The CASTLE telescope: on the use of curved freeform sensors for astronomical applications and beyond (Conference Presentation)

The field curvature has been a long-term problem optical designers had to deal with, to propose flat corrected field instruments. Combinations of highly aspherical optics, TMA configurations, achromatic doublets or field flatteners are often used to reach good optical quality across the image. Allowing designers to play with the parameters of the field's shape is offering them a brand-new game field. The possibility of curving the CMOS sensors to fit curved/aspherical/freeform shapes of focal surfaces has been studied for the last 20 years and led today to different applications and prototypes. We present in this article 1/ the parameter studies we performed over a large set of optical designs showing the gain offered by this approach, 2/ the CMOS sensors curving process and performance over a large set of prototypes, 3/ Optical systems that have been produced with this technology and 4/ the roadmap related to the development of curved-sensors based instrumentation for astronomy with the CASTLE telescope project and physical sciences through the Auroral UV Imager program led by ESA.