Surface refractive index measurement method and surface stress measurement method using the same

A method of measuring a surface refractive index of a strengthened glass, the method comprising:

• a light supply process of causing light from a light source to enter a surface layer provided with a compressive stress layer of the strengthened glass through a liquid provided with a refractive index that is between a refractive index of a surface of the surface layer and a refractive index of a part of the strengthened glass deeper than the surface layer;
• a light output process of causing the light that propagates in the surface layer to be emitted toward outside of the strengthened glass through the liquid and a light input/output component;
• a light conversion process of converting two types of light components included in the light emitted toward outside of the strengthened glass into two types of emission line sequences, wherein the two types of light components respectively oscillate parallel to and perpendicular to a boundary surface between the strengthened glass and the liquid;
• an imaging process of capturing an image of the two types of emission line sequences;
• a position measuring process of measuring positions of respective emission lines of the two types of emission line sequences from the image obtained by the imaging process;
• and
• a refractive index distribution calculation process of calculating, based on a result of the measurement of the position measuring process, refractive indexes of a surface of the strengthened glass corresponding to the two types of light components, or refractive index distributions of the strengthened glass in a depth direction from the surface corresponding to the two types of light components.