Testing of steep convex aspheric surface with a Hartmann sensor by using a CGH

Area of Science:

• Optical metrology
• Aspheric surface testing
• Precision engineering

Background:

• Traditional interferometry with null correctors struggles with highly aspheric or steep surfaces due to complex null lens/CGH design.
• 3-D profilometry is accurate but too slow for production environments.
• A need exists for rapid, accurate measurement techniques for complex aspheric optics.

Purpose of the Study:

• To adapt and validate the Hartmann test for measuring steep convex aspheric surfaces (approx. 16 mm diameter).
• To enhance measurement accuracy through CGH-based calibration of the test setup.
• To demonstrate the suitability of this method for industrial production lines.

Main Methods:

• Application of the Hartmann test to steep convex aspheric surfaces.
• Calibration of the test setup using a Computer Generated Hologram (CGH) simulating an ideal surface.
• Analysis of wavefront error (WFE) before and after calibration.

Main Results:

• The CGH calibration effectively removed significant errors in the test setup.
• Achieved a wavefront error (WFE) difference of only 2 nm rms.
• Demonstrated accuracy despite a worsened WFE of over 0.13 µm rms in the uncalibrated setup.

Conclusions:

• The calibrated Hartmann test provides a highly accurate method for measuring steep aspheric surfaces.
• This technique is significantly faster than 3-D profilometry and more adaptable than interferometry for complex optics.
• The method is suitable for implementation in manufacturing production lines due to its speed and accuracy.