The OptiSurf® measuring system is used for the non-contact determination of the geometric distance between two surfaces. This is calculated from the measured optical path length (OPL) and the refractive index n of the material.
d = OPL / n
The refractive index n describes the change in the speed of light of monochromatic light in a material compared to the speed of light in vacuum.
Since the refractive index is wavelength-dependent, the propagation speed of monochromatic light differs from that of spectrally broadened light. This results in the so-called group refractive index ng, which can be determined from the refractive index n, according to:
ng (λ) = n (λ) – dn (λ) / dλ
ng Group refractive index
n Refractive index