Elemental mercury sensing by synchronously sweeping two multimode diode lasers

Abstract

We propose a sum-frequency-generation (SFG) laser-based elemental mercury sensing method by mixing two low-cost multimode diode lasers (MDLs). The wavelengths of the two MDLs are synchronously scanned, which enlarges the whole coverage range of wavelength and improves the measurement stability. Correlation spectroscopy was used to eliminate the impact of environmental change and enhance and trace the absorption signal of the sample accurately. A novel data processing method was employed to extract the weak absorption signals from the background efficiently. A sensitivity of 0.1 µ g / m 3 (11 ppt) was achieved for 1-m path length and 10-s integration time. The sensing range was efficiently increased up to 200 µ g / m 3 using a calibration curve based on a new mathematical analytical formula. Real-time monitoring of the mercury volatilization and diffusion process was experimentally demonstrated with a time resolution of 10 s. The performance of the system shows great practical value for the detection of elemental mercury in industrial applications.

Primary Measurement of Gaseous Elemental Mercury Concentration with a Dynamic Range of Six Decades

“…The SPC upper detection limit (UDL) is near ρ = 1000 μg m –3 at an OD = 3 with β ρ̅ = 4 × 10 –4 . The broad dynamic range exceeds that recently reported, where a UDL of 200 μg m –3 for a 1 m absorption path was achieved using a nonlinear calibration curve. Including the short cell, the UDL for our method increases to ρ̅ = 100 mg m –3 at an OD = 2.5 and β ρ̅ = 1 × 10 –3 .…”

“…The availability of tunable lasers for probing the relatively strong 6 1 S 0 –6 3 P 1 intercombination transitions of Hg isotopes in the UV occurring near 254 nm has been exploited − as previously discussed . Lou and co-workers focused on the development of low-cost, high-throughput, and sensitive measurements of GEM using Hg-containing reference cells. ,− In contrast, a reference material-free approach, based on a first-principles spectroscopic model and measurements of the 254 nm transitions of Hg, was realized by Anderson et al They reported u r (ρ) = 6% on samples of pure GEM near room temperature, thus demonstrating the feasibility of absolute measurements using absorption spectroscopy . However, our analysis of their Hg vapor pressure measurement reveals a negative bias of ≃15% based on the weighted-average Einstein A coefficient (8.41 × 10 6 s –1 ) , and the vapor pressure correlation of Huber et al The authors note complications in their experiments including the effects of amplified spontaneous emission and nonlinearity in frequency detuning of their probe which may account for this discrepancy.…”

High Sensitivity Continuous Monitoring of Chloroform Gas by Using Wavelength Modulation Photoacoustic Spectroscopy in the Near-Infrared Range

“…In these systems, high reflection mirrors (>99.99%) are used as the window of the gas cell, and consequently the maintenance of the mirrors has always been an important issue. Non-dispersive infrared (NDIR) [12,13] and tunable diode laser absorption spectroscopy (TDLAS) [14][15][16][17][18] have also been well developed for optical gas detection over these years. Despite the relatively low stability, more and more products have been developed based on NDIR because of its low cost and fast response.…”