ABSTRACT
This chapter treats the refractive index as the principal measurand. The appropriate refractive index measurement technique is ellipsometry, in which the amplitude and phase of the reflected light are measured, as the polarization and the angle of incidence is varied. Some refractometric methods are essentially ellipsometric, but for transparent samples transmission methods are also important. The refractive index match method does not require the sample to be in any special shape or form. Assuming the particles to be isotropic and homogeneous, then the reflected radiance, the angular or lateral deviation, and the relative phase shift of transmitted light all become zero at refractive index match. The refractive index of individual particles large enough to image in a microscope can also be measured by the index match method. Central or oblique illumination modes can be used corresponding to the Becke and Schroeder van der Kolk methods, respectively, which utilize null deviation at refractive index match.
