Chemically strengthened glass with a film and method for measuring surface stress of chemically strengthened glass

A chemically strengthened glass with a film, comprising:

• a chemically strengthened glass having a pair of main surfaces opposing each other;
• and
• a film formed on at least one of the main surfaces of the chemically strengthened glass,
• the chemically strengthened glass having a base composition comprising, in mole percentage on an oxide basis:
• 68.5-80% of SiO2;
• 8-20% of Al2O3;
• 0-10% of B2O3;
• 10.6-14% of Li2O;
• 2-12% of Na2O;
• 0-10% of K2O;
• 0-10% of a total content (MgO+CaO+SrO+BaO) of MgO, CaO, SrO, and BaO;
• 0-5% of a total content (ZrO2+TiO2) of ZrO2 and TiO2;
• and
• 7-20% of a total content (Li2O+Na2O+K2O) of Li2O, Na2O, and, K2O,
• wherein the chemically strengthened glass has two or less interference fringes observed under stress measurement utilizing surface propagation light having a wavelength of 365 nm, and
• the film has a refractive index lower than a refractive index of the chemically strengthened glass.