Light source intensity control system and method for improved light scattering polarization measurement

Abstract

This invention discloses a system and method for performing stress measurement on chemically strengthened glass [10] using a light scattering polarization measurement system [200]. The method includes: adjusting the intensity of a light beam [216] from a light source [212] in an illumination system [210] using a rotatable half-wave plate [500] and a first polarizer [600]. The rotatable half-wave plate [500] and the first polarizer [600] are operably positioned between the light source and a point having a rotation time t. R Between the rotating light diffuser [222]. The first polarizer is positioned [P] by rotating the rotatable half-wave plate to a position [P] aligned with the second polarizer [232] in the downstream optical compensator [230] to have a matching polarization direction, at which the exposure time tE falls within the exposure range t. R ≤t E The method also includes using the exposure time t. E An exposure is performed to obtain the stress measurement. One or both of the half-wave plate and the first polarizer may be tilted to prevent harmful back-reflected light [R1, R2, R3, R4] from entering the light source.

Description

[0001] This application claims priority to U.S. Provisional Application Serial No. 63 / 169,466, filed April 1, 2021, the contents of which are incorporated herein by reference in their entirety.

[0002] This invention relates to a light scattering polarization measurement system for measuring stress in glass, and more particularly to a system and method for controlling the intensity of a light source in the light scattering polarization measurement system to achieve improved stress measurement on a range of different types of chemically strengthened glass. Background Technology

[0003] Chemically strengthened (CS) glass is formed by subjecting glass to chemical modification to improve at least one strength-related property, such as hardness and shatter resistance. CS glass has been found to have specific uses as cover glass for display-type electronic devices, particularly handheld devices such as smartphones and tablets. One form of chemical strengthening involves exchanging ions in the glass with external ions, and this process is referred to in this technology as ion exchange, or simply IOX.

[0004] Chemical strengthening processes introduce stress into CS glass. This stress causes CS glass to possess enhanced strength-related properties, such as increased hardness and greater shatter resistance. Therefore, an important aspect of manufacturing CS glass is characterizing the stress within it to ensure that an optimal or selected amount of stress is introduced into the CS glass, thereby giving it optimal or selected strength-related properties.

[0005] One type of glass stress measurement method is called optical scattering polarization measurement, or simply LSP. In an LSP system, CS glass is irradiated by an input laser at a relatively shallow angle through a coupling prism. The laser polarization is continuously varied between different polarization states using an optical compensator. The scattered light is detected by an image sensor. The stress in the CS glass causes optical retardation along the optical path, where the stress is proportional to the derivative of the optical retardation. The amount of optical retardation can be determined from the stress-induced phase shift of the intensity distribution of the detected scattered light at each depth along the beam path. The LSP method can be used to measure certain stress-related properties, such as central tension (CT) and depth of compression (DOC). An example of an LSP system is combined with an evanescent prism-coupled spectroscopy (EPCS) system to form a hybrid glass stress measurement system as disclosed in U.S. Patent Application No. 63 / 152,021, filed February 22, 2021, which is incorporated herein by reference. Hybrid systems offer the following advantages: they enable two complementary types of stress measurements, resulting in a more complete and accurate characterization of the stress properties of CS glass (e.g., surface stress, near-surface compressive stress distribution, knee stress, layer depth, center tension, compression depth, etc.).

[0006] The LSP system is used to measure different CS glass types with varying amounts of light scattering. Problems arise when a single photosensor with a fixed integration time exists, and when the light source intensity cannot be controlled to provide the optimal amount of light for measuring the stress of a given CS glass type. This situation leads to inconsistent stress measurements and inaccurate stress characterization across different types of CS glass. Summary of the Invention

[0007] Embodiments of this disclosure relate to a method for performing stress measurements on chemically strengthened glass using an LSP system, the LSP system having a light source system for emitting a light beam, an optical compensator, and an integration time t. I The digital detector, the method comprising the steps of: a) adjusting the intensity of a light beam by aligning a first polarizer with a second polarizer in the optical compensator to have a matched polarization direction using a rotatable half-wave plate operably disposed between the light source and a rotating light diffuser, the rotating light diffuser having a rotation time t R By rotating the rotatable half-wave plate to the exposure time t E Falling within the exposure range R ≤t E a) Achieve alignment using the position within the range; b) Use the exposure time tE Perform exposure to obtain the stress measurement.

[0008] Another embodiment of this disclosure includes the above method, wherein the chemically strengthened glass comprises a first chemically strengthened substrate having a first amount of light scattering, and further includes the steps of: replacing the first chemically strengthened substrate in the LSP system with a second chemically strengthened substrate having a second amount of light scattering, the second amount of light scattering being at least twice that of the first amount of light scattering; and repeating operations a) and b) on the second chemically strengthened substrate.

[0009] Another embodiment of this disclosure includes any of the above methods, wherein the adjustment includes measuring the contrast of the intensity distribution of the LSP image captured by the digital detector.

[0010] Another embodiment of this disclosure includes any of the above methods, wherein the exposure time t E Between 5ms and 10ms.

[0011] Another embodiment of this disclosure includes any of the above methods, wherein the light source system includes the light beam along an axis of its travel, wherein the rotatable half-wave plate and the polarizer form back-reflected light from the light beam, and further includes the step of: operably tilting at least one of the rotatable half-wave plate and the first polarizer relative to the axis to avoid directing the back-reflected light to the light source.

[0012] Another embodiment of this disclosure includes any of the above methods, wherein back-reflected light is directed to one or more light absorbers.

[0013] Another embodiment of the present invention includes any of the above methods, wherein the rotatable half-wave plate has a tilt angle θ relative to the axis. WP The tilt angle θ WP In 10°≤θ WP Within the range of ≤20°.

