抄録
This article surveys non-destructive measurement of three-dimensional refractive index distribution, in which we calculate the distribution from complex amplitude of the light wave transmitted through or scattered by the medium to be measured. Formulas for the calculation are explained as the solution of the inverse problem for the scalar wave equation. Some approximate inverse formulas are described. They include approximations of geometrical optics, straight path, the Born and the Rytov. As their applications, measurements of distributions of air density in the aerodynamic experiments, electron density in plasmas and refractive index in optical fibers are reviewed. Brief account is also made on similar measurements with waves other than light wave. Design of a graded index lens is described as another application.
