Subaperture stitching for measurement of freeform wavefront

Area of Science:

• Optical metrology
• Wavefront sensing
• Freeform optics

Background:

• Accurate measurement of freeform optical surfaces is crucial for advanced optical systems.
• Traditional methods struggle with the complexity and large numerical apertures of freeform components.
• Scanning Shack Hartmann sensors (SHS) offer potential but face challenges with stitching errors.

Purpose of the Study:

• To develop and validate a robust subaperture stitching method for freeform wavefront measurement.
• To address and correct various misalignment errors inherent in scanning-based metrology.
• To enable precise characterization of complex freeform surfaces.

Main Methods:

• Dividing the wavefront into overlapping subapertures for measurement with a scanning SHS.
• Implementing a mathematical model for a stitching algorithm to connect subaperture data.
• Minimizing vertical plane errors (piston, tilt, power) within overlapping zones.
• Employing active numerical alignment to correct radial and rotational misalignments before stitching.

Main Results:

• A novel mathematical model for subaperture stitching of freeform wavefronts was developed.
• Simulation studies demonstrated the effectiveness of the proposed stitching algorithm.
• Experimental verification on a cubic phase profile freeform surface confirmed the method's accuracy.

Conclusions:

• The proposed subaperture stitching method effectively measures freeform wavefronts with high accuracy.
• The developed algorithm successfully compensates for scanning-induced misalignment errors.
• This technique provides a viable solution for metrology of complex freeform optics.