Scanning deflectometric profiler for measurement of transparent parallel plates

Area of Science:

• Optical metrology
• Surface characterization
• Precision engineering

Background:

• Accurate measurement of transparent parallel plates is crucial in optics and manufacturing.
• Traditional surface profilers face challenges with back-surface reflections from transparent materials.
• Existing deflectometric methods require refinement for enhanced precision.

Purpose of the Study:

• To enhance an angle-based deflectometric surface profiler for superior measurement of transparent parallel plates.
• To mitigate interference from back-surface reflections in transparent samples.
• To achieve high repeatability and accuracy in surface profile measurements.

Main Methods:

• Development of a modified pentamirror unit to ensure oblique incidence of the measurement beam.
• Implementation of an angle-based deflectometric technique to isolate the front surface reflection.
• Calibration and validation against established scanning deflectometric profiler systems.

Main Results:

• Successful elimination of unwanted back-surface reflections from transparent parallel plates.
• Achieved a high repeatability of less than ±0.7 nm for surface profile measurements.
• Demonstrated a measurement accuracy of approximately 3 nm over a 300 mm length using a silicon bar mirror.

Conclusions:

• The improved angle-based deflectometric profiler effectively measures transparent parallel plates with high precision.
• The modified pentamirror unit is key to overcoming back-surface reflection challenges.
• The system offers a reliable and accurate solution for demanding surface metrology applications.