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LiteBIRD is a space mission aimed at searching for the primordial gravitational waves predicted by the inflationary models of the Universe through polarization observations of the cosmic microwave background radiation. It will conduct all-sky observations from an L2 orbit in the millimeter-wave frequency range (34-448 GHz) by using two types of telescopes, the low-frequency telescope (LFT) and the mid and high-frequency telescope (MHFT). One of the challenges faced by the LFT is the issue of infrared radiation entering the telescopes. Despite the telescopes continuously avoiding the Sun and Earth, the Galactic plane cannot be avoided during their all-sky observations. While LFT filters are designed to attenuate infrared radiation, there is the possibility that the attenuation level may not be sufficient. Therefore, we are exploring the deliberate roughening of the reflector surfaces to scatter the infrared radiation on the reflector as a potential solution. There are two methods being considered for creating this rough surface. The first method involves sandblasting, which has shown the ability to selectively remove infrared radiation but poses challenges in maintaining reflector surface accuracy and ensuring uniform treatment, especially for large reflectors. The second method involves intentionally roughening the surfaces during the final machining process, causing infrared radiation to scatter due to machined grooves. The potential risk with this method is the scattering enhanced by the machined patterns, similar to a diffraction grating. In this conference, we will provide an update on the progress of these efforts.
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