Glass articles and methods for laser welding low thermal expansion glass

Abstract

A method for welding low thermal expansion glass includes applying an inorganic film on a first surface of a first glass substrate, positioning a second glass substrate with a second surface of the second glass substrate facing towards the first surface of the first glass substrate, and exposing one side of the inorganic film to a pulsed laser having a power of at least 2 W, a pulse duration of at least 0.5 ns, and a repetition rate of at least 0.2 MHz. The first glass substrate and second glass substrate each have a CTE less than or equal to about 3 ppm / °C-1. The pulsed laser heats and melts the inorganic film and heats the first glass substrate, the second glass substrate, or both to produce a glass article comprising the first glass substrate and the second glass substrate rigidly joined at a weld region.

Description

GLASS ARTICLES AND METHODS FOR LASER WELDING LOW THERMAL EXPANSION GLASSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 606,248 filed on December 5, 2023, the content of which is incorporated herein by reference in its entirety for all purposes.BACKGROUNDField

[0002] The present specification generally relates to glass articles and methods for producing glass articles, in particular, to glass articles comprising low thermal expansion glass and methods for welding low thermal expansion glass.Technical Background

[0003] Laser welding has been used in applications for joining glasses to produce complex glass structures and making hermetically-sealed packages and structures. In many cases, CO2 lasers are used to heat the glass surfaces, but CO2 lasers have limited capabilities for use in joining thick pieces of glass or when thermally sensitive packages are used. Ultrafast lasers having pulse durations of less than 10 picoseconds (ps) and high repetition rate are capable of creating absorption in the transparent materials, such as glass, due to multiphoton absorption and, therefore, are capable of generating heat at desired locations around surface of the glass object. In many cases, the focusing is done near glass interfaces to locally melt the glass to create a bond. In another approach, a thin absorbing layer can be disposed on one of the glass surfaces so the laser radiation, either continuous wave or pulsed, can create a heat source at the glass interface. These existing approaches work reasonably well with glass materials having low melting point and relatively high coefficient of thermal expansion (CTE) (i.e., CTE >3 ppm 1 / °C), because molten glass easily expands during heating and flows to create a bond between two glass pieces. The existing methods also work when the gap between two glasses does not form optical contact (i.e., optical contact being a gap < 0.1 micron), and welding with gaps up to 1 -2 microns between the glass parts has been demonstrated. However, these existing laser welding techniques are not suitable for all circumstances.SUMMARY

[0004] Accordingly, an ongoing need exists for glass articles comprising welded low thermal expansion glass and methods for welding low thermal expansion glass. According to a first aspect disclosed herein, a method for welding low thermal expansion glass may comprise applying an inorganic film on a first surface of a first glass substrate, positioning a second glass substrate with a second surface of the second glass substrate facing towards the first surface of the first glass substrate, and exposing one side of the inorganic film to a pulsed laser having a power of greater than about 2 W, a pulse duration of greater than or equal to about 0.5 ns, and a repetition rate of greater than or equal to about 0.2 MHz. The first surface and the second surface may be spaced apart by a distance of up to about 10 pm. The first glass substrate and the second glass substrate may each comprise a low thermal expansion glass having a coefficient of thermal expansion of less than or equal to about 3 ppm / oC-1(3x1 O’6°C1) in a temperature range of from -20 °C to 250 °C. Exposing the inorganic film to the pulsed laser may heat and melt the inorganic film and may heat the first glass substrate, the second glass substrate, or both to produce a glass article comprising the first glass substrate and the second glass substrate rigidly joined at a weld region.

[0005] A second aspect of the present disclosure may include the first aspect, wherein the low thermal expansion glasses of the first glass substrate and the second glass substrate may each have a coefficient of thermal expansion less than or equal to about 2xl0-6°C"1, or from about 0.05x1 O’6°C"1to about 3x1 O’6°C"1, or from about 0. 1x1 O’6°C"1to about 2x1 O’6°C"1at a temperature range of from -20 °C to 250 °C.

[0006] A third aspect of the present disclosure may include any one of the first or second aspects, wherein the low thermal expansion glass of the first glass substrate, the second glass substrate, or both may have a softening point temperature of greater than or equal to about 1300 °C, greater than or equal to about 1400 °C, greater than or equal to about 1500 °C, greater than or equal to about 1600 °C, greater than or equal to about 1700 °C, or from about 1300 °C to about 1900 °C, or from about 1700 °C to about 1900 °C.

[0007] A fourth aspect of the present disclosure may include any one of the first through third aspects, wherein the first glass substrate, the second glass substrate, or both may comprise fused silica or doped fused silica.

[0008] A fifth aspect of the present disclosure may include any one of the first through fourth aspects, wherein the first glass substrate, the second glass substrate, or both may comprise an Ultra Low Expansion (ULE) glass.

[0009] A sixth aspect of the present disclosure may include any one of the first through third aspects, wherein the first glass substrate may be fused silica or ULE glass and the second substrate may be unconsolidated silica soot or partially consolidated silica soot.

[0010] A seventh aspect of the present disclosure may include any one of the first through sixth aspects, wherein the pulsed laser may have a wavelength of from about 260 nm to about 1100 nm, from about 260 nm to about 550 nm, from about 260 nm to about 400 nm, from about 350 nm to about 1100 nm, from about 350 nm to about 550 nm, from about 350 nm to about 400, of from about 355 nm to about 532 nm.

[0011] An eighth aspect of the present disclosure may include any one of the first through seventh aspects, wherein the first glass substrate and the second glass substrate may both be transparent to the pulsed laser at a wavelength of the pulsed laser.

[0012] A ninth aspect of the present disclosure may include any one of the first through eighth aspects, wherein the power of the pulsed laser may be from about 2 W to about 50 W, such as from about 5 W to 50 W, or from about 10 W to about 50 W.

