2021
Abstract
Abstract
Abstract
Abstract
Compact, rugged and sensitive laser-based trace gas sensors are in high demand for science and commercial applications. To ensure high sensitivities, laser spectroscopic sensors often use extended interaction paths (e.g. multi-pass cells), which significantly increases their size, weight and susceptibility to misalignment. Herein, we present a novel, miniaturized photothermal gas sensor, where the gas sample is measured inside the resonator of a monolithic microchip solid-state laser operating at 1064 nm. The photothermal-induced gas refractive index variations are directly translated to a solid-state laser frequency shift, which is detected as a beatnote modulation in a heterodyne detection scheme. The system provides high sensitivity to refractive index changes at the level of ∼1.1 × 10−12 within ultra-short intra-cavity interaction path-length of 1.5 mm, which enables trace-gas measurements in a sensing volume of only 4 μl. In a proof-of-concept experiment using dry carbon dioxide as a test sample the sensor reached a minimum detection limit of 350 ppbv for a 100 s averaging time and NNEA = 4.1 × 10−8 [W cm−1 Hz−1/2].
2020
Abstract
Abstract
Abstract
Abstract
Abstract
Understanding the multi-channel dynamics of O(1D) reactions with unsaturated hydrocarbon molecules in low temperature reaction kinetics is critically important in stratospheric chemistry, plasma chemistry, plasma assisted fuel reforming, materials synthesis, and plasma assisted combustion. A photolysis flow reactor coupled with highly selective mid-infrared Faraday Rotation Spectroscopy (FRS) and direct ultraviolet-infrared (UV-IR) absorption spectroscopy (DAS) techniques was developed for the first time to study the multi-channel dynamics of excited singlet oxygen atom O(1D) reactions with C2H2 and the kinetics of subsequent reactions. Time-resolved species concentrations of OH, HO2 and H2O were obtained and used to develop a validated kinetic model of O(1D) reactions with C2H2. The branching ratios of O(1D) reaction with C2H2 and subsequent HO2 kinetics were also quantified. It is found that, contrary to O(1D) reactions with saturated alkanes, OH formation via direct H abstraction by O(1D) is negligible. The results revealed that two chain-branching and propagation reactions via direct O(1D) insertion are the major pathways for radical production. The present study clearly demonstrated the advantage of radical detection and kinetic studies using FRS in the effective suppression of absorption interference from non-paramagnetic hydrocarbons.