Multi-facial freeform monolith optics for astronomical and space applications

The utilization of a multi-facial freeform monolithic (MFFM) component in a compact Cassegrain configuration design offers unprecedented capabilities to accommodate various next-generation science instruments. The concept of the MFFM component can be employed for applications in telescopes working at ultra-violet, optical, infrared, terahertz, microwave, and even radio frequencies. MFFM finds its scope in space optical and astronomical systems where the risks are associated with the alignment, manufacturability, and maintaining large-sized apertures, large number of components, cost, and volume of the flight optical terminals and instruments. The current challenges faced at the manufacturing phase of MFFM are the precision positioning of each surface concerning the optical axis and maintaining the required edge thickness. This paper presents the optical design, fabrication, measurement, and in-laboratory characterization of MFFM. The results of a prototyping effort through ultra-precision single-point diamond turning (SPDT) and coating demonstrate the feasibility of producing these elements as per size and weight requirements. The experimental results show excellent surface qualities in terms of nanometric surface roughness and close-to-submicron form accuracy on each surface of the freeform monolith. Focusing performance and imaging performance are carried out to validate the designed and manufactured precision component. The main contribution is highlighted in terms of the optimized fabrication process for producing the precision MFFM for a fast optical system while balancing the alignment errors. The demonstrated research work highlights the intriguing possibilities of the monolith and creates new avenues for research in domains that use huge optical systems, such as astrophysical study, planetary observation, earth monitoring, and geosciences.