ICL-Based OF-CEAS: A Sensitive Tool for Analytical Chemistry

Abstract

Optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) using mid-infrared interband cascade lasers (ICLs) is a sensitive technique for trace gas sensing. The setup of a V-shaped optical cavity operating with a 3.29 μm cw ICL is detailed, and a quantitative characterization of the injection efficiency, locking stability, mode matching, and detection sensitivity is presented. The experimental data are supported by a model to show how optical feedback affects the laser frequency as it is scanned across several longitudinal modes of the optical cavity. The model predicts that feedback enhancement effects under strongly absorbing conditions can cause underestimations in the measured absorption, and these predictions are verified experimentally. The technique is then used in application to the detection of nitrous oxide as an exemplar of the utility of this technique for analytical gas phase spectroscopy. The analytical performance of the spectrometer, expressed as noise equivalent absorption coefficient, was estimated as 4.9 × 10 cm Hz, which compares well with recently reported values.

Laser spectroscopy for breath analysis: towards clinical implementation

“…As an example, an OF-CEAS instrument optimized for monitoring exhaled CO at 2.33 µm (4297.7 cm −1 ) offers a 0.2 ppb detection limit for CO over an acquisition time of 20 s [50]. More recently, a few OF-CEAS prototype setups in the MIR were reported based on QCL [51, 52] and lately, based on ICLs [53–55], presenting an absorption detection limit in the range of 10 − 9 cm −1 Hz −1/2 . This level of sensitivity of OF-CEAS analyzers in the mid-IR results directly from its high signal-to-noise ratio compensating for the lower detectivity of optical detectors at longer wavelengths.…”

RES-Q-Trace: A Mobile CEAS-Based Demonstrator for Multi-Component Trace Gas Detection in the MIR

“…As a proof of principle, the first application of an ICL used in an OF-CEAS measurement for the detection of methane was shown as a part of this work [ 21 ]. Successful improvements of this approach were reported recently in applying ICLs in OF-CEAS for the measurement of SO 2 and NO respectively [ 50 , 51 ].…”

Nitric Oxide Analysis Down to ppt Levels by Optical-Feedback Cavity-Enhanced Absorption Spectroscopy

“…The experimental scheme of the newly developed OF-CEAS analyzer for NO trace detection is given in Figure 1 . It is a typical set-up of an OF-CEAS analyzer, as described in several publications [ 13 , 19 , 27 , 29 , 30 ]. This instrument integrates an ICL (Nanoplus GmbH) that operates with single mode continuous wave emission and is tunable around 5.256 μm.…”