Nondestructive inspection of surface nanostructuring using label-free optical super-resolution imaging

Area of Science:

• Materials Science
• Optical Physics
• Nanotechnology

Background:

• Ultrafast laser processing creates surface nanostructuring (SNS) with dimensions near the laser wavelength.
• Laser Induced Periodic Surface Structures (LIPSS) in the UV range are fascinating but difficult to characterize non-destructively due to their small size (<100 nm).
• Conventional optical microscopy is limited by diffraction, while super-resolution methods often require sample-modifying probes.

Purpose of the Study:

• To demonstrate a label-free, non-destructive optical method for characterizing sub-diffraction limit LIPSS.
• To enable in-situ monitoring and fine-tuning of laser parameters for SNS generation.
• To validate the metrological efficiency of the developed technique against Scanning Electron Microscopy (SEM).

Main Methods:

• Utilized a modified confocal reflectance microscope (CRM) operating in a photon reassignment (re-scan microscopy) regime.
• Characterized SNS, specifically LIPSS with periods from 105 to 172 nm, on a titanium sample.
• Performed label-free, non-destructive optical surface inspection at a speed of 180 µm/s.

Main Results:

• Successfully detected and characterized sub-diffraction limit LIPSS using the modified CRM.
• Achieved non-destructive, label-free imaging of nanostructures smaller than the diffraction limit.
• Demonstrated comparable results to commercial SEM, validating the technique's metrological efficiency.

Conclusions:

• The developed label-free CRM in a photon reassignment regime is effective for non-destructive characterization of sub-diffraction limit LIPSS.
• This technique offers a viable alternative to conventional methods for in-situ monitoring and control of laser-induced nanostructuring.
• The approach holds promise for advancing the fabrication of complex and hybrid nanostructures through precise laser parameter optimization.