Ronchi-Hartmann type null screens for testing a plano-freeform surface with a detection plane inside a caustic...

Area of Science:

• Optics and Photonics
• Optical Engineering

Background:

• Freeform optics offer advanced design possibilities but present challenges in precise characterization.
• Accurate ray tracing and wavefront analysis are crucial for understanding light propagation through complex optical surfaces.

Purpose of the Study:

• To implement an exact ray trace for a plano-freeform surface with an incident plane wavefront.
• To analyze the formation of caustic surfaces and critical points during ray propagation.
• To evaluate the shape of a plano-freeform optical surface using a novel null screen method.

Main Methods:

• Exact ray tracing through a plano-freeform surface.
• Identification and analysis of two caustic surfaces and their critical points.
• Study of refracted wavefront propagation.
• Application of a Ronchi-Hartmann type null screen for surface evaluation.

Main Results:

• Two distinct caustic surfaces were obtained from the ray tracing.
• Critical points associated with the ray tracing process were identified.
• The shape of the plano-freeform optical surface was evaluated with an RMS difference of 6.3 μm in sagitta.

Conclusions:

• The implemented exact ray trace method is effective for analyzing plano-freeform optics.
• Wavefront propagation analysis aids in understanding optical performance.
• The Ronchi-Hartmann null screen method provides accurate surface metrology for freeform optics.