Impact of atmospheric clutter on Doppler-limited gas sensors in the submillimeter/terahertz

Towards automated molecular detection through simulated generation of CMOS-based rotational spectroscopy

The use of CMOS sensors for rotational spectroscopy is a promising, but challenging avenue for low-cost gas sensing and molecular identification. A main challenge in this approach is that practical CMOS spectroscopy samples contain various different noise sources that reduce the effectiveness of matching techniques for molecular identification with rotational spectroscopy. To help solve this challenge, we develop a software application tool that can demonstrate the feasibility and reliability of detection with CMOS sensor samples. Specifically, the tool characterizes the types of noise in CMOS sample collection and synthesizes spectroscopy files based upon existing databases of rotational spectroscopy samples gathered from other sensors. We use the software to create a large database of plausible CMOS-generated sample files of gases. This dataset is used to help evaluate spectral matching algorithms used in gas sensing and molecular identification applications. We evaluate these traditional methods on the synthesized dataset and discuss how peak finding and spectral matching algorithms can be altered to accommodate the noise sources present in CMOS sample collection.

Terahertz Spectroscopic Molecular Sensor for Rapid and Highly Specific Quantitative Analytical Gas Sensing

Quantitative analytical gas sampling is of great importance in a range of environmental, safety, and scientific applications. In this article, we present the design, operation, and performance of a recently developed tabletop terahertz (THz) spectroscopic molecular sensor capable of rapid (minutes) and sensitive detection of polar gaseous analytes with near "absolute" specificity. A novel double-coil absorption cell design and an array of room-temperature sorbent-based preconcentration modules facilitate quantitative THz detection of light polar volatile compounds, which often challenge the capabilities of established gas sensing techniques. Acetone, ethanol, methanol, acetaldehyde, formaldehyde, and isoprene are detected at low parts-per-billion to high parts-per-trillion levels. This work evaluates performance-limiting factors for THz spectroscopy-based chemical identification: (1) spectral signal to noise and (2) preconcentrator efficiency.

Terahertz gas-phase spectroscopy: chemometrics for security and medical applications

We describe a spectrometer consisting of a vector network analyzer, a gas absorption cell, and a quasi-optical bench that acquires terahertz spectra of gaseous substances and mixtures. We tested volatile organic compounds that are medical biomarkers or chemicals which can be found on the US Environment Protection Agency list of harmful substances. Absorption spectra at gas pressures between 10 Pa and 5000 Pa were recorded. A subsequent multivariate data analysis demonstrated excellent qualitative and quantitative identification of pure substances and complex mixtures. The applied multivariate algorithms are principal components analysis, partial least square regression and soft independent modelling of class analogy.