Continuous monitoring of elemental mercury employing low-cost multimode diode lasers

A continuous monitoring system for elemental mercury detection utilizing low-cost multi-mode diode lasers is demonstrated. Ultraviolet light with a central wavelength at 253.7 nm is generated through sum-frequency generation. Correlation spectroscopy is employed to trace the signals of the target gas by using a reference gas cell. Algorithms including automatic peak searching and multiple-linear-regression are employed to retrieve the mercury concentration, and long term measurements are performed. For a path length of 1 m, a sensitivity of 0.12 μg m^-3 (13.4 ppt) is achieved for a 60 s integration time, and the linear dynamic range is about 0 ∼ 60 μg m^-3. Experimental results show that the present system has great potential for industrial applications.