[0014] Another embodiment of this disclosure includes any of the above methods, wherein the polarizer has a tilt angle θ relative to the axis. P The tilt angle θ P In 5°≤θ P Within the range of ≤10°.

[0015] Another embodiment of this disclosure includes any of the above methods, wherein the light source comprises a laser diode having an optical power in the range of 20 to 300 milliwatts.

[0016] Another embodiment of this disclosure includes any of the above methods, wherein the rotating light diffuser includes a holographic light diffuser.

[0017] Another embodiment of this disclosure includes any of the above methods, wherein the second polarizer includes a polarization beam splitter.

[0018] Another embodiment of the present invention includes any of the above methods, further comprising rotating the rotatable half-wave plate by means of an electrically driven mounting bracket operably supporting the rotatable half-wave plate.

[0019] Another embodiment of this disclosure includes any of the above methods, wherein the rotation of the rotatable half-wave plate is performed using a controller configured to automatically operate the motorized mounting bracket.

[0020] Another embodiment of this disclosure includes any of the above methods, wherein the half-wave plate comprises a polymer material.

[0021] Another embodiment of this disclosure includes any of the above methods and further includes the steps of: forming a digital LSP image of the chemically strengthened glass on a digital detector having a saturation limit and including pixels having corresponding pixel intensities as defined by the digital LSP image; and wherein adjusting the intensity of the light beam includes limiting the pixel intensity to between 25% and 75% of the saturation limit.

[0022] Another embodiment of this disclosure relates to an illumination system that provides light intensity control in an LSP system used for measuring stress in chemically strengthened glass, the illumination system being coupled with a compensator and having an integration time t I The digital detector optical communication. The illumination system includes the following components arranged sequentially along an axis: a light source that emits a light beam along the axis with a first intensity; a rotatable half-wave plate; a first polarizer having a first polarization direction aligned with a second polarization direction of a second polarizer in the optical compensator; and a rotatable light diffuser having a rotation time t. R Furthermore, the rotatable half-wave plate is configured at a rotation angle such that the light beam exiting the first polarizer and incident on the rotatable light diffuser has a second intensity lower than the first intensity, such that the LSP system has an exposure time t for the CS glass. E The stress in the CS glass is measured, and the exposure time falls within the exposure range, t R ≤t E Inside.

[0023] The lighting system described above, wherein the rotatable half-wave plate and the polarizer form back-reflected light, and wherein at least one of the rotatable half-wave plate and the polarizer is operably tilted relative to the axis to guide the back-reflected light to the light source.

[0024] In any of the lighting systems described above, the rotatable half-wave plate has a tilt angle θ relative to the axis. WP The tilt angle θ WP In 10°≤θ WP Within the range of ≤20°.

[0025] A lighting system as described in any of the above lighting systems, wherein the polarizer has a tilt angle θ relative to the axis. P The tilt angle θ P In 5°≤θ P Within the range of ≤10°.

[0026] A lighting system such as any of the above lighting systems, wherein back-reflected light is directed to one or more light absorbers.

[0027] A lighting system as described in any of the above lighting systems, wherein the exposure time t E It is between 5ms and 10ms.

[0028] A lighting system as described in any of the above lighting systems, wherein the light source comprises a laser diode having an optical power in the range of 20 to 300 milliwatts.

[0029] The lighting system described above includes any of the lighting systems described above, wherein the light diffuser includes a holographic light diffuser.

[0030] The lighting system is any of the lighting systems described above, wherein the second polarizer includes a polarization beam splitter.

[0031] The lighting system, as described in any of the above lighting systems, further includes a rotatable motor mounting bracket that rotatably supports the rotatable half-wave plate.

[0032] The lighting system, such as any of the lighting systems described above, further includes a controller configured to automatically operate the rotatable motorized mounting bracket.

[0033] The lighting system of any of the above lighting systems, wherein the half-wave plate comprises a polymer material.

[0034] The lighting system, such as any of the lighting systems described above, further includes an optical compensator.

[0035] Additional features and advantages are set forth in the following detailed description, and the description will be obvious to those skilled in the art, or may be recognized by practice of the embodiments described in the draft specification and claims and the accompanying drawings. It should be understood that both the foregoing general description and the following detailed description are exemplary only and are intended to provide an overview or framework for understanding the nature and character of the claims. Attached Figure Description

[0036] The accompanying drawings are included to provide a further understanding. The drawings are incorporated in and form part of this specification. The drawings illustrate one or more embodiments and, together with the detailed description, serve to explain the principles and operation of various embodiments. Therefore, this disclosure will be more fully understood from the following detailed description in conjunction with the accompanying drawings:

[0037] Figure 1 This is a schematic diagram of an example LSP system with a light source system, which includes a rotating half-wave plate and a polarizer operably positioned upstream of a diffuser and between a laser source and a first focusing lens.

[0038] Figure 2A for Figure 1 A close-up view of the light source system of the LSP system.

[0039] Figure 2B The example is a front view of a rotatable half-wave plate, showing the measurement of the half-wave plate angle φ relative to a reference position in the light source system.

[0040] Figure 3 and Figure 4 For different inspection orientations Figure 1 Additional schematic diagram of an example LSP system.

[0041] Figure 5 This is a schematic diagram of a characteristic X-shaped LSP image formed on a digital detector of an LSP system.

[0042] Figure 6 This is a graph showing the combined intensity I(φ) (arbitrary units, au) of an example LSP image with a diffuser (square) but without a diffuser (circle) versus the half-wave plate angle φ (degrees) of the half-wave plate (in the case of no polarizer in the light source system).