[0013] A tenth aspect of the present disclosure may include any one of the first through ninth aspects, wherein the pulsed laser may have an energy density of less than about 25 J / cm2, such as from about 0.05 J / cm2to about 25 J / cm2.

[0014] An eleventh aspect of the present disclosure may include any one of the first through tenth aspects, wherein the pulsed laser may have a pulse duration of from about 0.5 nanoseconds (ns) to about 20 ns, such as from about 1 ns to about 20 ns, from about 2 ns to about 20 ns.

[0015] A twelfth aspect of the present disclosure may include any one of the first through eleventh aspects, wherein the repetition rate of the pulsed laser may be greater than or equal to about 1 MHz, or from about 0.2 MHz to about 50 MHz, from about 0.5 MHz to about 30 MHz, or from about 1 MHz to about 10 MHz.

[0016] A thirteenth aspect of the present disclosure may include any one of the first through twelfth aspects, wherein the pulsed laser may have a spot size of from about 50 pm to about 700 pm at the point where the pulsed laser is incident on the inorganic film.

[0017] A fourteenth aspect of the present disclosure may include any one of the first through thirteenth aspects, wherein the pulsed laser may be positioned so that the inorganic fdm is disposed between a lens of a laser system that produces the pulsed laser and a focal point of the pulsed laser.

[0018] A fifteenth aspect of the present disclosure may include any one of the first through fourteenth aspects, wherein the inorganic film may comprise a metal coating comprising one or more metals that: absorb light in a wavelength of from about 260 nm to about 1200 nm or from about 260 nm to about 550 nm with an absorbance of greater than 10%; have high transmission of light when diffused into the first glass substrate, the second glass substrate, or both, where high transmission is a transmission of greater than or equal to 99%; and can be etched by HF.

[0019] A sixteenth aspect of the present disclosure may include any one of the first through fifteenth aspects, wherein the inorganic film may comprise a metal coating comprising a metal having a melting temperature less than a melting temperature of the first glass substrate and the second glass substrate, such as melting temperature of from about 400 °C to about 900 °C, such as from about 500 °C to about 600 °C.

[0020] A seventeenth aspect of the present disclosure may include any one of the first through sixteenth aspects, wherein the inorganic film may comprise a metal coating comprising a metal selected from the group consisting of stainless steel, copper, chromium, nickel, titanium, aluminum, chromiumoxynitride (CrON), iron, and alloys thereof.

[0021] An eighteenth aspect of the present disclosure may include any one of the first through seventeenth aspects, wherein the inorganic film may be a metal coating comprising, consisting of, or consisting essentially of stainless steel, copper, chromium, an alloy of chromium and chromiumoxynitride (CrON), nickel, titanium, aluminum, iron, or an alloy of nickel and aluminum.

[0022] A nineteenth aspect of the present disclosure may include any one of the first through eighteenth aspects, wherein the inorganic film may have a thickness of less than about 500 nm, less than about 200 nm, less than about 100 nm, less than about 50 nm, less than about 20 nm, or from about 10 nm to about 500 nm.

[0023] A twentieth aspect of the present disclosure may include any one of the first through nineteenth aspects, wherein applying the inorganic film may comprise sputtering or vapor deposition of a metal coating onto the first surface of the first glass substrate.

[0024] A twenty-first aspect of the present disclosure may include any one of the first through twentieth aspects, further comprising translating the pulsed laser or the first and second substrates relative to one another to produce a weld line between the first substrate and the second substrate.

[0025] A twenty-second aspect of the present disclosure may include the twenty-first aspect, comprising translating the pulsed laser or the first and second substrates relative to one another at a relative speed of from about 1 mm / s to about 50 mm / s, such as from about 1 mm / s to 20 mm / s.

[0026] A twenty-third aspect of the present disclosure may include any one of the twenty- first or twenty-second aspects, comprising repeating the translating the pulsed laser of the first and second substrates relative to one another to produce a plurality of weld lines spaced apart from one another.

[0027] A twenty-fourth aspect of the present disclosure may include any one of the twenty- first through twenty-third aspects, wherein each weld line may have a width of from about 50 pm to about 200 pm, such as from about 100 pm to about 200 pm.

[0028] A twenty-fifth aspect of the present disclosure may include any one of the first through twenty-fourth aspects, wherein the method does not required the first glass substrate and the second glass substrate to be in optical contact.

[0029] A twenty-sixth aspect of the present disclosure may include any one of the first through twenty-fifth aspects, further comprising removing residual inorganic film by etching with a metal etchant.

[0030] A twenty-seventh aspect of the present disclosure may include any one of the first through twenty-sixth aspects, and may be directed to a glass article produced by the methods in any one of the first through twenty-sixth aspects.

[0031] A twenty-eighth aspect of the present disclosure may include the twenty-seventh aspect, wherein the glass article may be transparent, such as being transparent to light in the visible spectrum.

[0032] A twenty-ninth aspect of the present disclosure may include any one of the twentyseventh through twenty-eighth aspects, wherein the glass article may comprise one or more weld lines.

[0033] A thirtieth aspect of the present disclosure may include the twenty-ninth aspect, wherein each of the weld lines may have a width of from about 50 pm to about 200 pm, such as from about 100 pm to about 200 pm.

[0034] A thirty-first aspect of the present disclosure may include any one of the twentyninth through thirtieth aspects, wherein between each of the weld lines, the first glass substrate and the second glass substrate may be separated by a distance of from about 2 pm to about 10 pm, from about 3 pm to about 10 pm, from about 5 pm to about 10 pm, or from about 2 pm to about 5 pm.

