Lens refractive index measurement based on fiber point-diffraction longitudinal interferometry

A non-immersive lens refractive index measurement method based on fiber point-diffraction longitudinal interferometry is presented. The lens imaging process is simplified to the single refraction of the back surface if the object point is located at the vertex of the front surface. The lens refractive index is derived through measuring its thickness, radius of curvature of the back surface, the distance between the object point and the image point. Experiments indicate its accuracy is better than 2.2 × 10^-4. Since the front surface is excluded in the imaging process, even an aspherical lens could be accurately measured by this method.