Distance measurements by differential confocal optical ranging.

Area of Science:

• Optics and Photonics
• Metrology
• Surface Science

Background:

• Accurate distance measurement is crucial for applications in robotics, machining, and materials science.
• Traditional methods can be limited by surface properties like roughness and tilt.
• Confocal microscopy offers high-resolution depth profiling capabilities.

Purpose of the Study:

• To develop a new, highly accurate distance measurement technique using type II confocal systems.
• To improve ranging accuracy by minimizing sensitivity to surface variations.
• To demonstrate the technique's applicability for precision measurements and thin film analysis.

Main Methods:

• Utilizing the sharply peaked depth response of type II confocal systems.
• Implementing a dithering mechanism (on sample or optical system) for differential measurement.
• Generating a zero-crossing at the depth response peak to enhance accuracy.

Main Results:

• Achieved high-accuracy distance measurements independent of surface roughness or tilt.
• Demonstrated sensitivity to surface vibrations as low as 0.01 nm.
• Successfully performed thin film measurements with accuracy up to 0.04 micrometers.

Conclusions:

• The novel dithering technique significantly enhances ranging accuracy in confocal microscopy.
• This method is robust and applicable to challenging surfaces in industrial settings.
• The technique provides a powerful tool for nanoscale metrology and transparent film characterization.