[0035] A thirty-second aspect of the present disclosure may include any one of the twentyseventh through thirty-first aspects, wherein the glass article, before annealing, may exhibit an internal stress region having a stress of greater than or equal to about 10 MPa, greater than or equal to about 20 MPa, greater than or equal to about 30 MPa, or greater than or equal to about 40 MPa.

[0036] A thirty-third aspect of the present disclosure may include the thirty-second aspect, wherein the stress region may be asymmetric relative to the interface between the first glass substrate and the second glass substrate.

[0037] A thirty-fourth aspect of the present disclosure may include the thirty-third aspect, wherein at least 90 % of the stress region may be disposed in the first glass substrate or the second glass substrate.

[0038] A thirty-fifth aspect of the present disclosure may include any one of the twentyseventh through thirty-fourth aspects, wherein the first glass substrate and the second glass substrate may comprise metal particles or metal oxides from the inorganic film diffused into the first glass substrate and the second glass substrate.

[0039] A thirty-sixth aspect of the present disclosure may include any one of the twentyseventh through thirty-fifth aspects, wherein the weld region may have a composition different from a bulk composition of the first glass substrate, the second glass substrate, or both.

[0040] A thirty-seventh aspect of the present disclosure may include the thirty-sixth aspect, wherein the composition of the weld region may comprise metal particles, metal oxides, or both from the inorganic film diffused into the first glass substrate, the second glass substrate, or both, wherein the metal particles, metal oxides, or both in the weld region are not present in the bulk composition of the first glass substrate, the second glass substrate, or both.

[0041] A thirty-eighth aspect of the present disclosure may include any one of the twentyseventh through thirty-seventh aspects, wherein a stress region of the weld region may have a ratio of depth to width of from 2 to 10, wherein the ratio of depth to width is the depth of the stress in the stress region divided by the width of the stress in the stress region, the depth of the stress in the stress region is a distance between a depth of the stress into the first glass substrate and the depth of the stress into the second glass substrate, and the width of the stress in the stress region is the width of the stress in a direction perpendicular to a direction of a weld line.

[0042] A thirty-ninth aspect of the present disclosure may include any one of the twentyseventh through thirty-eighth aspects, wherein the glass article may be a glass fiber preform.

[0043] A fortieth aspect of the present disclosure may include any one of the twentyseventh through thirty-eighth aspects, wherein the glass article may be an optical component, such as a mirror, lens, or other optical structure.

[0044] A forty-first aspect of the present disclosure may include a glass article that may comprise a first glass substrate and a second glass substrate rigidly coupled to each other by at least one weld region. The first glass substrate and the second glass substrate may each have a coefficient of thermal expansion of less than or equal to about 3 ppm / oC-1(3x1 O’6°C1) in a temperature range of from -20 °C to 250 °C. The first glass substrate and the second glass substrate may comprise metal particles or metal oxides diffused into the first glass substrate and the second glass substrate. The metal particles or metal oxides may comprise a metal selected from the group consisting of stainless steel, copper, chromium, chromiumoxynitride, aluminum, nickel, titanium, iron, and combinations thereof.

[0045] A forty-second aspect of the present disclosure may include the forty-first aspect, wherein the glass article may be transparent.

[0046] A forty-third aspect of the present disclosure may include any one of the forty-first through forty-second aspects, wherein the glass article may comprise one or more weld lines.

[0047] A forty-fourth aspect of the present disclosure may include the forty-third aspect, wherein each of the weld lines may have a width of from about 50 pm to about 200 pm, such as from about 100 pm to about 200 pm.

[0048] A forty-fifth aspect of the present disclosure may include any one of the forty-third through forty-fourth aspects, wherein between each of the weld lines, the first glass substrateand the second glass substrate may be separated by a distance of from about 2 pm to about 10 pm, or from about 5 pm to about 10 pm.

[0049] A forty-sixth aspect of the present disclosure may include any one of the forty-first through forty-fifth aspects, wherein the glass article, before annealing, may exhibit an internal stress region having a stress of greater than or equal to about 10 MPa, greater than or equal to about 20 MPa, greater than or equal to about 30 MPa, or greater than or equal to about 40 MPa.

[0050] A forty-seventh aspect of the present disclosure may include the forty-sixth aspect, wherein the stress region may be asymmetric relative to the interface between the first glass substrate and the second glass substrate.

[0051] A forty-eighth aspect of the present disclosure may include the forty-seventh aspect, wherein at least 90 % of the stress region may be disposed in the first glass substrate or the second glass substrate.

[0052] A forty-ninth aspect of the present disclosure may include any one of the forty-first through forty-eighth aspects, wherein the metal particles or oxides may be diffused into the first glass substrate, the second glass substrate, or both to a depth of less than or equal to about 1 pm from the interface between the first glass substrate and the second glass substrate.

[0053] A fiftieth aspect of the present disclosure may include any one of the forty-first through forty-ninth aspects, wherein a stress region of the weld region may have a ratio of depth to width of from 2 to 10, wherein the ratio of depth to width is the depth of the stress in the stress region divided by the width of the stress in the stress region, the depth of the stress in the stress region is a distance between a depth of the stress into the first glass substrate and the depth of the stress into the second glass substrate, and the width of the stress in the stress region is the width of the stress in a direction perpendicular to a direction of a weld line.

[0054] A fifty-first aspect of the present disclosure may include any one of the forty-first through fiftieth aspects, wherein the glass article may be a glass fiber preform.

[0055] A fifty-second aspect of the present disclosure may include any one of the forty- first through fiftieth aspects, wherein the glass article may be an optical component.

