Propagation of light is described as the simple harmonic motion of transverse waves. Combining waves that propagate on orthogonal planes give rise to linear, elliptical, or spherical polarization, depending on their amplitudes and phase differences. Classical experiments of Huygens and Young demonstrated the principle of optical interference and diffraction. Generalization of Fraunhofer diffraction to scattering by a three-dimensional arrangement of atoms in crystals forms the basis of diffraction methods. Fresnel diffraction finds application in the design of zone plates for X-ray microscopy. Optical microscopy, with resolution given by the Rayleigh criterion to be approximately half the wavelength, works best when tailored to the optimal characteristics of the human eye (λ = 550 nm). Lenses suffer from spherical and chromatic aberrations, and astigmatism. Optical microscopes operate in bright-field, oblique, and dark-field imaging conditions, produce interference contrast, and can image with polarized light. Variants include confocal scanning optical microscopy (CSOM). Metallography, widely used to characterize microstructures, requires polished or chemically etched surfaces to provide optimal contrast. Finally, the polarization state of light reflected from the surface of a specimen is utilized in ellipsometry to obtain details of the optical properties and thickness of thin film materials.
Effect of Nanohole Spacing on the Self-Imaging Phenomenon Created by the Three-Dimensional Propagation of Light through Periodic Nanohole Arrays