Studies On Thermoelectric Cooling Technique And Dark Noise Of CCD Detector For Spectral Analysis

Since the adaption of charge coupled device(CCD), laser Raman spectroscopy has become a more and more important detection technology in chemical analysis, which can be applied almost for all materials, no matter it is in solid, liquid or gas state. The signal of gas Raman scattering is very weak, so high sensitive CCD detector is needed for the analysis of minor constituents in gas samples. The CCD detector is sensitive to temperature, and cooling can effectively reduce the dark current noise. Therefore, how to effectively reduce the CCD temperature to reduce the dark current noise is an important topic.The lower the temperature of the CCD chip, the less the dark current. In this paper, thermoelectric cooling technology is selected to reduce the temperature of CCD. In order to improve the refrigerating efficiency of the thermoelectric cooler(TEC), we analyzed the principle of TEC and its heat-transfer characteristics in detail, and found that the temperature difference between the cool and hot terminal, and the capability of heat dissipation were the key factors to the performance of TEC. According to these factors, a set of refrigeration system has been designed. Vacuum isolation method is used to avoid water condensing. The finite element analysis software ANSYS was applied to simulate the heat conduction of the heat sink. The structure of the system was optimized according to the simulation results, and an optimized system structure was obtained. What's more, the heat exchange of gas flow in the vacuum chamber was also simulated in different pressure of buffering gas by using the FLOTRAN CFD, and the results shows that low vacuum is better for cooling because of its high flow speed and low temperature.A set of vacuum chamber for CCD detector was set up based on the designed structure. The vacuum test of the chamber was carried out with excellent air tightness. The temperature changing with the cooling time was measured in different pressure level and different kinds of buffer gases such as Ar, Ne and N2 as well as air. The experimental results show that N2 is a kind of good buffer gas for refrigerating, and higher vacuum degree does not guarantee better cooling effect. The pressure of 60 mbar or more can achieve the best effect. Besides this, the exponential decrease of dark noise with temperature is also recognized. At last, the experimental setup for gas Raman scattering was established, and the air Raman scattering signals was obtained using this setup. The results shows that reducing the temperature of CCD is good for improving its sensitivity.