Prism Coupling Methods With Improved Mode Spectrum Contrast for Double Ion-Exchanged Glass

A method of characterizing a compressive stress of a double ion-exchanged (DIOX) glass sample having a surface and a base refractive index ns, comprising:

• wetting either a coupling surface of a coupling prism of refractive index np or the DIOX sample surface with an interfacing fluid having a refractive index nf;
• interfacing the coupling prism to the surface of the DIOX sample to define a prism-sample interface having input and output ends, with the interfacing fluid residing between the coupling prism and the DIOX sample surface, wherein nf differs from np by no more than 0.03, and wherein the sample has a refractive index profile with a region adjacent the surface that satisfies
• 0.0004
• ≤
• 
• λ
• n
• 
• 
• n
• 
• x
• 
• ≤
• 0.0013
• ,
• where λ is a wavelength of measuring light;
• illuminating the prism-sample interface with the measurement light, wherein a portion of the measurement light at the input end of the prism-sample interface is either partially or completely blocked;
• digitally capturing TE and TM mode spectra reflected from the prism-sample interface;
• and
• processing the TE and TM mode spectra to determine the compressive stress of the DIOX sample.

A method of characterizing a compressive stress of a double ion-exchanged (DIOX) glass sample having a surface and a base refractive index ns, comprising:

• wetting either a coupling surface of a coupling prism of refractive index np or the DIOX sample surface with an interfacing fluid having a refractive index nf;
• interfacing the coupling prism to the surface of the DIOX sample to define a prism-sample interface, with the interfacing fluid residing between the coupling prism and the DIOX sample surface, wherein nf differs from np by no more than 0.03, and wherein the sample has a refractive index profile with a region adjacent the surface that satisfies
• 0.0004
• ≤
• 
• λ
• n
• 
• 
• n
• 
• x
• 
• ≤
• 0.0013
• ,
• where λ is a wavelength of measuring light;
• directing the measuring light through a first diffuser and then through an input surface of the coupling prism and then through the interfacing fluid into the substrate surface, wherein the first diffuser is spaced apart from the input surface by 4 cm or less;
• digitally capturing TE and TM mode spectra reflected from the prism-sample interface;
• and
• processing the TE and TM mode spectra to determine the compressive stress of the DIOX sample.

A method of capturing improved-contrast mode spectra of a double ion-exchanged (DIOX) glass sample having a surface with a refractive index n0 and a base refractive index ns, comprising:

• wetting either a coupling surface of a coupling prism or the DIOX sample surface with an interfacing fluid having a refractive index nf;
• interfacing the coupling prism of refractive index np to the surface of the DIOX sample to define a prism-sample interface, with the interfacing fluid residing between the coupling prism and the DIOX sample surface, wherein nf differs from np by no more than 0.03, and wherein the sample has a refractive index profile with a region adjacent the surface that satisfies
• 0.0004
• ≤
• 
• λ
• n
• 
• 
• n
• 
• x
• 
• ≤
• 0.0130
• ,
• where λ is a wavelength of measuring light;
• directing the measuring light through a first diffuser and through an input surface of the coupling prism and then through the interfacing fluid into the substrate surface to cause the measuring light to reflect from the prism-sample interface, wherein the first diffuser is located within 4 cm of the input surface;
• and
• capturing the reflected light with a digital detector to digitally capturing TE and TM mode spectra having a first contrast that is at least 10% greater than a contrast formed when the same DIOX sample is measured using a conventional method where nf is greater than the sample surface index n0 by no more than about 0.12.