INDEX INTERFEROMETER

THE REFRACTIVE INDEX OF SCIENTIFIC MATERIALS IS OFTEN A VERY IMPORTANT PARAMETER. MANY CLASSICAL OR CONVENTIONAL TECHNIQUES FOR MEASURING INDEX OF MATERIALS REQUIRE COMPLICATED APPARATUS AND OFTEN REQUIRE SPECIAL SAMPLE PREPARATION, SUCH AS FABRICATING PRISMS OF THE MATERIAL. THIS MAY RENDER THE MATERIAL UNSUITABLE FOR USE, AS IN THE CASE WHERE IT MUST BE IN SLICES TO BE USEFUL. THIS NEW TECHNIQUE PERMITS THE DETERMINATION OF THE INDEX OF ANY SLICE OF MATERIAL, WITHOUT ANY SPECIAL SURFACE PREPARTION OTHER THAN SIMPLE POLISHING. THE TECHNIQUE IS ACCURATE TO FIVE SIGNIFICANT FIGURES AND PROVIDES THE INDEX AT ANY DESIRED WAVELENGTH, AS WELL AS A PROFILE OF THE INDEX OF THE ENTIRE SAMPLE. THE TECHNIQUE COMPARES THE FRINGE PATTERN FROM THE TOP SURFACE WITH THAT FROM A REFERENCE MIRROR TO DETERMINE THE THICKNESS. THEN, WITH THE AID OF A WHITE LIGHT SOURCE, THE INTERFERENCE PATTERN FROM THE BACK SURFACE IS COMPARED WITH THAT FROM THE FRONT TO YIELD THE OPTICAL THICKNESS OF THE SAMPLE. THE COMBINATION OF THE TWO MEASUREMENTS GIVES THE INDEX. THE BACK SURFACE FRINGE PATTERN ITSELF GIVES THE INDEX PROFILE.