25 November 2022 Optical metrology on primary mirror of visible emission line coronagraph on board Aditya-L1 mission
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Abstract

The visible emission line coronagraph (VELC) on board the Aditya-L1 mission is an internally occulted reflective coronagraph. It is capable of simultaneous observations of the solar corona in imaging, spectroscopic, and spectropolarimetric modes very close to the solar limb, to 1.05 R (R – solar radius). Primary mirror (M1) of the VELC receives the light from both the solar disk and the corona up to 3 R. In the VELC, occultation happens at the focus of the M1. Secondary mirror (M2) with a central hole size equal to 1.05 R is mounted at the focal plane of M1 and serves the purpose of an internal occulter. To meet the proposed science goals of the payload, M1 surface should be super polished with good imaging characteristics. This results in stringent requirements of the surface figure and microroughness on the mirror surface. M1 is an off-axis parabola, so achieving the demanding requirements is quite challenging. At the same time, testing of M1 after development is crucial for evaluating its performance. This paper provides the details of the optical metrology tests carried out on M1 along with the results obtained and their implications on the performance of the VELC.

© 2022 Society of Photo-Optical Instrumentation Engineers (SPIE)
Venkata Suresh Narra, Darshika Singh, Natarajan Venkatasubramanian, Vishweshwar Rao Budhiraju, Bhavana Hegde, Nishchith Bhat, Utkarsha Dasamantarao, Pawan Kumar Somasundaram, Venkateswaran Ramaswamy, Umesh Kamath Padavu, Kuppuswamy Venkatesan Sriram, and Raghavendra Prasad Budihal "Optical metrology on primary mirror of visible emission line coronagraph on board Aditya-L1 mission," Journal of Astronomical Telescopes, Instruments, and Systems 8(4), 044004 (25 November 2022). https://doi.org/10.1117/1.JATIS.8.4.044004
Received: 20 July 2022; Accepted: 3 November 2022; Published: 25 November 2022
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Cited by 2 scholarly publications.
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KEYWORDS
Mirrors

Coronagraphy

Optical metrology

Solar processes

Scatter measurement

Optical spheres

Contamination

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