[0056] A fifty-third aspect of the present disclosure may include a method for welding low thermal expansion glass, the method comprising providing a first glass substrate comprising an ultra-low expansion glass (ULE glass); providing a second glass substrate comprising a ULE glass or fused silica; positioning the second glass substrate with a second surface of the secondglass substrate facing towards a first surface of the first glass substrate; and exposing an interface between the first glass substrate and the second glass substrate to a pulsed laser having a wavelength of from about 260 nm to about 400 nm, a power of greater than about 2 W, a pulse duration of greater than or equal to about 0.5 ns, and a repetition rate of greater than or equal to about 0.2 MHz. The first surface and the second surface may be spaced apart by a distance of up to about 10 pm. The first glass substrate and the second glass substrate may each have a coefficient of thermal expansion of less than or equal to about 3 ppm / oC-1(3x1 O’6°C1) in a temperature range of from -20 °C to 250 °C. The exposing to the pulsed laser may heat the first glass substrate, the second glass substrate, or both to produce a glass article comprising the first glass substrate and the second glass substrate rigidly joined at a weld region.

[0057] Additional features and advantages of the systems and methods disclosed herein will be set forth in the detailed description, which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description, which follows, the claims, as well as the appended drawings.

[0058] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG. 1 schematically depicts an end cross-sectional view of a glass article, according to one or more embodiments shown and described herein;

[0060] FIG. 2 schematically depicts a top cross sectional view of the glass article of FIG. 1 taken at reference line 2-2 in FIG. I, according to one or more embodiments shown and described herein;

[0061] FIG. 3 schematically depicts an end cross-sectional view of a weld stack prior to welding; according to one or more embodiments shown and described herein;

[0062] FIG. 4 schematically depicts an end cross-sectional view of the weld stack of FIG. 3 during welding, according to one or more embodiments shown and described herein;

[0063] FIG. 5 schematically depicts a side cross-sectional view of the weld stack of FIG. 3 during welding, according to one or more embodiments shown and described herein;

[0064] FIG. 6 schematically depicts a "razor blade test" for measuring surface energy bond strength, according to one or more embodiments shown and described herein;

[0065] FIG. 7 graphically depicts black body radiation (y-axis) determined by spectrometry as a function of wavelength (x-axis) at 4200 °C, according to one or more embodiments shown and described herein;

[0066] FIG. 8 is a photographic image of a welded glass article comprising the first glass substrate and the second glass substrate, both of which are fused silica, joined by a plurality of welds, where the image is taken with polarized light to reflect birefringence in the glass produced by the disclosed process, according to embodiments shown and described herein;

[0067] FIG. 9 graphically depicts a birefringence field around weld regions in a welded glass article, according to embodiments shown and described herein;

[0068] FIG. 10 graphically depicts stress in the glass (y-axis) as a function of position in the glass (x-axis) for the welded glass article of FIG. 11, where the positions are shown in FIG. 9, according to embodiments shown and described herein;

[0069] FIG. 11 is a photographic image of a welded glass article comprising the first glass substrate and the second glass substrate, both of which are fused silica, joined by a plurality of welds that are spaced close together, where the image is taken with polarized light to reflect birefringence in the glass produced by the disclosed process, according to embodiments shown and described herein;

[0070] FIG. 12 is a photographic image of a welded glass article comprising the first glass substrate and the second glass substrate, both of which are fused silica, joined by a weld accomplished with copper as the inorganic film, where the image is taken with polarized light to reflect birefringence in the glass produced by the disclosed process, according to embodiments shown and described herein;

[0071] FIG. 13 is a photographic image of a weld line of a welded glass article formed of a first glass substrate comprising fused silica and a second substrate comprising partially consolidated silica soot, according to embodiments shown and described herein;

[0072] FIG. 14 is a photographic image of weld lines of a welded glass article formed by welding a first glass substrate comprising fused silica and a second glass substrate comprising ULE glass, according to embodiments shown and described herein;

[0073] FIG. 15 is a photographic image of a welded glass article comprising the first glass substrate (fused silica) and the second glass substrate (ULE glass) joined by a weld, where the image is taken with polarized light to reflect birefringence in the glass produced by the disclosed process, according to embodiments shown and described herein; and

[0074] FIG. 16 is a photograph of the welded glass article of FIG. 15 taken without polarized light to show the birefringence, so no stress is pattern is visible, according to embodiments shown and described herein.

[0075] The drawings accompanying this application are not to scale and certain features in the drawings may be exaggerated for purposes of illustration.DESCRIPTION

[0076] Reference will now be made in detail to embodiments of the glass articles and methods of producing glass articles of the present disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. Referring now to FIG. I, one embodiment of a glass article 100 disclosed herein is schematically depicted. The glass articles 100 disclosed herein may include a first glass substrate 110 and a second glass substrate 120 rigidly coupled to each other by at least one weld region 160. The first glass substrate 110 and the second glass substrate 120 each have a coefficient of thermal expansion of less than or equal to about 3 ppm / oC-1(3xl0-6°C"1) in a temperature range of from -20 °C to 250 °C. The first glass substrate 110 and the second glass substrate 120 may each comprise metal particles or metal oxides diffused into the first glass substrate 110 and the second glass substrate 120. The metal particles or metal oxides may comprise a metal selected from the group consisting of stainless steel, copper, chromium, chromiumoxynitride, aluminum, nickel, titanium, iron, and combinations thereof.

[0077] Referring to FIGS. 3-5, methods for welding low thermal expansion glass to produce the welded glass article 100 may include applying an inorganic film 130 on a first surface 112 of the first glass substrate 110 and positioning the second glass substrate 120 with a second surface 122 of the second glass substrate 120 facing towards the first surface 112 ofthe first glass substrate 110. The first surface 112 and the second surface 122 may be spaced apart by a distance of up to about 10 pm. The first glass substrate 110 and the second glass substrate 120 may each comprise a low thermal expansion glass having a coefficient of thermal expansion of less than or equal to about 3 ppm / oC-1(3x1 O’6°C1) in a temperature range of from -20 °C to 250 °C. The methods may further include exposing one side of the inorganic film 130 to a pulsed laser 150 having a power of greater than about 2 W, where the pulsed laser 150 may be a pulsed laser having a pulse duration of greater than or equal to about 0.5 nanoseconds (ns) and a repetition rate of greater than or equal to about 0.2 megahertz (MHz), wherein exposing the inorganic film to the pulsed laser 150 heats and melts the inorganic film 130 to produce a plasma and heats the first glass substrate 110, the second glass substrate 120, or both to produce the glass article 100 comprising the first glass substrate 110 and the second glass substrate 120 rigidly joined at a weld region 160.

