Refractive Index Measurement With High Precision by a Laser Diode Self-Mixing Interferometer

A new method based on the laser diode self-mixing interference effect for refractive index measurement is demonstrated. It employs a simple translation method to measure the optical phase shift as a function of the moving distance of the sample. The refractive index is determined by analyzing a fringe number of self-mixing signals with respect to the moving distance and the incidence angle, with an experimental accuracy of 0.004. Interestingly, the setting error of the proposed system can be effectively decreased by modifying the incidence angle. This method also shows the advantage of a large measurable range of the refractive index.