Gas spectroscopy through multimode self-mixing in a double-metal terahertz quantum cascade laser

Area of Science:

• Terahertz Spectroscopy
• Quantum Cascade Lasers
• Gas Analysis

Background:

• Self-mixing spectroscopy offers a compact approach for gas sensing.
• Expanding the frequency tuning range and optical feedback is crucial for enhanced performance.

Purpose of the Study:

• To demonstrate a multimode self-mixing terahertz-frequency gas absorption spectroscopy system.
• To improve sensing bandwidth and duty cycle compared to previous methods.

Main Methods:

• Utilized a quantum cascade laser with a double-metal device configuration for expanded frequency tuning.
• Employed a precision-micromachined external waveguide module to enhance optical feedback.
• Measured methanol spectra simultaneously using two laser modes at 3.362 and 3.428 THz.

Main Results:

• Resolved over eight absorption peaks for methanol spectra within a 17 GHz bandwidth.
• Achieved noise-equivalent absorption sensitivities of 1.20×10⁻³ cm⁻¹ Hz⁻¹/² and 2.08×10⁻³ cm⁻¹ Hz⁻¹/².
• Demonstrated significant expansion of sensing bandwidth and duty cycle.

Conclusions:

• The developed multimode terahertz spectroscopy technique enhances gas sensing capabilities.
• This approach offers a promising avenue for advanced spectroscopic analysis in various applications.