[0078] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that specific orientations be required with any apparatus. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification.

[0079] Directional terms as used herein - for example up, down, right, left, front, back, top, bottom - are made only with reference to the figures as drawn and the coordinate axis provided therewith and are not intended to imply absolute orientation.

[0080] As used herein, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise.

[0081] Where a range of numerical values is recited herein, comprising upper and lower values, unless otherwise stated in specific circumstances, the range is intended to include theendpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the disclosure be limited to the specific values recited when defining a range. Further, when an amount, concentration, or other value or parameter is given as a range, one or more preferred ranges or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether such pairs are separately disclosed. Finally, when the term "about" is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to.

[0082] As used herein, the term "about" means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is "about" or "approximate" whether or not expressly stated to be such. In embodiments, the term "about" may represent variation around the recited value of + / -3% of the recited value.

[0083] As used herein, the "beam waist" of a laser beam refers to the point along the beam path of the laser beam at which point the power density of the laser beam is greatest.

[0084] As used herein, the terms "upstream" and "downstream" refer to the positions of processing stations and other components of the converter relative to a direction of travel of the glass tube through the converting process. For instance, a first processing station is "upstream" of a second processing station if the glass tube encounters the first processing station before encountering the second processing station. Conversely, the first processing station is "downstream" of the second processing station if the glass tube encounters the second processing station before encountering the first processing station.

[0085] As used herein, the terms "upbeam" and "downbeam" refer to the positioning of two or more features of a system relative to the direction of travel of a laser beam along a beam pathway through the system. A first component may be considered to be upbeam of a second component if the laser beam encounters the first component before encountering the second component. Conversely, a first component may be considered to be downbeam of a second component when the laser beam encounters the second component before encountering the first component.

[0086] As used herein, the term "optical contact" refers to a separation between glass parts of less than the wavelength of UV light used to weld the glass substrates, such as a gap of less than or equal to 0.1 micrometer (micron).

[0087] Laser welding has been used in applications for joining glasses to produce complex glass structures and making hermetically-sealed packages and structures. In many cases, CO2 lasers are used to heat the glass surfaces, but CO2 lasers have limited capabilities for use in joining thick pieces of glass or when thermally sensitive packages are used. Ultrafast lasers having pulse durations of less than 10 picoseconds (ps) and high repetition rate are capable of creating absorption in the transparent materials, such as glass, due to multiphoton absorption and, therefore, are capable of generating heat at desired locations around surface of the glass object. In many cases, the focusing is done near glass interfaces to locally melt the glass to create a bond. In another approach, a thin absorbing layer can be disposed on one of the glass surfaces so the laser radiation, either continuous wave or pulsed, can create a heat source at the glass interface. These existing approaches work reasonably well with glass materials having low melting point and relatively high coefficient of thermal expansion (CTE) (i.e., CTE >3 ppm 1 / °C), because molten glass during heating expands and flows to create a bond between two glass pieces. These existing laser welding techniques also work when the gap between the two glass pieces does not form optical contact (gap < 0.1 micron) or for gaps up to about 1-2 microns.

[0088] However, laser welding glasses having low CTE (e.g., CTE less than about 3 ppm / °C), such as but not limited to fused silica or ultra-low expansion glass (ULE glass), is much more difficult and requires very tight optical contact between two glasses due to the low thermal expansion and inability of the glass in the molten state to close the gap between two glass pieces. Therefore, these low CTE glasses have only been able to be laser welded using lasers with ultrashort pulse durations with very tight optical contact between the glass pieces (i.e., gap between the glass pieces of less than 0.1 pm). For larger glass substrates, forming tight optical contact is very difficult and requires super flat polishing. In addition, ultrashort pulse welding provides relatively narrow weld lines (e.g., weld widths of from ~ 10-20 pm per pass), which requires multiple weld lines between the glass pieces to ensure strong bond. Welding glass with ultrashort ultrafast lasers typically are configured so that the interface between the two glass substrates is between the focal point of the laser beam and the laser source. In this configuration, the volume of glass effected by the laser is limited due to the two- photon process. Therefore, for existing ultrafast laser welding techniques, the resulting widthof the weld line is limited to 10-20 microns, and the ability of closing gap for hard to melt glasses with low CTE is difficult.

[0089] The present disclosure is directed to new methods for laser welding glass substrates with low CTE and / or high softening temperature and glass articles produced from laser welding the glass substrates with low CTE and / or high softening temperature. In particular, the present disclosure is directed to new methods of laser welding glass substrates with low CTE and / or high softening temperature, such as but not limited to glass substrates comprising fused silica and UKE glass, using a modified laser welding method that utilizes a pulsed laser having a longer pulse duration of a few nanoseconds (larger pulse duration pulsed lasers being significantly more cost effective compared to pulsed lasers having pulse durations in the picosecond range) and a thin inorganic film (e.g., a metal film of about 10 nm to about 500 nm thickness) disposed on the surface of one of the glass substrates.

