A simple method to measure refractive index of optical glasses using focal displacement method

A method is presented to measure refractive index of a plane parallel plate of optical glass. We have applied focal displacement method to measure refractive index of a plane parallel plate of an optical glass having thickness of the order of millimeters. The best focus position is found by applying edge detection algorithm. We have measured LAF2 optical glass using focal displacement method and obtained the value 1.746, which is within 0.1% of the standard value 1.747 at 555 nm. In comparison to Abbe refractometer, this method is simple in terms of sample preparation, experimental set up and for measuring high refractive index of Zinc Sulfide. Using this method, refractive indices of other optical glasses are also measured.