Hybrid systems and methods for characterizing stress in chemically strengthened transparent substrates

A method of measuring first and second stress characteristics of a chemically strengthened (CS) substrate having a surface, a near-surface waveguide proximate the surface, and backing surface opposite the surface, comprising:

• applying at least one ink line to the backing surface of the CS substrate;
• operably disposing the surface of the CS substrate relative to a coupling prism assembly at a measurement location, the coupling prism assembly comprising an evanescent prism coupling spectroscopy (EPCS) coupling prism and a light-scattering polarimetry (LSP) coupling prism to respectively define adjacent EPCS and LSP coupling interfaces;
• performing a EPCS measurement of the CS substrate using the EPCS coupling interface to obtain the first stress characteristics and performing a LSP measurement of the CS substrate using the LSP coupling interface to obtain the second stress characteristics without removing either the coupling prism assembly or the CS substrate from the measurement location;
• and
• combining the first and second stress characteristics to define a full stress characterization of the CS substrate, wherein the first stress characteristics are selected from a group of first stress characteristics comprising:
• a surface compressive stress S(0), a total depth of layer DOLT, a spike depth of layer DOLsp, a knee stress CSk and a birefringence B and the second stress characteristic comprises at least one of a depth of compression DOC and a central tension CT.

A method of processing a light-scattering polarimetry (LSP) image comprising:

• forming an LSP image of a chemically strengthened (CS) substrate on a digital detector;
• processing the LSP image to form an optical retardation (OR) versus depth (D) curve of a retardation profile comprising OR data points that define first and second bend points and first and second end regions;
• determining a top window and a bottom window of the OR versus D curve by:
• determining a first derivative curve of the OR versus D curve;
• selecting a starting edge and an ending edge of the retardation profile corresponding to a first minimum and a second minimum of the first derivative curve, respectively, wherein the first region comprises depths less than or equal to the starting edge and the second region comprises depths greater than or equal to the ending edge;
• determining a curvature of the OR versus D curve;
• determining a center of mass of a left side of the curvature defining the first bend point and a right side of the curvature defining the second bend point;
• and
• the top window is defined by:
• a maximum line defined by a maximum retardation of the OR versus D curve;
• a lower line defined by a percentage of the maximum retardation of the OR versus D curve;
• the starting edge;
• and
• the ending edge;
• the bottom window is defined by:
• a minimum line defined by a minimum retardation of the OR versus D curve;
• an upper line defined by a percentage of the maximum retardation of the OR versus D curve;
• the starting edge;
• and
• the ending edge.