The optical design and physical optics analysis of a cross-Dragonian telescope for LiteBIRD

The Lite satellite for the studies of B-mode polarization and Inflation from the cosmic microwave background (CMB) Radiation Detection (LiteBIRD) is a next generation CMB satellite dedicated to probing the inflationary universe. It has two telescopes, Low Frequency Telescope (LFT) and High Frequency Telescope (HFT) to cover wide observational bands from 34 GHz to 448 GHz. In this presentation, we report the optical design and characterization of the LFT. We have used the CODE-V to obtain the LFT optical design based on a cross-Dragonian telescope. It is an image-space telecentric system with an F number of 3.5 and 20 x 10 degrees(2) field of view. The main, near and far side lobes at far-field have been calculated by using a combination of HFSS and GRASP 10. It is revealed that the LFT telescope has good main lobe properties to satisfy the requirements. On the other hand, the side lobes are affected by the stray light that stems from the triple reflection and the direct path from feed. In order to avoid the stray light, the way to block these paths is now under study.