Wavelength modulation‐based active laser heterodyne spectroscopy for standoff gas detection

We proposed a near‐infrared gas sensing system based on mode‐locked cavity‐enhanced absorption spectroscopy. A distributed feedback fiber laser (DFB‐FL) with a central wavelength of 1550 nm was employed as the light source, coupling with a Fabry–Perot (F‐P) cavity with an effective optical path length of 42.7 m served as the gas cell. By utilizing a homemade mode‐locked electric circuit and Pound–Drever–Hall (PDH) technique, the mode‐locking between the DFB‐FL and F‐P cavity was achieved with long‐term fluctuation of 3.2%. System performance was verified using ammonia as the analyte gas with a target line at 1550.17 nm. Allan variance analysis revealed that the minimum detection limit was 15.8 ppm with an averaging time of 216 s, corresponding to an absorption coefficient of 2.3 × 10−7 cm−1.

Section: Introductionmentioning

confidence: 99%

Near infrared ammonia sensing system based on on‐axis cavity‐enhanced absorption spectroscopy using board‐level mode‐locked circuit

Zhu,

Guan,

et al. 2024

“…Different spectroscopy techniques play an important role in the field of sensing. [1][2][3][4][5][6][7][8][9][10][11] Laser absorption spectroscopy, based on Lambert-Beer law, provides information about the type and concentration of gases by measuring the wavelength and intensity of absorption lines. 12 This detection method is less affected by cross-sensitivity among gas components compared to nonoptical methods.…”

Section: Introductionmentioning

confidence: 99%

Theoretical and experimental investigation of chalcogenide suspended waveguide gas sensor

Huang,

Wang,

et al. 2023

To address the issues of low ratio of evanescent field (γ) and high reflectivity between waveguide cross‐section and gas for the mid‐infrared waveguide sensors, we propose a chalcogenide (ChG) suspended waveguide with Ge28Sb12Se60 as the core layer and silica (SiO2) as the buffer layer. The SiO2 beneath the waveguide core ridge structure is removed to create suspended structure. The waveguide sensing performance is obtained using a 10% methane (CH4) sample. The fabricated waveguide exhibits a γ of 112%, which is a 10% improvement compared to a free‐space optical sensor with the same optical path length. The good agreement between the theoretical and experimental results of γ confirms the reliability of our theoretical investigation approach. The influences of fabrication error, environmental temperature, and pressure on sensing performances are discussed. This work provides theoretical guidance for designing waveguide structures with large γ, contributing to the further enhancement of on‐chip sensor performance.

“…15 Specifically, laser absorption spectroscopy (LAS) which utilizes the frequency-resolved fractional transmission of incident laser intensity to determine the gas properties has emerged as the preeminent choice. [16][17][18][19][20][21][22] It is based on the interaction between the laser light and the target gas molecules and is a representative technique for gas sensing. By fitting the measured spectrally resolved absorption features, calibration-free and quantitative measurements can be achieved.…”

Section: Introductionmentioning

confidence: 99%

A mid‐infrared laser absorption sensor for calibration‐free measurement of nitric oxide in laminar premixed methane/ammonia cofired flames

Jiang

Wang

et al. 2023

An interband cascade laser (ICL)‐based absorption sensor was developed for calibration‐free and high‐fidelity measurement of nitric oxide (NO) in laminar premixed methane/ammonia cofired flames using a combination of a micro‐probe and a low‐pressure, high‐temperature gas cell. The developed sensor, which has been shown to be particularly suitable for kinetic studies of ammonia combustion, used a tunable, continuous, narrow‐linewidth, free‐space ICL operating at ~5.2 μm to target the optimal NO transition centered at 1900.07 cm−1. A direct absorption spectroscopy technique with a reduced line model was implemented for calibration‐free measurements. Comprehensive experiments were first conducted to evaluate the sensor performance against the standard gas mixture at varied pressure from 20 to 101 kPa at 393 K, showing a relative difference of ≤2.5% and a measurement uncertainty of ≤2.0%. Such a sensor shows a minimum detection limit of ~2 ppm at the integration time of 1 s. The sensor was then applied for investigating the NO formation in ammonia‐methane cofiring flames with various ammonia blending ratios; the acquired experimental data was further used as benchmark data for evaluation of literature chemical mechanisms for ammonia combustion. The developed sensor system was demonstrated to be capable of providing quantitative and spatially resolved measurement of NO in ammonia‐methane cofired flames.