[0043] Figure 7A and Figure 7B Example LSP images of an example glass-ceramic substrate obtained under two orientations of a half-wave plate spaced 45 degrees apart, for an LSP system using the light source system described above but without a polarizer.

[0044] Figure 8A and Figure 8B Similar to Figure 7A and Figure 7B Furthermore, this is an example LSP image of a glass-ceramic substrate obtained using a light source system including a half-wave plate and a polarizer as described above, under two orientations of the half-wave plate spaced 45 degrees apart.

[0045] Figure 8C Similar to Figure 7A and Figure 8A It is for example CS substrates that do not have as much light scattering as CS glass-ceramic substrates, and shows a central light spot or "fireball" as well as the bright ends of the line image.

[0046] Figure 9 The graph is a composite intensity I(φ) (arbitrary units) of the integrated intensity I(φ) of the half-wave plate angle φ (degrees) of the half-wave plate in the light source system, based on data collected using a 50-mW laser source for various half-wave plate angles φ. The graph shows the substantial deviation from the model prediction due to back reflection and the contrast that varies with the half-wave plate angle φ. The dashed lines show the ideal or expected peaks and valleys in the absence of back reflection.

[0047] Figure 10 Similar to Figure 2A An embodiment of the light source system is shown, in which the rotatable half-wave plate and polarizer are tilted relative to axis A1.

[0048] Figure 11 for Figure 10 A close-up view of the tilted half-wave plate assembly of the light source system.

[0049] Figure 12 for Figure 10 A close-up view of the tilted polarizer of the light source system.

[0050] Figure 13 The graph shows the output optical power P (mW) versus the half-wave plate angle φ (degrees) under the following configurations: no tilt of the half-wave plate and polarizer (triangle, curve A), only tilt of the half-wave plate (curve B), and both tilted (curve C).

[0051] Figure 14 To and Figure 13 The same curve as in [the previous section], but for polymer-based half-wave plates instead of [the previous section]. Figure 13 Quartz-based half-wave plate.

[0052] Figure 15 Similar to Figure 9 However, both the half-wave plate and the polarizer are operablely tiltable in the light source system. Detailed Implementation

[0053] Various embodiments of this disclosure are now described in detail, examples of which are illustrated in the accompanying drawings. Wherever possible, the same or similar reference numerals and symbols throughout the drawings refer to the same or similar parts. The drawings are not necessarily drawn to scale, and those skilled in the art will recognize that the drawings have been simplified to illustrate key aspects of this disclosure.

[0054] Cartesian coordinates are used for reference in some of the accompanying drawings and are not intended to be limited to direction and / or orientation.

[0055] The abbreviation μm stands for micrometer, and a micrometer is 10-1 -6 rice.

[0056] The abbreviation nm stands for nanometer, and a nanometer is 10 -9 rice.

[0057] As used herein, the term "glass" includes common glass, glass crystals, or glass ceramics. Similarly, the term "glass substrate" can include glass articles, glass parts, glass assemblies, etc. In some cases, the term "glass ceramic" is used to specifically refer to glass ceramic substrates, articles, etc.

[0058] The abbreviation CS stands for "chemical fortification" unless otherwise stated.

[0059] The terms "upstream" and "downstream" refer to positions relative to the direction of light travel. "A upstream of B" means that light first enters A and then enters B, and "A downstream of B" means that light first enters B and then enters A.

[0060] The term "lens," as used herein, can refer to an assembly of optical components or a single optical component. Similarly, an optical component can be a refractive, reflective, or diffractive component, unless otherwise specified.

[0061] The “optical path” of an optical system refers to the path by which light travels through the optical system from one location to another, and is considered an inherent property of the optical system as defined by its constituent elements, i.e., the optical path still exists even when no light is traveling through the optical system.

[0062] The term "contrast" used in the following section regarding intensity distribution can be expressed as C = [I IMAX -I MIN ] / [I IMAX +I MIN ], where I IMAX and I MIN These represent the maximum and minimum values ​​in the intensity distribution.

[0063] In the following discussion, the term “tilt” as used in conjunction with the rotatable half-wave plate 500 and the polarizer 600 means operatively tilted, i.e., tilted in a manner that reduces or eliminates back reflections that do not reach the output end face of the light source 212, as discussed below.

[0064] The following text discusses the rotation time t used by the rotating light diffuser. R It is the time it takes for the rotating light diffuser to complete one full rotation.

[0065] The LSP system described in this article can also be called a light scattering polarimeter.

[0066] It will be apparent to those skilled in the art that various modifications may be made to the preferred embodiments of the present disclosure as described herein without departing from the spirit or scope of the present disclosure as defined in the appended claims. Therefore, the present disclosure covers the modifications and variations provided, which are within the scope of the appended claims and their equivalents.

[0067] LSP system

[0068] Figure 1 This is a schematic diagram of an example LSP system 200 including a light source system 210 according to the present disclosure. Figure 3 and Figure 4 For different inspection orientations Figure 1 Additional schematic diagram of example LSP system 200. LSP system 200 includes system axes A1 and A2, which may be referred to as the first axis and the second axis, or simply axis A1 and axis A2, respectively.

[0069] Light source system 210 includes a light source 212 that emits light (or a beam) 216 traveling along an optical path OPL. In an example, light source 212 consists of or contains a laser. In an example, light source 212 includes a laser diode, which in this example further operates at λ = 405 nm. The example laser diode can produce optical power ranging from 20 mW to 300 mW. The wavelength λ may be referred to as the LSP wavelength. Light source system 210 is described in more detail below.

