Multiple-pass-enhanced multiple-point gas Raman analyzer for industrial process control applications

We report an advanced multiple-pass multiple-point Raman spectroscopy setup with enhanced sensitivity for industrial in situ monitoring and process control applications. The design of this multiple sampling setup enables high laser effective energy utilization ratio, and full laser energy is available for each sampling point. As a result, high sensitivity is obtained in every sampling point. The setup is simple, reliable, and robust, which is important for practical industrial applications. With eight passes configuration, gas samples in static cells are tested to show the analytical potential of this multiple sampling setup. The back-to-back experimental results show that the noise equivalent detection limit (3 sigma) of 40.6 (N-2), 46.0 (O-2), 22.9 (H2O), and 19.1 Pa (hydrogen isotopologues), which corresponds to relative abundance by volume at 1 bar total pressure of 406, 459, 229, and 191 ppm, respectively, can be achieved in 1 s with a 1.5-W red laser. The analysis indicates that similar or even better sensitivity can be achieved for every sampling point in a practical 3-point system. The system precision is characterized by long-term measurement of static samples, and the results indicate high system stability. Although a 3-point system is demonstrated in this investigation, this setup can be easily upgraded to incorporate more sampling positions by increasing the number of lenses inside the multiple-pass cavity, which is important for practical applications. Important aspects regarding instrumentation engineering are also briefly discussed. The results obtained with this multiple-pass-enhanced multiple-point Raman system are very promising. The system can be applied to hydrogen isotopologues monitoring and process control in international thermonuclear experimental reactor (ITER), as well as China fusion engineering test reactor (CFETR). Other industrial applications like automotive engine diagnosis and logging gas detection can also be benefited from current design.