Quantum cascade laser-based trace detection of gases in the deepinfrared region using phase-fluctuation optical heterodyne spectroscopy

摘要

We present a spectroscopic technique based upon optical phase-fluctuation spectroscopy for very high levels ofsensitivity and specificity with application for detecting the presence of concealed explosives by detection in the vaporphase. The approach enables recent advances in deep-infrared QCL spectroscopic sources to be utilised without the needfor cooled detectors and gives multi-pass Herriott-type cell performance from a highly compact form factor. The systemhas been evaluated in the mid-infrared using a continuous-wave optical parametric oscillator as a spectroscopicexcitation source, and Ethane as a sample molecule for detection. With this setup we have demonstrated the specificity ofthe device by being able to resolve characteristic spectral lines of the molecule of interest against other contaminants inthe sample with similar spectral response, and a noise-equivalent sensitivity of 15ppb. Sensitivity is currently limited byambient mechanical noise and routes to minimize this are considered.