[0070] LSP system 200 also includes an optical compensator 230, which resides in the optical path OPL and downstream of the light source system 210 along the (folded) axis A1. The optical compensator 230 includes a polarizer 232, which may be in the form of a polarization beam splitter (PBS). The polarizer 232 has a polarization direction. The optical compensator 230 also includes a half-wave plate 234H and a quarter-wave plate 234Q, one of which can be rotated relative to the other to change the polarization state of the beam 216. In this example, the optical compensator 230 may include an electronically controlled polarization modulator, such as a liquid crystal modulator or a ferroelectric liquid crystal modulator or similar modulator, which will constitute or otherwise include the "polarizer" in the optical compensator 230.

[0071] In the example, the optical compensator 230 is operatively connected to the controller 400 (see [link]). Figure 3 and Figure 4 The controller 400 controls the polarization switching operation performed by the optical compensator. In one example, the optical compensator 230 may comprise a single liquid crystal device. In another example, the optical compensator 230 may comprise multiple elements, such as polarizers, waveplates, filters, prisms (e.g., wedge prisms), etc. In one example, the optical compensator 230 causes the beam 216 to pass through a full polarization cycle (i.e., changing between two or more selected polarizations) anywhere from less than 1 second to 10 seconds. In one example, the optical compensator 230 may be operatively connected to and controlled by the system controller 400. A focusing lens 236 resides downstream of the optical compensator 230 in the optical path OPL and is used to form a focused beam 216F. The optical compensator 230 and the focusing lens 236 constitute an optical modulation system.

[0072] LSP system 200 includes an LSP coupling prism 42 residing downstream of focusing lens 236. The LSP coupling prism has a separate input surface 43 and output surface 44, and a bottom or "coupled" surface 45. The coupling surface 45 and top surface 12 of the CS glass substrate 10 define an (LSP) coupling interface INT. In this example, the coupling interface INT includes a refractive index matching fluid 5 (see [link to documentation]). Figure 3 The CS glass substrate 10 has a body 11 and a bottom surface 14 opposite to the top surface 12.

[0073] Detector system 240 resides downstream of the LSP coupling prism and along an optical path OPL on the (second) axis A2, which is orthogonal to the (first) axis A1, i.e., axis A2 resides in the YZ plane. In this example, detector system 240 includes a collection optics system 243 and a digital detector (e.g., a CDD camera) 246. In this example, the collection optics system 243 is telecentric and has unity magnification. Detector system 240 may also include a bandpass filter 244 centered on the LSP wavelength λ. Figure 4 In the best-performing example, the digital detector 246 comprises an array of imaging pixels 247, which in this example may have a size between 1.8 micrometers and 10 micrometers. If the exposure time is not set to be proportional to the intensity of the received signal, the digital detector 246 suffers from sensor saturation, as discussed below.

[0074] In the general operation of the LSP system 200, a focused beam 216F formed by the focusing lens 236 is incident on the input surface 43 of the LSP coupling prism 42 and travels to the coupling surface 45, then through the refractive index-matched fluid 5 and to the top surface 12 of the CS substrate 10, entering the body 11 of the CS substrate. The focused beam 216F has selective polarization at any given time, as defined by the optical compensator 230. The (polarized) input focused beam 216F is scattered by particles in the body 11 of the CS substrate 10 to form a scattered beam 216S. The scattered beam 216S detaches from the top surface 12 of the CS substrate, travels back through the coupling interface INT, and then detaches from the coupling prism 42 at the output surface 44. The scattered beam 216S travels to the detector system 240 and is guided by the collecting optics system 243 to the digital detector 246. The scattered beam 216S forms an LSP image 248 on the digital detector 246, such as... Figure 5 The close-up view shown. This defines a digital LSP image. LSP image 248 is considered a digital LSP image unless otherwise stated. Figure 5 The schematic diagram of example LSP image 248 shows a line image LI forming a characteristic “X” shape due to the reflection of scattered beam 216S from different interfaces associated with interface INT, such as those defined by CS substrate 10, LSP coupling prism 42 and refractive index matching fluid 5.

[0075] Stress in the CS glass substrate 10 causes optical delay along the optical path within the body 11 of the CS glass substrate, wherein the stress is proportional to the derivative of the optical delay. The amount of optical delay can be determined from the stress-induced phase shift in the scattered light intensity distribution detected at each depth along the beam path (as LSP image 248).

[0076] Light source system

[0077] Figure 2A for Figure 1 A close-up view of the light source system 210 of the LSP system. See again. Figure 1 and Figure 2A The light source system 210, along axis A1 and downstream of the light source 212, includes a focusing lens 220, a movable light diffuser 222, and a collimating lens 224. The movable light diffuser 222 may include a holographic element configured to perform light diffusion at the LSP wavelength λ. In an example, the movable light diffuser 222 may include a rotating light diffuser or an oscillating light diffuser. One or more folding mirrors FM may optionally be used to fold the LSP system 200 to make the LSP system 200 more compact.

[0078] The light source system 210 also includes a rotatable half-wave plate 500 and a linear polarizer 600 operably arranged between the light source 212 and the focusing lens 220, wherein the rotatable half-wave plate resides upstream of the linear polarizer. When using a polarization modulator, the polarization direction of the polarizer 600 is set to match (i.e., in the same direction) the polarization direction of the polarizer 232 in the optical compensator 230 (e.g., a polarization beam splitter PBS) or more generally, the polarization direction of the optical compensator itself. The rotatable half-wave plate 500 has a front surface 502 and a rear surface 504, while the polarizer 600 has a front surface 602 and a rear surface 604. The rotatable half-wave plate 500 is operably supported by a motorized mounting bracket 510, which is configured to rotate the half-wave plate about a rotation axis AR, which in one example is parallel to axis A1 and in another example discussed below is along a tilt direction, defined by a tilt angle θ measured relative to axis A1. WP Limited. For example... Figure 2B As can be clearly seen in the front view, the rotational position of the rotatable half-wave plate is defined by an azimuth (rotation) angle φ (hereinafter, the half-wave plate angle) measured between a reference position REF in an LSP system and a position p on the half-wave plate. The half-wave plate 500 and the motorized mounting bracket constitute a half-wave plate assembly 501. In this example, the half-wave plate assembly 501 is operatively connected to and controlled by a system controller 400, and the system controller 400 can be configured to automatically control the half-wave plate assembly 501. In this example, the system controller 400 is configured to adjust the half-wave plate assembly 501 in response to the intensity of the digital image 248. In this example, the motorized mounting bracket 510 includes a high-precision motor that can rotate the half-wave plate 500 in small angular increments (e.g., less than 1 degree increments).

