Prism coupling methods of characterizing stress in glass-based ion-exchanged articles having problematic refractive index profiles

A method of determining at least a surface stress CS of an ion-exchanged (IOX) article having a surface and a buried IOX region, the buried IOX region having a buried refractive index profile that prevents the IOX article from being measured using a prism coupler system, the method comprising:

• a) modifying the buried IOX region in a surface portion of the buried IOX region by performing a modifying IOX process while leaving a deep portion of the buried IOX region substantially unchanged to define an unburied refractive index profile having a modified surface stress CS′ different than the surface stress CS but that allows the IOX article to be measured using a prism coupler;
• b) measuring a compressive stress profile of the IOX article as modified in a) using the prism coupler system;
• and
• c) extrapolating the measured stress profile for the deep portion of the buried IOX region through the surface portion of the buried IOX region and to the surface of the IOX article to determine the surface stress CS.

A quality control method for making an ion-exchanged (IOX) article having a surface and a buried IOX region, the buried IOX region having a buried refractive index profile that prevents the IOX article from being measured using a prism coupler system, the method comprising:

• a) selecting the IOX article from a set of IOX articles formed using a common IOX process;
• b) modifying the buried IOX region of the selected IOX article in a surface portion of the buried IOX region to define an unburied refractive index profile that allows the IOX article to be measured using the prism coupler;
• c) measuring a mode spectrum of the selected IOX article as modified in b) using the prism coupler system;
• d) determining from the mode spectrum at least one stress characteristic of the selected IOX article as modified in b);
• and
• e) comparing the determined at least one stress characteristic to at least one of a target value and a tolerance for the at least one stress characteristic.