Hollow waveguide integrated laser spectrometer for ¹³CO₂/¹²CO₂ analysis

Area of Science:

• Optics and Photonics
• Analytical Chemistry
• Environmental Science

Background:

• Accurate measurement of carbon dioxide (CO2) isotopes is crucial for applications like medical diagnostics and climate change research.
• Existing methods for CO2 isotopologue analysis often require bulky and complex instrumentation, limiting field applicability.
• Miniaturization of laser absorption spectrometers is essential for portable and in-situ monitoring.

Purpose of the Study:

• To develop and characterize a miniaturized mid-infrared laser absorption spectrometer for precise 13CO2/12CO2 isotopologue ratio analysis.
• To demonstrate the feasibility of using hollow waveguide hybrid optical integration for compact spectrometer design.
• To assess the performance of the miniaturized spectrometer for applications requiring low sample volumes and high precision.

Main Methods:

• Hybrid optical integration using hollow waveguides to create a compact spectrometer.
• Utilizing a quantum cascade laser and integrated optical components on a single substrate.
• Analysis of hollow waveguide mode coupling and propagation for system optimization.
• Error propagation analysis from spectral inversion to calibration for performance characterization.

Main Results:

• The developed spectrometer has a compact volume (158 × 60 × 30 mm³) and requires a low sample volume (56 µL).
• Achieved a precision of 0.2‰ in 500 s integration time for isotopologue ratio analysis.
• Demonstrated an accuracy of 1.5‰, with a 0.7‰ contribution from calibrant gases.

Conclusions:

• The miniaturized laser absorption spectrometer is suitable for 13CO2/12CO2 analysis in applications such as breath analysis and geo-carbon flux studies.
• Hollow waveguide hybrid optical integration enables the development of compact, high-performance isotopic analyzers.
• Further improvements in calibration mixtures can enhance the overall accuracy of the instrument.