Precision roughness measurement of smooth surface utilizing spin-orbit interaction of light with near Brewster’s angle incidence

Roughness measurement system with nanoscale precision is limited despite the rapid advancement of surface polishing and fabrication that has reached angstrom precision. Utilizing the spin-orbit interaction, particularly the Spin Hall Effect of Light (SHEL), a novel roughness measurement is proposed. SHEL, a phenomenon of confined beam on an interface, is sensitive to the change of refractive index. On subwavelength scale the reflection of a gaussian beam with linear polarization impinged on a medium with gradient refractive index undergoes a transverse shift split. Since the shift carries the medium information, surface properties can be calculated by SHEL shift measurement and proper interface model. SHEL with weak measurement is known to experience high amplification in the incidence near the Brewster's angle which has the potential for high sensitivity measurement. In this work, we propose SHEL observation near Brewster's angle, demonstrating its potential for surface roughness measurement.