Starting-point design method for unobscured four-mirror reflective imagers based on multi-aberration evaluation.

Area of Science:

• Optical Engineering
• Astronomy Instrumentation
• System Design

Background:

• Confocal conic mirrors are crucial for unobscured reflective imaging systems.
• Off-axis aberrations like astigmatism, coma, and field curvature challenge system performance.
• Optimizing initial structures is vital for achieving desired imaging quality.

Purpose of the Study:

• To propose a multi-aberration evaluation function for optimizing unobscured four-mirror reflective imagers.
• To quantitatively analyze and constrain off-axis aberrations in confocal conic systems.
• To develop an optimal initial structure for high-performance space cameras.

Main Methods:

• Development of a multi-aberration evaluation function based on confocal conic mirrors.
• Quantitative calculation of typical off-axis aberrations (astigmatism, coma, field curvature).
• Application of particle swarm optimization algorithm for finding optimal configurations.
• Integration of freeform surfaces to expand the field of view (FOV).

Main Results:

• An optimal initial structure for unobscured four-mirror reflective imagers was determined.
• Simultaneous constraint of off-axis aberrations achieved excellent on- and off-axis imaging performance.
• A four-mirror space camera design was realized with specific parameters (EPD=200mm, F-number=4, FOV=4°×24°).
• High-quality imaging was achieved across visible and near-infrared (NIR) wavelengths.

Conclusions:

• The proposed multi-aberration evaluation function effectively optimizes unobscured four-mirror reflective imaging systems.
• The developed confocal conic configuration demonstrates superior imaging capabilities for space applications.
• Freeform surfaces successfully expanded the field of view, enhancing the camera's utility.