Long wavelength mid-infrared multi-gases spectroscopy using tunable single-mode slot waveguide quantum cascade laser

Area of Science:

• Optoelectronics
• Spectroscopy
• Environmental Science

Background:

• Quantum cascade lasers (QCLs) offer tunable mid-infrared (MIR) emission for sensitive gas sensing.
• High-resolution trace gas detection is crucial for environmental monitoring and industrial applications.
• Extending QCLs to longer MIR wavelengths (>12 µm) enables detection of various important molecules.

Purpose of the Study:

• To develop a tunable, single-mode slot waveguide QCL array operating in the long-wavelength MIR region (>12 µm).
• To demonstrate the capability of the QCL array for high-sensitivity individual and multi-species trace gas detection.
• To validate the performance of the QCL array against theoretical predictions for acetylene and o-xylene.

Main Methods:

• Fabrication of a tunable single-mode slot waveguide QCL array.
• Characterization of the laser array's tuning range and spectral properties.
• Gas sensing experiments using laser absorption spectroscopy for acetylene and o-xylene, both individually and as a mixture.

Main Results:

• The developed QCL array demonstrated a tuning range of approximately 12 cm^-1 (735.3–747.3 cm^-1).
• Achieved detection limits of 940 ppb for acetylene and 470 ppb for o-xylene.
• Multi-species gas sensing of acetylene and o-xylene mixtures showed excellent agreement between measured and predicted absorption features.

Conclusions:

• The tunable single-mode QCL array is a viable technology for high-resolution, high-sensitivity trace gas sensing in the long-wavelength MIR.
• The QCL array shows significant potential for both single and multi-gas detection applications.
• The demonstrated performance validates the QCL array's suitability for accurate atmospheric and industrial gas analysis.