Diffraction gratings Interfaces (materials) Refractive index Diffraction Gratings Optical systems Anisotropy Diffractive optics Eigenvalues and eigenfunctions Electromagnetic wave diffraction Functions Index-matched interfaces Lateral displacement Light refraction Optical axis Optical correlation Refraction Vectors Wavefronts Aberrations Algorithms Anisotropic materials Approximation theory Band gaps Clinical practice Coordinate systems Correlation methods Crystals Diffractive optical elements Diffractive optical elements (DOE)