Refinement of the Duc de Chaulnes’ Image Displacement Method of Measuring Refractive Index

The Duc de Chaulnes’ image-displacement method is refined to account for errors associated with thin slices of crystals and found to give results accurate to ±0.006 in the 2.4-refractive index range. Some of the inherent errors of the method are accounted for exactly, while others are treated statistically. The method has distinct advantages in measuring n at selected sites in solids and in determining indices at ranges above those of useful immersion media. The ordinary-ray index in BaTiO3 was measured on two crystals at room temperature, and the average index determined was 2.369±0.31% (the crystal thicknesses were 0.0126 and 0.0209 cm).