Improving the spectral uniformity of calibration sources for astronomical spectrographs by spectrum shaping

Calibration system is crucial for high-resolution spectrographs which are used in astronomical observation. The main scientific objective of Canary Hybrid Optical High-Resolution Ultra-Stable Spectrograph (CHORUS), under development by NIAOT, is to detect Earth-like exoplanets. The expected radial velocity (RV) precision of CHORUS is 10cm/s. Therefore, the required calibration precision is less than 10cm/s. However, the spectral intensity distributions of commonly used calibration sources vary greatly with wavelength, which reduces the signal-to-noise ratio (SNR) of calibration data. Moreover, the spectrograph detector may be saturated at some wavelengths while lacking sufficient SNR at other wavelengths. Hence, we propose a novel spectrum shaping method to improve the spectral uniformity of calibration sources and enhance the calibration precision of astronomical spectrographs. We built an experimental system based on a digital micromirror device (DMD) to demonstrate the spectral flattening of a supercontinuum source. The experimental results show that the spectral flatness is less than 0.5dB within the 585nm to738nm range.