Vortex topographic microscopy for full-field reference-free imaging and testing.

Area of Science:

• Optics and Photonics
• Microscopy
• Nanotechnology

Background:

• Light vortices, carrying orbital angular momentum, are crucial for optical manipulation, communication, and microscopy.
• Accurate, reference-free measurement of reflective sample topography is essential for various scientific and industrial applications.

Purpose of the Study:

• To propose and demonstrate a novel full-field vortex topographic microscopy technique.
• To enable reference-free displacement and shape measurement of reflective samples with high precision.

Main Methods:

• Utilizing an array of light spots to map sample surfaces and reconstruct local depths from defocused wavefronts.
• Converting light from spots into mutually uncorrelated double-helix point spread functions (PSFs) via self-interference of optical vortices shaped by a spiral phase mask (SPM).
• Leveraging isoplanatic PSFs that maintain shape and size under defocusing for high-precision depth estimation.

Main Results:

• Demonstrated depth measurement over an 11 µm range, exceeding the microscope objective's depth of field by up to 19 times.
• Achieved surface depth mapping with better than 30 nm precision.
• Obtained lateral position precision better than 10 nm.
• Successfully profiled a bearing ball's surface and reconstructed a 3D relief of a reflection phase grating.

Conclusions:

• The developed full-field vortex topographic microscopy offers a powerful, high-precision, reference-free method for 3D surface profiling.
• The technique's ability to measure over extended depth ranges and its nanometer-level accuracy open new possibilities in microscopic surface analysis.
• Demonstrated applications in profiling complex surfaces highlight the method's practical utility.