Cross-period sub-nyquist sampling method for efficient 3D surface profiling in low-coherence scanning interferometry

Area of Science:

• Optical Metrology
• Surface Profilometry
• Interferometry

Background:

• Low-coherence scanning interferometry (LCSI) is a precise 3D surface profilometry technique.
• The Nyquist sampling criterion limits LCSI measurement efficiency by dictating a small sampling interval.
• Preserving signal characteristics requires adherence to strict sampling intervals, hindering speed.

Purpose of the Study:

• To propose a novel cross-period sub-Nyquist sampling method for LCSI.
• To enhance measurement efficiency without compromising signal integrity.
• To improve the accuracy and resolution of 3D surface profilometry.

Main Methods:

• Developed a cross-period sub-Nyquist sampling strategy.
• Defined a specific sampling interval based on Nyquist step size and whole wavelength cycles.
• Maintained both spatial and frequency information of the interferometry signals.

Main Results:

• Achieved a sampling interval 25 times larger than the Nyquist limit.
• Enhanced measurement accuracy by over 90% compared to random sub-sampling.
• Improved surface roughness measurement from 0.9259µm to 0.7003µm.

Conclusions:

• The proposed method significantly increases LCSI sampling intervals.
• This technique preserves essential signal characteristics, spatial, and frequency information.
• Cross-period sub-Nyquist sampling offers a more efficient and accurate approach to 3D surface profilometry.