Research On Key Problems In The Practical Use Of Absorption Spectroscopy

Recently, with the advantages of high sensitivity and other merits, the technology of spectroscopy to measure is applied more and more widely.The absorption spectroscopy is based on Lambert-Beer Law. However, the Lambert-Beer Law is only applicable in ideal conditions, such as the suitable concentration of component under detection, the homogeneous light to incident and so on. And during the actual measurement, there often are many factors not to obey the restrictive conditions. In this thesis, through doing some research on the tenable conditions of Lambert-Beer law, the influences on the absorption spectrum caused by some factors like the concentration of measured material, the non-monochromatic light, the temperature, the scattering and the ingredient absorption overlap and so on are analyzed in detail.First, the affect caused by the scattering on the measurement is studied in detail. Combined with the light transport model and light scattering theory, the correctional Lambert-Beer Law is deduced when there is scattering medium in the detected substance.Secondly, the temperature change can also bring much impact on the absorption spectrum examination. In this article, aiming at the temperature affect, two different experiments are studied. One is the temperature influence on the gas absorption cross-section, in which the common pollution gases in the air SO2 and NO2 are selected as the experimental objects, and the absorption cross-section calibration formula has been given at the experimental foundation. The other is the temperature influence on the liquid absorbance, in which the glucose water is selected as the experimental object. Also, the absorbance calibration curve has been obtained in the near-infrared wave band.Thirdly in the process of spectrum examination, when there includes many kinds of material ingredient absorption in the object and the absorption overlap among different components is serious, the method of tunable diode laser absorption spectroscopy combined with data modeling is proposed to carry on the examination. Also systematic research about this method and the mathematical derivation are given.According to above findings and the certain analysis basis to the absorption spectrum principle as well as the influence factors, in view of present practical application, two sets of hardware systems are designed. The one is the differential optics absorption spectroscopy (DOAS) atmospheric environment quality monitor system and another one is continuous emission monitoring system (CEMS). In this part thorough discussion about the optical system is also made to guard against the contamination and one kind of simple mechanical structure is designed to prevent the dust dropping on the optical system in the examination.Main innovation works in this thesis mainly include:1. The correctional Lambert-Beer law is obtained using the optical transport model and the light scattering theory;2. The calibration formula and the calibration curve in view of the temperature influence to the absorption spectrum have been obtained;3. When examination material includes many ingredients and the absorption overlaps seriously one another, the method of tunable diode laser absorption spectroscopy combined with data modeling is proposed to carry on the examination4. On the basis of designing two sets of application systems, one simple mechanical structure which will replace the traditional way of blowing dry pure air onto the lens is designed to prevent the dust dropping on the optical system in the examination.