The Modern Way of Refractive Index Measurement of Optical Glass at SCHOTT

The refractive index is the most important property of optical glass. Therefore, refractive index measurement is a key characterization method also for process control. The requirements for refractive index control demand a fast and accurate measurement method for production control and a very high accurate measurement method for tightest requirements. For refractive index measurement two different measurement setups are common: the V-block refractometer for economic refractive index control up to the fifths digit and the spectral goniometer Ultraviolet to infrared Refractive Index measurement System (URIS) for high precision index measurement over a broad wavelength range 185 nm to 2.325 nm up to the sixth digit. Providing Sellmeier dispersion equation data for individual measurements enables accurate interpolation of index data for arbitrary wavelengths for high precision applications. To cope with specific production requirements and the required high reliability of the measurements SCHOTT develops its own measurement setups. Both, the V-block system and the high precision spectral goniometer have been updated in recent time. SCHOTT is also participating in the standardization of refractive index measurement methods for the optical industry. In this paper the current status of refractive index measurement of optical glasses at SCHOTT is presented.