinear, orientation-patterned GaAs crystal. We obtained the absorption cross-sections of the Q-branch of the ν4 vibrational band of benzene by tuning the wavelength of the DFG laser between 14.79 and 14.93 μm (670-676 cm -1 ). Benzene sensing measurements were performed near 14.84 µm (673.97 cm -1 ) with a direct laser absorption spectroscopy scheme. The benzene concentration was varied between ppb and ppm levels. Even with a relatively short optical path-length of 23 cm, our sensor achieved a benzene detection limit of about 10 ppb.

A laser-based sensor for selective detection of benzene, acetylene, and carbon dioxide in the fingerprint region

“…The selected wavelength range, however, has some spectral overlap between benzene, acetylene, and carbon dioxide. Although the band has been targeted previously for benzene detection [29,[32][33][34]43], spectral interference from CO 2 was not addressed, which can be signi cant at trace benzene concentrations. In this work, a multi-dimensional linear regression (MLR) algorithm, discussed in Section 2.2, is implemented to simultaneously measure benzene, acetylene, and CO 2 .…”

“…This limitation, combined with the aforementioned advantages of this spectral region, motivated researchers to use nonlinear conversion processes, such as difference-frequency generation (DFG) and optical parametric oscillation (OPO), to access such deep wavelengths in the IR region [26,27]. For instance, DFG has been used to probe benzene by accessing its 4 band (Herzberg's numbering) near 14.84 m [28,29] and HCN by accessing its 2 band near 14 m [30]. However, such non-linear conversion techniques are complicated and involve bulky setups, which de es some of the main bene ts of laser-based sensors.…”

Enhancement of photoacoustic spectroscopy with sorption enrichment for ppt-level benzene detection

“…These are common interferents in benzene measurements and the requirement to properly account for their presence can degrade the performance of the detector substantially [16]. Another strong absorption band at 14.8 µm has also been used for ppb-level benzene detection [17,18], but previously a long preconcentration time of 40 min was required for single digit ppb measurements [17].…”