Research On Mercury Gas Monitoring Technology Based On Wavelength Modulation Spectroscopy

Mercury pollution is an important part of environmental pollution.Mercury pollution is a serious threat to human health.One of the main sources of mercury pollution is caused by human activities.China is one of the countries with the most serious mercury pollution.People pay more and more attention to atmospheric pollution.In recent years,China and other relevant organizations in the world have imposed restrictions on mercury emissions.As a result,pollution has increased the demand for mercury gas monitoring technologies.The mainstream method of modern technology for mercury monitoring is based on optical methods.Optical measurement methods have the advantages of a wide measuring range and non-contact properties with respect to chemical methods.Wavelength modulation spectroscopy is a highly sensitive optical measurement method.It has the advantages of high sensitivity,low cost and small size.This dissertation mainly aims at establishing an effective monitoring method for gaseous mercury.It is of great significance to prevent and control environmental pollution,especially mercury pollution.This dissertation designed a tunable UV laser source The diode laser is a multi-mode laser with a central output wavelength of 505 nm.The wavelength of the laser is controlled by the injection current and operating temperature.At the same time,the external cavity of the grating is increased to adjust the laser wavelength to 507.3 nm which is close to the single-mode output.The 253.7 nm laser is obtained by the doubled effect of the BBO crystal on light.This dissertation This dissertation also characterizes the relationship between the diode laser's spectrum,power and injected current,and temperature.This dissertation also explored the relationship between frequency conversion energy conversion efficiency and basic frequency light.This dissertation uses wavelength modulation spectroscopy to monitor mercury gas.The laser injection current is modulated by a low-frequency sawtooth wave signal and is modulated by a high-frequency sine wave.This dissertation explores the order of the best amplitude and harmonic signal of the best amplitude and harmonic signal quality of this system.At the same time,the optimum temperature,the center current and the optimal grating angle of the laser source of this system were investigated.The signal detected by the PMT obtains harmonic signals after demodulation.The concentration of the gas to be measured is deduced based on the relationship between the harmonic signal and the mercury gas concentration.In this dissertation,the correlation spectrum technology was also used to improve the accuracy of monitoring,and the monitoring and fitting of the dual light path was completed.Gives the intensity of the absorption signal of different concentrations of mercury gas.After one hour of continuous monitoring,the system's Allan variance was counted.The sensitivity of this system has reached 40 ng/m~2.