Geometry Selection in Three-Mirror Freeform Imagers with an Accessible Exit Pupil

Area of Science:

• Optical Engineering
• Telescope Design
• Freeform Optics

Background:

• Reimaging telescopes feature accessible exit pupils beneficial for stray light control and optical system integration.
• Freeform surfaces enable compact, unobscured reflective systems by allowing complex folding geometries not feasible with conventional optics.

Purpose of the Study:

• To analyze the aberration correction potential of freeform surfaces in three-mirror reimaging telescopes.
• To establish a hierarchy of folding geometries for freeform reimaging telescopes based on aberration theory, without relying on optimization.
• To quantify the performance benefits of freeform optics in specific telescope folding designs.

Main Methods:

• Applied aberration theory specific to freeform surfaces.
• Evaluated and ranked various folding geometries for three-mirror reimaging telescopes.
• Compared wavefront performance of freeform systems against systems using off-axis aspheric surfaces.

Main Results:

• The ideal folding geometry for freeform optics yielded a 9x improvement in wavefront performance compared to the next best geometry.
• Within the optimal geometry, freeform optics provided a 39% enhancement in wavefront performance over off-axis aspheric designs.
• A clear hierarchy of folding geometries was established based on aberration correction potential.

Conclusions:

• Freeform surfaces offer significant advantages in designing compact and high-performance reimaging telescopes.
• Understanding the limitations and potential of different folding geometries is crucial for balancing optical and mechanical requirements in freeform telescope design.
• This study quantifies the benefits of freeform optics, demonstrating their superiority in specific telescope configurations.