Chromatic confocal measurement method using a phase Fresnel zone plate.

Area of Science:

• Optics and Photonics
• Metrology and Measurement Science

Background:

• Chromatic confocal microscopy is a non-contact optical measurement technique.
• Traditional methods may face limitations in resolution, accuracy, or cost.

Purpose of the Study:

• To develop a chromatic confocal measurement method utilizing a phase Fresnel zone plate (FZP).
• To investigate the axial focal shift and dispersion characteristics of the FZP for metrology applications.

Main Methods:

• A phase Fresnel zone plate (FZP) with a diameter of 11.27 mm and focal length of 50 mm was fabricated using photolithography.
• Vectorial angular spectrum theory was employed for quantitative calculation of axial dispersion.
• The FZP was integrated into a homemade chromatic confocal measurement system.

Main Results:

• The FZP exhibited strong dispersion, leading to a significant axial focal shift.
• The axial dispersion curve showed near-linearity within a specific wavelength range.
• The system achieved an axial measurement range exceeding 16 mm, an axial resolution of 0.8 µm, and displacement accuracy better than 0.4%.

Conclusions:

• The developed FZP-based chromatic confocal method offers simplicity, reduced cost, and superior performance.
• The sensor has been successfully applied to measure step height, glass thickness, and 3D surface profiles.
• This sensing method holds significant potential for industrial applications in optics, electronics, and manufacturing.