[0090] Specifically, the methods may include depositing the inorganic film on the surface of one of the glass substrates to be joined and then assembling the two glass substrates into a weld stack, in which the surface having the inorganic film is disposed between the two glass substrates. The weld stack may then be exposed to a pulsed laser having a pulse duration of a few nanoseconds and high repetition rate (further described herein). The pulsed laser is incident on the inorganic film, which absorbs the energy from the laser, melts, and generates heat at the interface between the glass substrates. The pulsed laser with longer pulse duration in combination with the inorganic film forms a very strong plasma area at the interface between the glass substrates and avoids ablation of the glass, which is typical of longer laser pulses. The plasma area increases the temperature of the glass near the interface, which increases the absorption of the glass for absorbing the laser light, leading to further heating of a larger volume of the glass substrates proximate to the weld region. The plasma area in combination with the greater volume of glass heated using these methods causes the glass substrates to thermally expand enough to close a gap of up to 10 pm at the interface and form a bond between the two glass substrates at the weld region.

[0091] The difference from previous approach is the use of a pulsed laser with longer pulse duration of a few nanoseconds, which is longer than the ultra-short laser pulses of a few picoseconds used in existing methods. The longer pulse duration, power, and high repetition rate of the pulsed laser results in the formation the plasma area at the interface and avoiding ablation typical for long laser pulses at high power.

[0092] Use of high repetition pulsed lasers with high power produces unique conditions for welding. While these lasers can be advantageous for relatively low melting temperature glasses (e.g., softening temperature < 800 °C) and high CTE glasses (i.e., CTE > 10 ppm), the high repetition rate and high power are particularly well-suited for glass substrates having low CTE and / or high melting temperature (i.e., fused silica, ULE glass, etc). For glass substrates having low CTE (e.g., <3 ppm / °C), it is very difficult to close the gap at the interface between two glass substrates in the weld stack if the glass substrates are not in close optical contact. The methods of the present disclosure utilize pulsed lasers with high power (e.g., greater than or equal to about 2 W), long pulse duration of a few nanoseconds (e.g., from about 0.5 ns to about 20 ns), and high repetition rate (e.g., greater than about 0.2 MHz) to overcome these problem and enable formation of consistent welds even with gaps between the glass substrates of from about 2 pm to about 10 pm. In particular, the pulsed lasers with high power longer pulse duration, and high repetition rate heat a larger volume of the low CTE glass at the weld region, thereby providing enough thermal expansion to close the gap between the glass substrates.

[0093] For existing laser welding methods, the laser heats and effects a laser interaction zone that extends into the surface of the glass to a depth of less than about 20 microns. Because of low thermal expansion of the low CTE glasses and small laser interaction zone, the ability of existing laser welding methods to close a gap between substrates greater than 1 pm is limited. With the methods disclosed herein using a pulsed laser with high power, long pulse duration of greater than 0.5 ns, and high repetition rate of greater than about 2 MHz, the laser interaction zone is increased to a depth of 200 pm or greater into the glass substrate (e.g., roughly 10 times greater than existing laser welding techniques), resulting in a greater volume of glass being heated. The greater volume of glass being heated produces a greater cumulative expansion of the glass, enabling the glass to swell to close gaps of greater than about 2 pm, such as from about 2 pm to about 10 pm.

[0094] The methods disclosed herein enable welding of hard glasses having low CTE, such as fused silica and ULE. The methods can be used to weld ULE glass to fused silica and fused silica to unconsolidated silica soot or partially consolidated silica soot. The welding can be performed without forming optical contact and without highly polishing the glass substrates to achieve optical contact. The methods disclosed herein produce stable welds and welded glass articles that are transparent and clear. The methods disclosed herein also enable welding of thicker glass substrates without needing to apply pressure to the glass substrates to help close the gap between the substrates. The pulsed lasers used in the methods disclosed herein are alsomore cost effective compared to ultrafast lasers used in existing laser welding methods, among other features.

[0095] The methods of the present disclosure will not be described in further detail with reference to FIGS. 1-5. Referring now to FIGS. 3-5, the methods disclosed herein for welding low thermal expansion glass may include providing the first glass substrate 110 and the second glass substrate 120, applying the inorganic fdm 130 to a first surface 112 of the first glass substrate 110, and positioning the second glass substrate 120 with a second surface 122 of the second glass substrate 120 facing towards the first surface 112 of the first glass substrate 110. The first surface 112 and the second surface 122 may be spaced apart by a distance of up to about 10 pm. The first glass substrate 110 and the second glass substrate 120 each comprise a low thermal expansion glass having a coefficient of thermal expansion of less than or equal to about 3 ppm / oC-1(3x1 O’6°C1) in a temperature range of from -20 °C to 250 °C. Referring to FIGS. 2-3, the methods may further include exposing one side of the inorganic film 130 to an ultraviolet (UV) laser 150, which may have a power of greater than about 2 W. The pulsed laser 150 may have a repetition rate of greater than or equal to about 0.2 MHz, and a pulse duration of from 0.5 nanoseconds (ns) to about 20 ns. Exposing the inorganic film 130 to the pulsed laser 150 heats and melts the inorganic film 130 and heats the first glass substrate 110, the second glass substrate 120, or both to produce the glass article 100 comprising the first glass substrate 110 and the second glass substrate 120 rigidly joined at a weld region 160. The pulsed laser 150, the weld stack 140 comprising the first substrate 110 and second substrate 120, or both may be translated relative to the other to form a weld line.

[0096] Referring to FIG. 3, the methods disclosed herein may include providing the first glass substrate 110 and the second glass substrate 120. The first glass substrate 110 and the second glass substrate 120 may each comprise a glass having a low CTE, a high softening temperature, or both. In embodiments, the first glass substrate 110 and the second glass substrate 120 may each comprise a low CTE glass having a coefficient of thermal expansion (CTE) of less than or equal to about 5 ppm / °C (i.e., 5xl0"6°C"1), such as less than or equal to about 3xl0"6°C1, or less than or equal to about 2xl0"6°C1, where the CTE is for a temperature range of from -20 °C to 25- °C. In embodiments, the first glass substrate 110 and the second glass substrate 120 may each comprise a low CTE glass having a CTE of from about 0.05x10"6°C"1to about 5x10"6°C"1, from about 0.05x10"6°C"1to about 3x10"6°C"1, or from about 0.1x10"6°C"1to about 2x10"6°C"1at a temperature range of from -20 °C to 250 °C.

