Mid-Infrared Integrating Cavity Ring-Down Spectroscopy

Currently, there exists an unmet need for man-portable vapor phase detection systems for chemical warfare agents and toxic industrial compounds to be used by warfighters. Existing technologies are either too large or are portable, but do not possess the specificity and dynamic range required. Cavity ring-down spectroscopy (CRDS) is a promising approach, but commercially available units do not meet the warfighter requirements. To address this need and the challenges of regular CRDS, we propose to develop a modified CRDS approach: Mid-InfraRed Integrating Cavity Ring-Down Spectroscopy (MIR-ICRDS). In general, the main component of cavity ring-down spectroscopy system is an optical cavity that utilizes multiple reflections to allow probe light to interact multiple times with a gas volume, thereby improving the samples effective interaction length. While there has been significant progress on multipass optical cavities using specular reflection approaches, they require precise alignment that limits their usefulness in field environments. To overcome this trade off and provide an optical cavity that is fieldable, we will use diffuse reflectance in an integrating cavity to produce long pathlengths and alignment free operation. Integrating cavity ring-down spectroscopy (ICRDS) was first demonstrated in 2015 by Cone and colleagues in the UV and visible using a cavity made from fumed silica. These authors demonstrated reflectivities of 0.999 in the UV/VIS spectral range and the capability to detect low concentrations of chemicals in the gas and liquid phase. We propose to extent the concept of ICRDS to the infrared region and demonstrate a mid-infrared Integrating Cavity Ring-down Spectroscopy (MIR-ICRDS) system with robust analysis software making use of machine learning algorithms.