Stray-Light Research Of Multi-Wavelength Spectrometer Of NVST

Fuxian 1m New Vacuum Solar Telescope(NVST) is the largest ground-caliber vacuum solar telescope, High-resolution imaging and observation of the solar spectrum is mainly uesed forobserving the solar photosphere and chromosphere. The influence of stray-light on the inmaging and sopectroscopic observations so far is a need to address the problem.Spectral observations, the energy accounts for a large portion of stray light spectral intensity, will have serious implications for data analysis.When observing the brightness of the target is smaller, the larger the shadow of its stray light, such as sunspot observations, the limb observations and observations of deep lines.Ground-based telescopes stray light sources are the following: 1 stray light due to the scattering of dust and particles in the Earth's atmosphere is caused; 2 due to the rapid changes in the refractive index of the atmosphere generated by the total amount of stray light on the changing;. 3. stray light generated by the instrument.We multiband spectrometer stray light from the form is divided into two categories for research: First, the instrument stray light spectrum produced by the barrel, this part of the stray light entering the light intensity spectrum barrels about, in the same incident light intensity case, this part of the stray light is constant, called this part of the stray light instrument stray light is; Second, stray light to participate in the dispersion, is the observation by the sun on the target around the sun observation targets scattering, we call this part stray light is stray light dispersion.The first stray light can be measured directly, accounting for about 3% of the energy spectrum. Because many factors affect the second stray light, it is difficult to accurately measure, from the measured spectral measurement eclipse observation around the target generated by the stray light observation target lower limit of about 10%.We discover that the left side intensity of 8556 absorption line is lower than the intensity of the remaining positions on the spectral image.We have found the reason of this phenomenon is due to the slit diffracted light directly illuminates the imaging lens.Introducted the stray-light on the CCD target surface. The intensity of stray-light is about 21.9% of the spectral image intensity.The stray-light contamination have a serious impact on spectroscopic observation.We proposes the method to eliminta thestray-light,and make the stray-light returns to normal levels.