Sub-ppm gas phase Raman spectroscopy in an anti-resonant hollow core fiber

Area of Science:

• Optical Engineering
• Spectroscopy
• Materials Science

Background:

• Raman spectroscopy is a powerful technique for gas analysis.
• Hollow core micro-structured optical fibers offer unique light-guiding properties.
• Developing sensitive and selective gas sensors is crucial for environmental monitoring and industrial safety.

Purpose of the Study:

• To demonstrate a Raman gas sensor utilizing a single cladding ring anti-resonant hollow core micro-structured optical fiber (HC-ARF).
• To optimize the HC-ARF for low attenuation and wide bandwidth in the visible spectral region.
• To enhance Raman signal detection through a novel selective core pressurization scheme.

Main Methods:

• Design and fabrication of a specialized HC-ARF for visible light operation.
• Implementation of a low power pump source (532 nm).
• Application of a selective core pressurization technique to reduce confinement loss.

Main Results:

• The HC-ARF exhibited low loss at pump and Stokes wavelengths up to 5000 cm^-1.
• Selective core pressurization improved Raman signal enhancement by a factor of 1.9.
• Direct detection of methane and hydrogen at 5 ppm and 10 ppm was achieved, respectively.

Conclusions:

• The developed HC-ARF Raman gas sensor shows significant potential for sensitive gas detection.
• The novel pressurization scheme effectively enhances Raman signal.
• A noise equivalent limit-of-detection of 0.15 ppm for methane was calculated, indicating high sensitivity.