Dual-feedback mid-infrared cavity-enhanced absorption spectroscopy for H₂CO detection using a radio-frequency electrically-modulated interband cascade laser

Abstract

A mid-infrared cavity-enhanced sensor system was demonstrated for the detection of formaldehyde (HCO) using a continuous-wave (cw) interband cascade laser (ICL) centered at 3599 nm. A compact Fabry-Perot (F-P) cavity with a physical size of 38 × 52 × 76 mm was developed consisting of two concave mirrors with a radius of curvature of 80 mm and a reflectivity of 99.8% at 3.6 μm. Different from the widely reported electro-optical (EO) external modulation based Pound-Drever-Hall (PDH) locking technique, a radio-frequency electrical internal modulation based PDH technique was used for locking the laser mode to the cavity mode. A dual-feedback control on the laser current and on the piezo transducer (PZT) displacement was utilized for further stabilizing mode locking. A 20 m effective optical path length was achieved with a cavity length of 2 cm and a finesse of 1572. The effectiveness and sensitivity of the sensor system were demonstrated by targeting an absorption line at 2778.5 cm for HCO measurements. A linear relation between the cavity transmitted signal amplitude and the HCO concentration was obtained within the range of 0-5 ppm. A 1σ detection limit of 25 parts-per-billion (ppb) was achieved with an averaging time of 1 s based on Allan-Werle variance analysis. The reported dual-feedback RF modulation based PDH technique led to a method for gas detection using a similar experimental setup and measurement scheme.

Cavity Ring-Down Spectroscopy: Recent Technological Advancements, Techniques, and Applications

“…He et al utilized a dual-feedback RF modulation based PDH mode locking technique in combination with a cw-interband cascade laser (ICL) operating around 3.6 μm for high-sensitivity cavity-enhanced measurements of H 2 CO. They reported a detection limit (1σ) of 25 ppb with an integration time of 1 s. Ventrillard and co-workers , demonstrated the optical feedback cavity-enhanced technique with a three-mirror cavity of V-shaped geometry for two different laser systems, i.e., QCL and ICL, both operating at around 5.3 μm and reported an equivalent ppt level detection limit of NO within the acquisition time of about 150 ms.…”

Mid-Infrared Tunable Laser-Based Broadband Fingerprint Absorption Spectroscopy for Trace Gas Sensing: A Review

“…DFB-ICLs provide single mode, narrow linewidth (~0.7 MHz) [62], low power consumption (hundreds of milliwatts), a compact system solution, and RT-cw emission in the 3-6 µm range, which fill the MIR gap perfectly. DFB-ICLs have been used for the ppb-level detection of many important gases, especially hydrocarbon species [63][64][65][66][67][68][69], which leads to many important applications in various areas, for example, clinical diagnostics [70,71], combustion probing [72], environmental monitoring [73,74], and remote sensing.…”

Formaldehyde from Lignin Acidolysis Might Be Useful for In-Line Control of Industrial Biomass Processing

“…Since the formation of lignin-borne formaldehyde is facile and subject to catalytic manipulation, it is feasible that formaldehyde generation might always be associated with biomass processing that induces lignin acidolysis. Likewise, remarkable improvements in rapid and sensitive gas-phase formaldehyde quantitation have occurred because of the industrial utility and potential health concerns of this compound. , Consequently, practically significant is that in-line formaldehyde detection might serve as a control variable in large-scale processing facilities. Here, we report on initial efforts to determine if this historically controversial compound , might help enable green and sustainable industries for biomass utilization.…”