大芯径光纤出射环形斑谱线分析

Analysis of Spectra Annular Spot in Large Core Fiber

光纤光谱的效率损失主要来源之一是光纤的焦比退化,并且往往还在光谱成像时因焦比退化产生环形出射斑,从而使得光纤传输效率降低,并影响色散之后的谱线轮廓。实验获取郭守敬望远镜调试阶段的大芯径光纤因焦比退化产生的出射环型斑貌,结合CCD光谱图像特点实施轮廓拟合抽谱方法,把二维CCD光谱图像转换成一维光谱,选取望远镜红端数据进行模拟,采样点在500~600 nm波段范围,在该波段中有铁的发射线。通过与获得的环形斑轮廓卷积研究焦比变化对铁发射线峰的影响。最后,正确阐明在正式巡天观测时主镜前悬挂平场漫反射屏消除环形斑引发的偏差的效果。

The introduction of optical fiber into astronomical telescope observation combined with big data technology has improved the development of astronomy. Muhi-target optical fiber measurement technology is mainly affected by the optical fiber transmittance and focal radio degradation （FRD） characteristics. During the rotation of the telescope, the fiber will be flexural deformed between the focal plane and the spectrograph, meanwhile, if the convergence center of the beam from the telescope is not aligned with the main axis of optical fiber, the FDR will be changing with it, which greatly affect the reception of the spectrograph. One of the main sources of fiber spectral efficiency loss is caused by FRD of the fiber, which often results in ring- shaped emergent image. In this paper, we obtained the ring-shaped emergent images produced by FRD of large diameter fibers in Guo Shou-Jing （LAMOST） telescope during the commissioning. According to the character CCD image, we applied spectral extraction method based on profile ftting to convert the two-dimensional CCD image into one-dimensional spectrum. We selected LAMOST spectra in wavelength range around 500-600nm, in which there were Fe emission lines. Then we studied the effect of the FRD on the Fe emission line peaks through convoluting with the obtained ring-shaped emergent profile. Finally, we discussed using flat diffuse screen before the main mirror Mb to eliminate annular plaque-induced deviation caused by the effect of ring- shaped emergent profile.