Sub-Nyquist sampling rate temporal correlation method for measuring the surface of the transparent planar element.

Area of Science:

• Optical Metrology
• Surface Metrology
• Image Processing

Background:

• Deflectometry is used for measuring transparent planar elements.
• Parasitic reflections from back surfaces cause errors in reconstruction.
• Traditional frequency-domain methods require high sampling rates (thousands of fringe patterns) to separate reflections, impacting accuracy.

Purpose of the Study:

• To develop a method for accurate surface reconstruction of transparent elements using deflectometry.
• To overcome the limitations of traditional methods regarding sampling rates and error correction.
• To improve the efficiency and accuracy of transparent surface measurement.

Main Methods:

• A novel sub-Nyquist sampling rate temporal correlation method is proposed.
• The method utilizes fewer than five hundred fringe patterns, significantly reducing data acquisition requirements.
• Temporal correlation is employed to effectively separate and mitigate parasitic reflections.

Main Results:

• The proposed method achieves accurate reconstruction of the front surface of transparent elements at a sub-Nyquist sampling rate.
• An RMS surface error of 113 nm was achieved.
• The method significantly reduces measurement time, from 1000 seconds (Wang's method) to 205 seconds, a saving of 13.25 minutes.

Conclusions:

• The sub-Nyquist sampling rate temporal correlation method offers a more efficient and accurate approach to deflectometry for transparent planar elements.
• This technique effectively addresses the challenge of parasitic reflections without compromising measurement accuracy.
• The substantial time savings demonstrate the practical applicability and advantage of this new method.