When a focused beam with a Gaussian profile impinges a surface, the reflected beam is sensitive to a macroscopic wavelength Λ = Λ (Δz,ω0,n), where Δz is the out-of-focus distance, ω0 is the diameter of the beam in the focal region, and n is the index of refraction of the media. However for n = const, we have found that Λ = const, certifying such optical surface height measurements. The phase variations of the reflected beam were calculated for changes in the complex index of refraction for several metals and dielectric materials, demonstrating the possibility of distinguishing between various metals when their surface profiles are below the measuring limit of the instrument.
© 1988 Optical Society of America
Jacob Politch and Dan Pantzer, "Influence of a converging incident beam and variations in the surface complex index of refraction on optical profilometric measurements," Appl. Opt. 27, 3185-3189 (1988)