Research On Thermoelectric Cooled CCD Detector For Raman Spectroscopic Analysis

On account of the fact that the information of almost all sample molecules can be obtained in once-though operation using one excitation wavelength,Raman spectroscopy is getting more and more attention in recent years.It has become an important method in experimental studies and a standard mean of material component analysis.But the small scattering cross-sections result in feeble signal level,and bring a great challenge to the detection.With the rapid development of semiconductor and electronic technology,the performance of quantum efficiency,sensitivity,dynamic range and signal-to-noise ratio?SNR?of charge-coupled-device?CCD?detectors have been improved greatly and the CCD detectors have been widely used in Raman spectroscopy.However,the exposure time of spontaneous Raman scattering detection is usually long especially in trace gas analysis,it's necessary to take cryogenic refrigeration measures to reduce the influence of dark current noise to prevent the detected signal from being drown out by the dark current noise.On the other hand,when the dark current noise has been reduced to a negligible degree,the readout noise would dominate and become the key factor of SNR and detection limit,so it's necessary to take action to reduce the readout noise too.This dissertation aims to implement a CCD detector with low dark current noise and low readout noise,focusing on the low noise hardware system and convenient software system of the CCD detector.The home-made CCD detector was tested and evaluated for its basic functions,noise characteristics,and capability to detect spontaneous Raman scattering signals.In terms of hardware,a vacuum refrigeration structure with a two-stage thermoelectric cooler?TEC?is constructed,by which the minimum cooling temperature lowered to-32? and the difference from the ambient temperature about 47? are achieved.According to the characteristics of the refrigeration structure,the drive circuit and control circuit of the thermoelectric cooled CCD detector are designed.The ringing and crosstalk phenomena in the drive sequence are analyzed and processed,and the implementation of the low-noise DC power supply is considered.At the end,a smooth drive timing generator and a low noise DC power supply are successfully implemented.In terms of software,three functional software,including the drive sequence program,firmware program,and application program,are designed and written in very high speed integrated circuits hardware description language?VHDL?,C and C++programming language respectively.They are used to generate drive sequences,communicate with the host computer,and provide user interface.At the temperature of -30? and reading rate of 250 kHz,the peak-to-peak value of the dark field spectral readings of the home-made CCD detector is approximately 34 ADU?analog-to-digital unit?,the standard deviation is about 6.13 ADU,the dark current noise and readout noise of this detector is 0.232 e^-/?pixel·s?and 39.6 e^-rms respectively.In the Raman analysis system based on parabolic mirror gas sample cell,the spontaneous Raman scattering spectrum of ambient atmosphere was obtained by this detector,which indicates that the H₂O can be detected at the exposure time of greater than or equal to 6 s,and the SNR is 6.2.The spectral intensity of O₂,N₂ and H₂O is 2015,6309,145 ADU respectively,and the SNR is126.3,395.3 and 9.1 at the exposure time of 10 s.It shows that the home-made thermoelectric cooled CCD detector works normally and stable,and has low dark current noise and readout noise,approaching to the parameters of commercial thermoelectric cooled CCD detectors,and it can be used as a detector for weak spontaneous Raman scattering.