Spectroscopy

Quantum mechanics

Methane

Optical path

Engineering

Statistics

Materials science

Chromatography

Quantum cascade laser

Cascade

Calibration

Computer science

Acoustics

Wavelength

Path length

Absorbance

Laser

Physics

Organic chemistry

Mathematics

Optics

Electronic engineering

Allan variance

Artificial intelligence

Sensitivity (control systems)

Analytical Chemistry (journal)

Time delay and integration

Chemistry

Standard deviation

Optical path length

Noise reduction

Detection limit

Optoelectronics

Wavelet

Sensors and Actuators B Chemical

An ultra-high sensitivity sensor combining a mid-IR (MIR) interband cascade laser (ICL) at center wavelength of 3.37 μm and a multi-pass cell (MPC) with a path-length of 580 m was designed and implemented for methane detection. The ultra-high sensitivity is achieved due to the higher absorbance in the MIR than in the near infrared (NIR), a long interaction path length, and the implementation of a wavelet denoising processing algorithm. The performance of the sensor was evaluated with direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) in a series of measurements. For the sensor working in the DAS measurement mode, the optimal set of sub-wavelet functions was chosen and utilized for denoising. A calibration gas with methane concentration of 2.0 ppm was measured with a relative error of ± 1%. The minimum of the Allan deviation of the sensor of 3 ppb was achieved with an averaging time of 200 s. For the WMS technique with the Allan deviation analysis the sensor detection limit for methane of 560 ppt with 290 s averaging time was determined, which is a significant improvement compared to our DAS results and previous reports. The developed sensor has broad applicability in the high-sensitivity measurements of methane and other trace gases.

A sensitive methane sensor of a ppt detection level using a mid-infrared interband cascade laser and a long-path multipass cell