[0079] When using the coherent light source 212, the primary function of the light diffuser 222 is to reduce laser speckle generated by the sample under test (e.g., CS glass substrate 10 or similar CS glass articles). Speckle reduction is necessary to maintain measurement accuracy and reliability. However, the light diffuser 222 has the adverse effect of reducing light intensity (e.g., 10% to 20%), depending on the diffusion angle, the amount of birefringence induced by internal stress in the material, and the material transparency. This is generally not a problem for certain types of ceramic glass (such as glass ceramics) because only a few watts of optical power can produce sufficient scattering intensity for the exposure time t. E This is essentially less than the exposure time that might be required for non-glass ceramic samples (such as samples that do not contain crystalline phases). Unfortunately, the light diffuser 222 is also used to slightly reduce the polarization of the light 216 passing through the light diffuser 222, and this slight "depolarization" adversely affects the polarization contrast facilitated by the polarizer in the optical compensator 230.

[0080] It has been found that different CS glass types suffer from measurement accuracy problems under fixed light source intensity because the effective light intensity for one CS glass type with a certain amount of light scattering is not always effective for other CS glass types with a different amount of light scattering. For example, in some cases, one CS glass type has at least twice the amount of light scattering in an LSP system compared to another glass type. The half-wave plate 500 and polarizer 600 provide an efficient and rapid way to control the intensity of light 216 emitted by the light source 212 based on the CS glass type being measured before it is incident on the light diffuser 222. This allows for complete reduction of the scattering intensity at the digital detector 246 under cross-polarization for a given CS glass substrate 10 being measured, and generally provides increased flexibility for the LSP system 200 to measure any type of CS glass, especially when the light source 212 has relatively high power (such as a laser diode in the power range of 50 to 300 mW). Therefore, in the operation of the light source system 210, the light source 212 itself has a fixed intensity, that is, the light source 212 cannot be controlled to provide beams 216 with different output intensities.

[0081] Figure 6 A graph showing the integrated intensity I(φ) (arbitrary units, au) of the example LSP image 248 with reference to CS sample 10, without light diffuser 222 (circle) but with rotating light diffuser (square), versus the half-wave plate angle φ (degrees) of half-wave plate 500 and without polarizer 600. A 50-mW laser diode is used as the light source 212, and the digital LSP image 248 is captured by detector system 240 at various half-wave plate angles φ. The graph shows a 1.7-fold decrease in contrast with the presence of rotating light diffuser 222 compared to using half-wave plate 500 alone.

[0082] Further experiments and simulations demonstrate a preferred configuration of a rotatable half-wave plate 500 residing upstream of the polarizer 600 to control the intensity of the beam 216. In this configuration, the polarization orientation of the light source 212 does not affect the intensity range generated by the optical compensator 230, allowing the intensity of the beam 216 detached from the light source system 210 to be set to optimize the focal size on the CS substrate 10 as seen by the digital detector 246. Furthermore, the light source system 210 disclosed herein can cyclically traverse the entire range of light intensity (I1) with a 45-degree rotation of the rotatable half-wave plate 500. max to I min ).

[0083] Figure 7A and Figure 7B An LSP image 248 of an example CS glass-ceramic substrate 10 is shown, obtained using an LSP system 200 with a light source system 210 as described above but without a polarizer 600, in two orientations of a half-wave plate 500 spaced 45 degrees apart. The digital LSP image 248 was captured on the example glass-ceramic CS substrate 10 using a 50-mW laser diode as the light source 212 and a 10 ms exposure. Only using… Figure 7B The half-wave plate 500 shown cannot obtain a completely dark image because the depolarization of the light diffuser 222 and the intensity of the light 216 are too large for the positively measured CS glass substrate.

[0084] Figure 8A and Figure 8B To and Figure 7A and Figure 7B The LSP image 248 of the same CS glass-ceramic substrate 10 as described above is obtained using a light source system 210 including a half-wave plate 500 and a polarizer 600 at two orientations of the half-wave plate 500 spaced 45 degrees apart, wherein the polarizer has its polarization direction set to match the polarization direction of the polarizer 232 of the optical compensator 230. The half-wave plate angle φ is set to obtain... Figure 8B The intensity of light 216 shown reduces the intensity of digital image 248 almost completely.

[0085] One aspect of controlling the intensity (or optical power) of the light 216 before it reaches the light diffuser 222 is to provide substantially the same exposure time t for each type of measured CS glass substrate 10. E Limited exposure time t E The lower limit is the time t elapsed for a rotation of diffuser 222. R(i.e., rotation time), as explained in detail below. Here, the light diffuser 222 must be movable enough (e.g., rotate, oscillate, vibrate, translate, etc.) to make the intensity change of the light beam 216 passing through the light diffuser smooth.

