Prism coupling methods of characterizing stress in glass-based ion-exchanged articles having problematic refractive index profiles
The prism coupling methods disclosed herein are directed to determining a stress characteristic of an original IOX article having a buried IOX region with a buried refractive index profile that is problematic in the sense that it prevents the original IOX article from being measured using a prism coupler system. The methods include modifying the buried IOX region of the original IOX article in a surface portion of the buried IOX region to form a modified IOX article having an unburied refractive index profile that allows the modified IOX article to be measured using a prism coupler. The methods also include measuring a mode spectrum of the modified IOX article using the prism coupler system. The methods further include determining one or more stress characteristic of the original IOX article from the mode spectrum of the modified IOX article.
1. A method of determining at least one stress characteristic of an original 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 original IOX article from being measured using a prism coupler system, the method comprising:
a) modifying the buried IOX region of the original IOX article in a surface portion of the buried IOX region to form a modified IOX article having an unburied refractive index profile that allows the modified IOX article to be measured using a prism coupler;
b) measuring a mode spectrum of the modified IOX article using the prism coupler system; and
c) determining the at least one stress characteristic of the original IOX article from the mode spectrum of the modified IOX article.
2. The method according to claim 1 , wherein c) comprises:
calculating a stress profile using the mode spectrum; and
determining the at least one stress characteristic of the original IOX article from the stress profile of the modified IOX article.
3. The method according to claim 2 , wherein the at least one stress characteristic comprises a surface stress, and wherein c) comprises extrapolating the stress profile through the surface portion and to the surface of the original IOX article to estimate the surface stress of the original IOX article having the buried refractive index profile.
4. The method according to claim 1 , wherein the at least one stress characteristic is selected from the group of stress characteristics comprising: a surface compressive stress, a birefringence, a compressive stress profile, a center tension, and a depth of compression.
5. The method according to claim 1 , wherein the original IOX article and the modified IOX article are frangible.
6. The method according to claim 1 , wherein the original IOX article and the modified IOX article are non-frangible.
7. The method according to claim 1 , wherein the original IOX article has a thickness TH in a range of 50 microns to 2000 microns.
8. The method according to claim 7 , wherein the original IOX article has a depth of compression DOC>0.15·TH.
9. The method according to claim 1 , wherein the modifying of the buried IOX region comprises performing a modifying IOX process.
10. The method according to claim 9 , wherein the modifying IOX process uses an in-diffusing ion selected from the group of ions comprising: Ag + , Au + , Rb + , Cs + , and Cu + .
11. The method according to claim 9 , wherein the modifying IOX process comprises immersing the original IOX article in a solution containing AgNO 3 , wherein the AgNO 3 has a concentration in the solution the range from 0.075 wt % to 1 wt %.
12. The method according to claim 1 , wherein the original IOX article comprises an aluminosilicate glass or a borosilicate glass.
13. The method according to claim 1 , wherein the buried IOX region has a depth of layer DL greater than 100 microns.
14. The method according to claim 13 , wherein the surface portion of the buried IOX region extends into the original IOX article from the surface to a depth D PS , wherein (0.05)·DL≤D PS ≤(0.5)·DL.
15. The method according to claim 1 , wherein the buried IOX region has maximum refractive index that resides below the surface at a first depth, and wherein the surface portion of the buried IOX region extends to at least the first depth.
16. The method according to claim 1 , wherein the buried IOX region is formed using either a K + —Na + IOX process or a K + —Li + IOX process.
17. 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.
18. The method according to claim 17 , wherein the IOX article is frangible.
19. The method according to claim 17 , wherein the IOX article is non-frangible.
20. The method according to claim 17 , wherein the IOX article has a thickness TH in a range of 50 microns to 2000 microns.
21. The method according to claim 20 , wherein the IOX article has a depth of compression DOC>0.15·TH.
22. The method according to claim 17 , wherein the modifying IOX process comprises immersing the IOX article in a molten solution containing AgNO 3 , wherein the AgNO 3 has a concentration in the molten solution the range from 0.075 wt % to 1 wt %.
23. The method according to claim 17 , wherein the IOX article comprises an aluminosilicate glass or a borosilicate glass.
24. The method according to claim 17 , wherein the buried IOX region has a depth of layer DL greater than 100 microns, and wherein the surface portion of the buried IOX region extends into the IOX article from the surface to a depth D PS , wherein (0.05)·DL≤D PS ≤(0.5)·DL.
25. The method according to claim 17 , wherein the buried IOX region is formed using either a K + —Na + IOX process or a K + —Li + IOX process.
26. The method according to claim 17 , further including determining the surface stress CS from a measurement of the modified surface stress CS′ via a relationship CS=F·CS′, where F is a surface stress conversion factor.
27. 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.
28. The method according to claim 27 , wherein the at least one stress characteristic is selected from the group of stress characteristics comprising: a surface compressive stress, a birefringence, a compressive stress profile, a center tension, and a depth of compression.
29. The method according to claim 27 , wherein d) comprises:
calculating a stress profile using the mode spectrum; and
determining the at least one stress characteristic from the stress profile.
30. The method according to claim 27 , wherein in the IOX article is frangible.
31. The method according to claim 27 , wherein in the IOX article is non-frangible.
32. The method according to claim 27 , wherein the IOX article has a thickness TH in a range of 50 microns to 2000 microns.
33. The method according to claim 32 wherein the IOX article has a depth of compression DOC>0.15·TH.