[0097] In embodiments, the first glass substrate 110 and the second glass substrate 120 may each comprise a glass having a high softening temperature. In embodiments, the first glass substrate 110 and the second glass substrate 120 may each comprise a glass having a softening temperature of greater than or equal to about 1300 °C, greater than or equal to about 1500 °C, greater than or equal to about 1600 °C, or greater than or equal to about 1700 °C. In embodiments, the first glass substrate 110 and the second glass substrate 120 may each comprise a glass having a softening temperature of from about 1300 °C to about 1900 °C, from about 1300 °C to about 1800 °C, from about 1500 °C to about 1900 °C, from about 1500 °C to about 1800 °C, from about 1600 °C to about 1900 °C, from about 1600 °C to about 1800 °C, from about 1700 °C to about 1900 °C, or from about 1800 °C to about 1900 °C. In embodiments, the first glass substrate 110 and the second glass substrate 120 may be transparent to the pulsed laser at the wavelength of the pulsed laser, such as at a wavelength of from about 260 nm to about 1100 nm, or from about 260 nm to about 550 nm.

[0098] The first glass substrate 110 and / or the second glass substrate 120 may comprise fused silica, doped fused silica, ULE glass, unconsolidated silica soot, or partially consolidated silica soot. Doped fused silica may include fused silica doped with one or more compounds other than silica, such as but not limited to titania (TiCh). In embodiments, the first glass substrate 110, the second glass substrate 120, or both may comprise fused silica or doped fused silica. In embodiments, the first glass substrate 1 10, the second glass substrate 120, or both may comprise an Ultra-Low Expansion (ULE) glass, such as but not limited to ULE® glass available from Coming Incorporated. In embodiments, the first glass substrate 110 may be fused silica or ULE glass and the second glass substrate 120 may be unconsolidated silica soot or partially consolidated silica soot. Unconsolidated silica soot may be characterized by a density of from about 0.6 to about 1.0 g / cm3. A partially consolidated silica soot may refer to a mass of silica soot that has undergone at least some degree of consolidation such that the density of the partially consolidated silica soot is greater than about 1.2 g / cm3, but is not fully consolidated to produce fused silica.

[0099] The first glass substrate 110, the second glass substrate 120, or both may have a thickness sufficient to prevent contact across the gap between the first glass substrate 112 and the second glass substrate 120 to be closed by applying pressure to bend the glass to bridge the gap. In embodiments, the first glass substrate 110, the second glass substrate 120, or both may have a thickness of up to about 20 mm, such as from about 0.5 mm to about 20 mm, from about 1 mm to about 20 mm, or from about 2 mm to about 20 mm. In embodiments, the methodsdisclosed herein do not include applying an external force or pressure to the first glass substrate 110 and the second glass substrate 120 during the welding.

[0100] Referring again to FIG. 3, the first surface 112 of the first glass substrate 110 and the second surface 122 of the second glass substrate 120 may each have a surface roughness Ra of from greater than or equal to about 10 nm, such as from about 10 nm to about 100 nm. As previously discussed, the methods disclosed herein can enable gaps of up to 10 pm between the first glass substrate 110 and the second glass substrate 120 to be closed. Thus, in embodiments, the methods disclosed herein do not include highly polishing the first surface 112 and the second surface 122 to reduce the gap to less than 2 pm. In embodiments, the first surface 112, the second surface 122, or both may be polished to the extent that the gap between the first surface 112 of the first glass substrate 110, and the second surface 122 of the second glass substrate 120 is less than or equal to 10 pm, such as from 2 pm to 10 pm.

[0101] The first surface 112 and the second surface 122 may have any desired shape, such as flat, curved, angled, etc., as long as a contour of the second surface 122 of the second glass substrate 120 is complementary to a contour of the first surface 112 of the first glass substrate 110 at the weld region 160 (FIG. 4). Referring to FIG. 3, in embodiments, the first surface 112 and the second surface 122 may be flat. In embodiments, the first surface 112 and the second surface 122 may be curved, such as when the first glass substrate 110 and the second glass substrate 120 are optical components. Although shown as flat surfaces in FIGS. 3-5, it is understood that other shapes of the first surface 112 and second surface 122 are contemplated with similar expectations of success in forming consistent welds with the methods disclosed herein.

[0102] Referring again to FIG. 3, the methods disclosed herein may include applying the inorganic film 130 on the first surface 112 of the first glass substrate 110. The inorganic film 130 may comprise a metal coating comprising one or more metals that have the following properties: (1) absorb light in a wavelength of from about 260 nm to about 1200 nm or from about 260 nm to about 550 nm, wherein the ability to absorb light in the wavelength ranges is characterized by an absorbance of greater than 10% for those wavelengths: (2) have high transmission of light when metal particles and / or metal oxides comprising the metals are diffused into the first glass substrate 110, the second glass substrate 120, or both, where high transmission is a transmission of greater than or equal to 99%; and (3) can be etched away by HF to remove any excess metal coating from non-welded regions of the interface.

[0103] In embodiments, the inorganic film 130 may comprise a metal coating comprising a metal having a melting temperature less than a softening temperature of the first glass substrate 110 and the second glass substrate 120. In embodiments, the inorganic film 130 may comprise a metal coating having a melting temperature of from about 400 °C to about 900 °C, such as from 400 °C to about 800 °C, from about 400 °C to about 700 °C, from about 400 °C to about 600 °C, from about 500 °C to about 900 °C, from about 500 °C to about 800 °C, from about 500 °C to about 700 °C, or from about 500 °C to about 600 °C.

