Development of a high-precision long trace profiler utilizing shear measurements

Area of Science:

• Optical metrology
• Precision engineering
• Surface characterization

Background:

• Deflectometric profilers face challenges with pitch error during scanning for large-scale surface measurements.
• System errors from optical imperfections significantly impact measurement accuracy.

Purpose of the Study:

• To present a novel long trace profiler (LTP) utilizing a shearing measurement technique.
• To address and compensate for pitch errors in large-scale surface shape measurements.
• To minimize system errors by maintaining a fixed distance between the optical head and the tested mirror.

Main Methods:

• Implementation of a shearing measurement technique with two independent air-bearing carriages for separate shearing and scanning movements.
• Utilizing a double shear measurement method combined with low-spatial-frequency filtering.
• Conducting simulation studies to evaluate error mitigation strategies.

Main Results:

• The double shear method with low-pass filtering effectively reduces high-frequency angular errors from air-bearing instability.
• Experimental tests on flat mirrors demonstrated measurement precision below 50 nrad root mean square (rms).
• The system design minimizes errors caused by optical device imperfections.

Conclusions:

• The developed long trace profiler with shearing technique offers a robust solution for accurate large-scale surface shape measurement.
• The system effectively compensates for pitch errors and minimizes environmental and instrumental influences.
• Achieved sub-50 nrad rms precision validates the system's performance for demanding optical applications.