Design Of Optical Spectrometer With High Wavelength Resolution And Its Application In Temperature Determination With Emission Spectrum

Instruments for the spectroscopy are widely utilized more and more in various fields. Its main function is to test, analyze, and process the structure and composition of the material using the optics and spectral technology. The spectral characteristics of the optical signal determine the parameters of the spectrometer used for the spectrum. In this paper, a design of optimizing the wavelength resolution of spectrometer is introduced and a spectrometer in application of molecular emission spectrum is produced.In the optical structure, an improved design on optical structure of the grating spectrometer is introduced to increase the wavelength resolution. Two small lens are placed in the optical path. Compared to the traditional structure, the method not only decreases the transverse size of the entrance on the image plane of spectrometer, but also make the profile of the spectrum more clearly. Considering the type of the CCD, the relevant parameters of the CCD are analyzed to select the bigger pixel size(12um),more array size(2048×506),less exposure time(10us),with external trigger mode and thermoelectric cooling CCD.Based on the structure mentioned above, a optical spectrometer with a grating of1800L/mm has been developed. For the convenience of system debugging, a green laser is choosed as a strong light source. Electric translation stage is used to achieve precise control of the position of the collimating and focusing lens and the rotation angle of the grating. By using the spectrometer home-developed and a Charge Coupled Device camera, the lines from a hollow cathode lamp with sodium element are recorded. The experimental results show that: the wavelength resolution up to0.0559nm at wavelength range200-1100nm.Based on the diatomic molecular spectroscopy theory and Boltzmann distribution law for the equilibrium state, an improved method on the determination of the rotational temperature and vibrational temperature arc carried out with the emission spectrum from CH radicals. Both the temperatures at the inner core of an acetylene-oxygen flame at oxygen state are estimated by the emission spectrum of A-X transition of CH radicals. Firstly, the wavelength distribution and the intensity characteristics of main branches and satellite branches of A-X transition are analyzed and the corresponding required parameters to determining the temperatures are calculated and listed in the paper. Secondly, by the self-developed spectrometer with high wavelength resolution, the spectra of A-X transition from the inner core of an acetylene-oxygen flame at oxygen state was recorded and both the temperatures are estimated by the method introduced above. Therefore, it is possible to provide basic temperature data for combustion, plasma, and aerospace fields by analyzing the molecular emission spectrum.