Sophie Eliet

Versatile Sub-THz Spectrometer for Trace Gas Analysis

A THz sensor system based on a commercially available multiplier chain is applied to the analysis of trace gases. Frequency modulation of the source is used to achieve the high sensitivity required. Particular attention is paid to the line broadening effect caused by the modulation as this can hamper the quantification of the various chemical species being monitored. A numerical model using a Voigt absorption profile along with a single calibration step is used to provide quantitative information. The sensitivity obtained by this prototype instrument permits the analysis of various samples extracted during the industrial sintering of iron ore as part of the manufacturing of steel.

Continuous Monitoring of Formaldehyde Photolysis Products by THz Spectroscopy

A terahertz sensor system based on a commercially available multiplier chain operating in the range 600-900 GHz is used to monitor the photolysis of formaldehyde H2CO. The exposure of formaldehyde to solar radiation provokes dissociation via two pathways: 1) the molecular channel producing molecular carbon monoxide CO and 2) the radicalar channel giving formyl HCO. Monitoring the concentrations of CO and H2CO via pure rotational transitions, allowed us to obtain the kinetic rate constants for these two channels. In order to establish the detection limit of HCO, a modified spectrometer configuration employing the Zeeman modulation was used with acetaldehyde CH3CHO and photosensitization by mercury.