[0086] For example, consider using exposure time t E The stress in the glass-ceramic CS substrate 10 is measured in 10ms. Because glass-ceramic has relatively high light scattering, this exposure time will saturate the detector and terminate the measurement; therefore, a shorter exposure time t will be required for the 50mW laser diode light source 212. E (For example, less than 1ms). But such a short exposure time t E It may not be allowed for the light diffuser 222 to operate based on the rotation time t R Sufficient movement is required. Spatial variations in the transmission of the light diffuser can cause uneven intensity variations in the beam 216, thus detrimentally affecting the accuracy of stress measurements. This inaccuracy is caused by the imaging of the diffuser rotating itself, leading to random intensity variations throughout the measurement. In the example, the exposure time t... E The rotation time t must exceed one rotation of the light diffuser 222 R In t E In the example of 10ms, for an example diffuser rotation of 10,000rpm, one rotation will take t. R = 6.02ms. Under this condition, the theoretical minimum exposure time is t. E The time is 6.02 ms, which means that condition t is met. R ≤t E Using t E =10ms, the diffuser will rotate 1.66 times per exposure.

[0087] Furthermore, the light diffuser 222 must be able to move at a sufficient speed to substantially reduce the speckle effect in the LSP image 248. The intensity of the beam 216 is adjusted using a half-wave plate 500 and a polarizer 600 to achieve the desired exposure time t. E Equal to or greater than the rotation time elapsed by the diffuser, while also providing good extinction (see...). Figure 8B This good extinction allows a wide range of CS glasses to be measured in the LSP system 200 with appropriate light contrast and speckle control, and with minimal delay and workload between measurements of different CS glass types.

[0088] Theoretically, there is no exposure time t. E The upper limit, but in reality, it requires an exposure time of t. E It is small enough to avoid the long measurement cycle time of the LSP system 200, which is necessary for its use in manufacturing processes where control is set for CS glass formation. For example, in tE With a time limit of 10ms, the total measurement cycle time is approximately 8 seconds.

[0089] In the example, a calibration step is performed to ensure that no pixel 247 in the digital detector 246 is saturated. This is based on a standard pixel brightness level of 256 values, from 0 (darkest) to 255 (brightest). In this example, the pixel intensity of 255 represents the saturation limit. It turns out that there is typically a small range of half-wave plate angles (positions) φ that prevent detector (pixel) saturation. In the example, a selected range is applied to the pixel intensity along the beam path. For example, the maximum pixel intensity cannot exceed 75% of the saturation limit of the digital detector 246, and the minimum pixel intensity cannot be less than 25% of the saturation limit. There will still be a small range of half-wave plate angles φ (i.e., positions) to choose from, but this does not affect the quality of the stress measurement results. This method is particularly useful for glass ceramics and similar highly scattering glasses, where the line image constituting the LSP image is spread out such that there is no visible “fireball” at the prism-sample interface. This is because the volumetric properties of glass ceramics cause greater scattering than typical Fresnel reflection due to a slight refractive index mismatch at the interface.

[0090] Figure 8C Similar to Figure 7A However, an example LSP image 248 of a relatively low-scattering CS glass substrate 10 is shown, in which a hot spot (bright spot) or "fireball" exists at the center of the LSP image, and the end of the cross-line image LI is the brightest. If we consider the lower left leg of the cross-line LSP image as the scattered beam of interest, we can say that there are two fireballs, one at the prism-glass interface and the other at the intersection of the glass-air interface INT. In this case, the method seeks to avoid pixel saturation along the beam path and away from the "fireball" or hot spot of the LSP image. In this case, the conditions for the half-wave plate position will be slightly different from those set for glass ceramics, but the general method for setting the half-wave plate 500 and polarizer 600 still applies.

[0091] Mitigating the adverse effects of back reflections into the light source

[0092] When the beam 216 from the light source 212 arrives at the half-wave plate 500 with normal incidence, a portion of the beam is reflected back toward the light source from both the front surface 502 and the rear surface 504 of the half-wave plate. Similarly, a portion of the beam 216, normally incident on the polarizer 600, is reflected back toward the light source 212 from both the front surface 602 and the rear surface 604 of the polarizer. When the light source 212 contains a laser, this back-reflected light can cause frequency and power fluctuations because the half-wave plate 500 and the polarizer 600 act as external cavities for the laser, causing some modes in the laser mode to share the gain medium, thus resulting in a decrease in optical power.

[0093] Figure 9 The graph shows the integrated intensity I(φ) (arbitrary unit, au) of example LSP image 248 versus the half-wave plate angle φ (degrees) of half-wave plate 500, based on data collected on example CS substrate 10 using a 50-mW laser in LSP system 200 at various half-wave plate rotation angles φ. Figure 9 The graphs show that the model predictions for contrast, which vary with the half-wave plate angle φ, have significant deviations. The dashed lines represent the ideal or expected peak and trough (maximum and minimum) intensities in the absence of back reflection. Besides the intensity fluctuations caused by back reflection, the peaks and troughs in the curves do not align with the corresponding ideal half-wave plate angles, making it difficult to accurately and repeatedly obtain appropriate intensity levels for LSP measurements across various glass types. Furthermore, the contrast pattern changes with the orientation of the light source 212, further complicating the achievement of repeatability across different LSP systems.

[0094] Figure 10 Similar to Figure 2A An embodiment of the light source system 210 is shown, wherein the rotatable half-wave plate 500 and the polarizer 600 are tilted relative to the axis A1 by a tilt angle θ, respectively. WP and θ P , such as respectively in Figure 11 and Figure 12 Clearly visible in the close-up view. The surface normals of the rotatable half-wave plate 500 and the polarizer 600 are respectively made of n HW and n p instruct.

