2 X 2 Monolithic Mirror Camera Design for MID-IR

Abstract

This paper presents the design of a mid-infrared (mid-IR) 2 × 2 monolithic mirror camerahaving an entrance pupil diameter of 259 ??, a focal length of 537.253 ??, and a 1° field-of-view (FoV). This camera shows optical performance with 15 ?? spot radius of the given FoV requirements for IR array of detectors (30 ?? pixel pitch). Specifically designed for mid-IR sensing, the camera uses an IR detector with a quantum interband cascade structure of InAs/GaSb type-II superlattice (T2SL) materials, which was developed at the physics laboratory of Chonnam National University in South Korea This camera design contained only two monolithic mirrors, one consisting of two surfaces with different radius of curvature. Therefore, this design has a compact and simple structure; hence, easy to manufacture, test, and align. The optical design for the camera inspired by the Vera C. Rubin Observatory’s Large Synoptic Survey Telescope (LSST), an improved Paul-Baker three-mirror system with three refractive lenses and a color filter. Considering the need to add cooling and signal processing equipment behind the detector, we decided to modify the design to add a quaternary mirror instead of the camera lenses. To determine tolerances, M2/M4 mirror substrate was misaligned, and the direction of maximum error was measured. As a result, in the range of 30 ?? RMS spot radius for the three DoF, the calculated tolerances were 0.4° for X-rotation, 0.17 ?? for Y-translation, and 0.03 ?? for Z-translation. This outcome confirmed that Z-translation is the most sensitive of the three.