Hybrid diffractive-refractive lens for chromatic confocal measurement system

Area of Science:

• Optics and Photonics
• Optical Metrology
• Nanofabrication

Background:

• Chromatic confocal microscopy (CCM) is a non-contact optical technique for surface profiling.
• Traditional CCM systems often face challenges with optical system size and linearity of chromatic dispersion.

Purpose of the Study:

• To introduce a novel CCM method employing a hybrid diffractive-refractive lens.
• To optimize chromatic dispersion linearity and reduce the overall size of the optical system.

Main Methods:

• Designed and fabricated a hybrid diffractive-refractive lens by etching a diffractive surface onto a quartz aspheric lens using lithography.
• Integrated the hybrid lens as a dispersive objective in a CCM experimental setup.
• Calibrated the system using a laser displacement interferometer.

Main Results:

• Achieved high linearity (R²=0.9999) in wavelength-to-axial position coding within the 500-700 nm range.
• Demonstrated an axial resolution of 0.08 µm.
• Reported a displacement measurement nonlinear error below 2.05 µm.

Conclusions:

• The hybrid diffractive-refractive lens effectively enhances CCM system performance.
• This novel approach offers a compact and highly linear solution for precise optical measurements.