[0095] Reference Figure 10 The light beams 216 reflected from the front surface 502 and rear surface 504 of the half-wave plate 500 (i.e., the back-reflected beams) are designated as R1 and R2, and have a reflection angle θ1 = 2θ relative to the axis A1. WP Similarly, the beams reflected from the front surface 602 and rear surface 604 of the polarizer 600 are labeled R3 and R4, and have a reflection angle θ2 = 2θ relative to the axis A1. P Tilt angle θ WP and θ P The polarizers are chosen such that the back-reflected beams R1, R2 and R3, R4 do not enter the front end of the light source 212. Since the polarizer 600 is further away from the light source 212, its tilt angle θ... P It can be less than the tilt angle θ of the half-wave plate WP An example tilt angle of θ is used in an example configuration for the light source system 210. WP =15° and θ P = 7.5°. Example angles for this type of tilt angle can range from 10° to θ.WP ≤20° and 5°≤θ P ≤10°, where the precise angle value is defined by the specific geometry of the light source system 210. In the example, the light absorber 700 can be used to intercept and absorb reflected light beams R1 to R4 before they can be reflected from a surface, such as inside a mounting conduit (not shown) used to secure various optical and mechanical components of the light source system 210.

[0096] Figure 13 The graph shows the output optical power p (mW) versus the half-wave plate angle θ (degrees) in configurations where neither the half-wave plate 500 nor the polarizer 600 is tilted (triangle, curve A), only the half-wave plate is tilted (curve B), and both the half-wave plate and the polarizer are tilted (curve C). Figure 13 As shown in the graph, the adverse effect on the output laser power of the reflected light 216 is greatest when the half-wave plate and polarizer are perpendicular to axis A1 (curve A). As used herein, "axis" generally refers to the optical axis in the direction of the beam's forward propagation, unless otherwise indicated. When the half-wave plate 500 is arranged with a tilt angle θ... WP =15° and the polarizer 600 maintains its normal orientation (i.e., θ P At θ = 0°, the output optical power P increases by approximately 50%. This is shown by curve B, where the measured absolute maximum power P remains below 10mW, indicating that back reflection from the polarizer 600 itself adversely affects the overall laser intensity / power. The polarizer 600 is then given a tilt angle θ. P =7.5°, causing the back reflections R3 and R4 to be directed away from the front end of the laser source 212. Repeated measurements of the output optical power P with both the half-wave plate 500 and the polarizer 600 operably tilted relative to axis A1 resulted in a significant jump in maximum laser intensity to approximately 20 mW, while the minimum achievable intensity remained above 5 mW, as shown in curve C. The half-wave plate also has a fast axis and a slow axis; the alignment of the fast and slow axes when the half-wave plate is tilted produces a hysteresis effect, which prevents linear polarization. In an embodiment, the half-wave plate can be designed and configured such that the rotation axis is at 45° relative to the fast and slow axes, thereby minimizing the change in hysteresis when tilted.

[0097] exist Figure 13 The inability to reach a minimum power / intensity value close to 0mW in the curve is attributed to the sensitivity of the specific quartz half-wave plate 500 used in the experiment to the angle of incidence (AOI) of the incident beam 216. According to information from the manufacturer's website, the amount of delay achieved through the quartz half-wave plate is highly dependent on the AOI, and at θ... WPA wavelength close to 0.25 is achieved at 15°. Half-wave plates 500 using less AOI-sensitive materials such as polymers provide significantly better results, as seen with... Figure 13 The same sloping configuration as curve C Figure 14 As shown. Another option is to place the polarizer 600 upstream of the half-wave plate 500, allowing for a smaller AOI at the half-wave plate. This option works when the given polarizer 600 is less sensitive to AOI than the half-wave plate 500, and switching the order of these components still provides an overall net benefit. Another option is to place the half-wave plate far enough from the light source 212 that the required tilt angle θ is achieved. WP It falls within the AOI tolerance of the half-wave plate.

[0098] Figure 15 Similar to Figure 9 However, the half-wave plate 500 and the polarizer 600 are operably tilted in the light source system 210 as described above. Figure 15 The measured modulation pattern closely matches the ideal (model) result. The orientation of the laser source 212 does not affect the range of achievable intensities and, in the example, can be set to optimize the focal spot size on the CS sample 10, as seen by the digital detector 246 in the LSP system 200.

[0099] Therefore, once the half-wave plate angle φ of the half-wave plate 500 is set to provide the optimal intensity of the beam 216 for a given stress measurement, and the polarizer orientation (polarization direction) is set to match the orientation of the polarizer 232 of the optical compensator 230, the half-wave plate 500 and the polarizer 600 can then be tilted to their respective tilt angle θ. WP and θ P The angle was chosen to reduce the adverse effects of back reflection.

[0100] For purposes of explanation, the foregoing description has been described with reference to specific embodiments. However, the above illustrative discussion is not intended to be exhaustive or to limit the invention to the precise forms disclosed. In view of the foregoing teachings, many modifications and variations are possible. Embodiments have been chosen and described to best explain the principles of the technology and its practical application. Thus, those skilled in the art can utilize various modifications according to the contemplated particular purpose to best utilize the technology and various embodiments. For the purpose of clarity and precise description, features are described herein as part of the same or separate embodiments; however, it should be understood that the scope of the invention may include embodiments having all or some of the described features.

[0101] Although the disclosure and examples have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications should be understood to be included within the scope of this disclosure and examples as defined by the claims. Ultimately, the patents mentioned in this application and the entire disclosure herein are hereby incorporated by reference.

