Measurement of the refractive index of glass with 10−4 level accuracy based on the lateral displacement method

The measurement of the refractive index of optical glass samples is a common and fundamental activity in numerous fields of expertise. Several measurement techniques exist with relative accuracies from 10 − 2 to, at least, 10 − 7 with complexities that are inversely related to the corresponding uncertainty. We describe an implementation of a technique based on the measurement of the lateral displacement variation of a collimated beam caused by the rotation of a parallel plate glass sample. The method was aimed to achieve an uncertainty in the range from 10 − 3 to 10 − 4 without increasing the complexity normally associated with techniques with this level of accuracy. The system was designed and optimized based on a detailed analysis of the uncertainty budget. We describe the implementation, the data processing, and the results obtained with calibrated samples, showing a relative uncertainty at the level of 10 − 4.