Study on application of spectral filter in detecting stars in daytime

The limitation of star detection in daytime is poor contrast of image. Compare with the strong sky background light, star signal is so weak that can’t be detected. There are some solutions to find star signal out from strong sky background, spectral filter is selected in this article. According to the different spectrum distributions of stars and sky background, different dead wavelengths is chosen to reduce the sky background light and increase the contrast between star object and sky background. Different kinds of spectral filters were placed between adaptive optical system and secondary mirror of 1.8m telescope in Lijiang observation station. The RMS value of wavefront correction residual error and the FWHM value of far-field light spot are chosen to evaluate the correction capability of AO system. Applying spectral filter, the RMS value is improved from 0.25λ to 0.17λ and the FWHM value is improved from 0.46 arc sec to 0.34 arc sec. Both of the evaluation criterions show that spectral filter is effective for detecting stars in daytime. Furthermore, it also makes it possible to apply our adaptive optics system in daytime in future.