Tolerance Analysis of Wide Field of View Confocal Off-Axis Telescope System Using Freeform Mirrors for Common Optics MWIR/LWIR Sensors Onboard UAVs (Linear Astigmatism Free - Three Mirror System D70F1.4)

Linear Astigmatism Free - Three Mirror System (LAF-TMS) is a confocal off-axis system that eliminates linear astigmatism, which is the most critical aberration especially in the large field angle, and therefore, enables the telescope to have a wide field of view. Based on our experience with the telescope, we optimized the LAF-TMS for wavelength ranges of mid-wavelength infrared (3-5 mu m) and long-wavelength infrared (8-12 mu m) sensors onboard Unmanned Aerial Vehicles (UAVs). It has an entrance pupil diameter of 70 mm, a focal ratio of 1.4, and a wide field of view (FoV) of 6.20 degrees x 4.68 degrees, matching 10.9 mm x 8.2 mm sensor with 17 mu m sized pixels (LAF-TMS D70F1.4). The freeform mirrors of LAF-TMS D70F1.4 are optimized to eliminate the high order aberration. As a result, LAF-TMS D70F1.4 can achieve high-quality optical performance over a wide FoV without any additional correcting lenses. We performed the sensitivity analysis and the Monte-Carlo simulations as the feasibility study. During the sensitivity analysis and the Monte-Carlo simulation, decenter, tilt, despace, and surface RMS errors of three mirrors were analyzed. From the sensitivity analysis, we investigated 80% Energy Encircled Diameter by single factor perturbations. The system tolerance limits were calculated using the Monte-Carlo method with a normal distribution of errors. According to the results, we confirmed that the LAF-TMS D70F1.4 was feasible considering general fabrication and alignment tolerances.