A Versatile Multiple-Pass Raman System for Industrial Trace Gas Detection.

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Industrial Monitoring

Background:

• Fast and in-line multigas detection is crucial for industrial safety and process control.
• Traditional methods may lack the sensitivity or speed required for real-time monitoring.
• Raman spectroscopy offers a non-destructive method for gas analysis.

Purpose of the Study:

• To demonstrate the effectiveness of multiple-pass-enhanced Raman spectroscopy for sensitive industrial multigas detection.
• To develop a compact and efficient optical system for enhanced gas analysis.
• To evaluate the system's detection limits and potential for multi-channel applications.

Main Methods:

• Utilized a multiple-pass optical system with D-shaped mirrors for 26 total passes.
• Employed a 1.5 W red laser for excitation.
• Configured and characterized a two-channel detection system for multi-gas analysis.
• Performed back-to-back experiments comparing single-point and multi-pass sampling.

Main Results:

• Achieved noise equivalent detection limits (3σ) of 7.6 Pa (N₂), 8.4 Pa (O₂), and 2.8 Pa (H₂O) in one second.
• Demonstrated relative volume abundances of 76 ppm (N₂), 84 ppm (O₂), and 28 ppm (H₂O) at 1 bar.
• Realized high laser energy utilization and sensitivity across sampling positions.
• Obtained comparable or improved detection limits in multi-point sampling compared to single-point systems.

Conclusions:

• Multiple-pass-enhanced Raman spectroscopy is a powerful tool for sensitive, real-time industrial multigas detection.
• The D-shaped mirror design offers a compact and efficient solution for achieving high sensitivity.
• The system's modularity allows for easy upgrades to multi-channel detection, enhancing its industrial applicability.