Claims

1. A method for performing stress measurement on chemically strengthened glass using a light-scattering polarization LSP system, said light-scattering polarization LSP system having a light source system for emitting a light beam, an optical compensator, and an integration time t. I A digital detector, the method comprising: a) The intensity of the light beam is adjusted by aligning the first polarizer with the second polarizer in the optical compensator to have a matched polarization direction, using a rotatable half-wave plate and the first polarizer operably disposed between the light source and a rotating light diffuser having a rotation time t. R By rotating the rotatable half-wave plate to the exposure time t E Falling within the exposure range R t E The alignment is achieved by positioning within the space; and b) Using the aforementioned exposure time t E Perform exposure to obtain the stress measurement.

2. The method according to claim 1, characterized in that, The chemically strengthened glass includes a first chemically strengthened substrate having a first amount of light scattering, and the method further includes: The first chemically reinforced substrate in the LSP system is replaced with a second chemically reinforced substrate having a second amount of light scattering, wherein the second amount of light scattering differs from the first amount of light scattering by at least two times. Repeat operations a) and b) on the second chemically reinforced substrate.

3. The method according to claim 1 or claim 2, characterized in that, The adjustment includes measuring the contrast of the intensity distribution of the LSP image captured by the digital detector.

4. The method according to claim 1 or claim 2, characterized in that, The exposure time t E Between 5 ms and 10 ms.

5. The method according to claim 1 or claim 2, characterized in that, The light source system includes a light beam along its travel axis, wherein the rotatable half-wave plate and the polarizer form back-reflected light from the light beam, and the method further includes operable to tilt at least one of the rotatable half-wave plate and the first polarizer relative to the axis to prevent the back-reflected light from being directed to the light source.

6. The method according to claim 5, characterized in that, The back-reflected light is directed to one or more light absorbers.

7. The method according to claim 5, characterized in that, The rotatable half-wave plate has a tilt angle θ relative to the axis. WP The tilt angle θ WP In 10 ≤ θ WP ≤ 20 Within the range.

8. The method according to claim 5, characterized in that, The polarizer has a tilt angle θ relative to the axis. P The tilt angle θ P In 5 ≤ θ P ≤ 10 Within the range.

9. The method according to claim 1 or claim 2, characterized in that, The light source includes a laser diode having optical power in the range of 20 to 300 milliwatts.

10. The method according to claim 1 or claim 2, characterized in that, The rotating light diffuser includes a holographic light diffuser.

11. The method according to claim 1 or claim 2, characterized in that, The second polarizer includes a polarization beam splitter.

12. The method of claim 1 or claim 2, further comprising rotating the rotatable half-wave plate using an electrically driven mounting bracket capable of operably supporting the rotatable half-wave plate.

13. The method according to claim 12, characterized in that, The rotation of the rotatable half-wave plate is performed using a controller configured to automatically operate the motorized mounting bracket.

14. The method according to claim 1 or claim 2, characterized in that, The half-wave plate comprises a polymer material.

15. The method according to claim 1 or claim 2, further comprising: A digital LSP image of the chemically strengthened glass is formed on a digital detector having a saturation limit and comprising pixels having corresponding pixel intensities as defined by the digital LSP image; and The adjustment of the intensity of the light beam includes limiting the pixel intensity between 25% and 75% of the saturation limit.

16. An illumination system that provides light intensity control in a light-scattering polarized light propagation system (LSP) for measuring stress in chemically strengthened glass, said illumination system being coupled with an optical compensator and having an integration time t I The digital detector optical communication includes the following components arranged sequentially along the axis: A light source that emits a light beam of first intensity along the axis; Rotatable half-wave plate; A first polarizer has a first polarization direction, which is aligned with the second polarization direction of a second polarizer in the optical compensator. A rotatable light diffuser having a rotation time t R ;and The rotatable half-wave plate is set at a rotation angle such that the light beam leaving the first polarizer and incident on the rotatable light diffuser has a second intensity less than the first intensity, thus allowing the LSP system to have an exposure time t for the chemically strengthened glass. E To measure the stress in the chemically strengthened glass, the exposure time t E Falling within the exposure range R t E Inside.

17. The lighting system according to claim 16, characterized in that, The rotatable half-wave plate and the polarizer form backscattered light, and at least one of the rotatable half-wave plate and the polarizer is operably tiltable relative to the axis to guide the backscattered light to the light source.

18. The lighting system according to claim 16 or claim 17, characterized in that, The rotatable half-wave plate has a tilt angle θ relative to the axis. WP The tilt angle θ WP In 10 ≤ θ WP ≤ 20 Within the range.

19. The lighting system according to claim 16 or claim 17, characterized in that, The polarizer has a tilt angle θ relative to the axis. P The tilt angle θ P In 5 ≤ θ P ≤ 10 Within the range.

20. The lighting system according to claim 17, characterized in that, The back-reflected light is directed to one or more light absorbers.

21. The lighting system according to claim 16 or claim 17, characterized in that, The exposure time t E Between 5ms and 10ms.

22. The lighting system according to claim 16 or claim 17, characterized in that, The light source includes a laser diode having optical power in the range of 20 to 300 milliwatts.

23. The lighting system according to claim 16 or claim 17, characterized in that, The light diffuser includes a holographic light diffuser.

24. The lighting system according to claim 16 or claim 17, characterized in that, The second polarizer includes a polarization beam splitter.

25. The lighting system of claim 16 or claim 17, further comprising a rotatable motorized mounting bracket that rotatably supports the rotatable half-wave plate.

26. The lighting system of claim 25, further comprising a controller configured to automatically operate the rotatable motorized mounting bracket.

27. The lighting system according to claim 16 or claim 17, characterized in that, The half-wave plate comprises a polymer material.

28. The lighting system according to claim 16 or claim 17, further comprising: The optical compensator.

Images