[0104] In embodiments, the inorganic film 130 may comprise a metal coating comprising a metal selected from the group consisting of stainless steel, copper, chromium, nickel, titanium, aluminum, chromiumoxynitride (CrON), iron, and alloys thereof. In embodiments, the inorganic film 130 may be a metal coating comprising, consisting of, or consisting essentially of stainless steel, copper, chromium, an alloy of chromium and chromiumoxynitride (CrON), nickel, titanium, aluminum, iron, or an alloy of nickel and aluminum. In embodiments, the inorganic film 130 may be a metal coating comprising, consisting of, or consisting essentially of stainless steel. In embodiments, the inorganic film 130 may be a metal coating comprising, consisting of, or consisting essentially of copper.

[0105] The inorganic film 130 may be applied to the first surface 112 of the first glass substrate 110 through known deposition processes, such as but not limited to sputtering or vapor deposition. The inorganic film 130 may have a thickness tp sufficient to provide sufficient initial head during welding to form the plasma area at the weld region 160, but not so thick that the inorganic film remains as a distinguishable layer in the weld region 160. In embodiments, the inorganic film 130 may have a thickness tp of less than or equal to about 500 nm, less than or equal to about 200 nm, less than or equal to about 100 nm, less than or equal to about 50 nm, or less than or equal to about 20 nm. In embodiments, the inorganic film 130 may have a thickness tp of about 10 nm to about 500 nm, from about 10 nm to about 200 nm, from about 10 nm to about 100 nm, from about 10 nm to about 50 nm, from about 10 nm to about 20 nm, from about 20 nm to about 500 nm, from about 20 nm to about 200 nm, from about 20 nm to about 100 nm, from about 20 nm to about 50 nm, from about 50 nm to about 500 nm, from about 50 nm to about 200 nm, from about 50 nm to about 100 nm, or from about 100 nm to about 500 nm.

[0106] In embodiments, the methods may not include applying the inorganic film 130 to the first glass substrate 110 or the second glass substrate 120. For instance, when the first glasssubstrate 110 is fused silica and the second glass substrate 120 is ULE glass, the first glass substrate 110 and the second glass substrate 120 can be welded together without the inorganic film using a pulsed laser with wavelength of about 355 nm due to the greater absorption by the ULE glass of the second glass substrate 120 at a wavelength of 355 nm.

[0107] Referring again to FIG. 3, the first glass substrate 110 having the inorganic film 130 deposited on the first surface 112 and the second glass substrate 120 may be assembled in a weld stack 140. In embodiments, the methods may include positioning the second glass substrate 120 with a second surface 122 of the second glass substrate 120 facing towards the first surface 112 of the first glass substrate 110, to form the weld stack 140. In embodiments, the second glass substrate 120 may be positioned with the second surface 122 facing towards the inorganic film 130 deposited on the first surface 112 of the first glass substrate 110.

[0108] The weld stack 140 may have a gap G disposed between the second surface 112 of the second glass substrate 120 and the inorganic film 130 deposited on the first surface 112 of the first glass substrate 110. The gap G may be the result of surface roughness of the first surface 112 and the second surface 122. In embodiments, the gap G may have an average distance between the first surface 112 and the second surface 122 of from about 2 pm to about 10 pm, such as from about 2 pm to about 9 pm, from about 2 pm to about 8 pm, from about 2 pm to about 7 pm, from about 2 pm to about 6 pm, from about 2 pm to about 5 pm, from about 3 pm to about 10 pm, from about 3 pm to about 9 pm, from about 3 pm to about 8 pm, from about 3 pm to about 7 pm, from about 3 pm to about 6 pm, from about 3 pm to about 5 pm, or from about 5 pm to about 10 pm.

[0109] Referring now to FIG. 4, the methods disclosed herein include exposing the weld stack 140 to a pulsed laser 150. In particular, the methods disclosed herein include exposing one side of the inorganic film 130 to the pulsed laser 150, which may have a high power of greater than about 2 W, a high repetition rate of greater than or equal to about 0.2 MHz, and a pulse duration of greater than or equal to about 0.5 nanoseconds. Exposure to the pulsed laser 150 may cause the inorganic film to melt and form a plasma at the weld region 160 between the first glass substrate 110 and the second glass substrate 120. The heat may increase the absorption rate in the first glass substrate 110, the second glass substrate 120, or both, which may cause heating of a greater volume of the glass in the first glass substrate 110 and / or the second glass substrate 120. Heating the greater volume of glass may cause sufficient expansion of the glass to close the gap G between the first glass substrate 110 and the second glasssubstrate 120, thereby causing bonding between the first glass substrate 110 and the second glass substrate 120 at the weld region 160.

[0110] The pulsed laser 150 may have a wavelength of light that is in the absorption range of the glass composition of the first glass substrate 110, the second glass substrate 120, or both. In embodiments, the pulsed laser 150 may have a wavelength in a range of from about 260 nm to about 1100 nm, such as from about 260 nm to about 900 nm, from about 260 nm to about 550, from about 260 nm to about 532 nm, from about 300 nm to about 1100 nm, from about 300 nm to about 900 nm, from about 300 nm to about 550 nm, from about 300 nm to about 532 nm, from about 355 nm to about 1100 nm, from about 355 nm to about 900 nm, from about 355 nm to about 550 nm, of from about 355 nm to about 532 nm. In embodiments, the pulsed laser 150 may be a UV laser having a wavelength of from about 260 nm to about 400 nm. In embodiments, the pulsed laser 150 may have a wavelength of about 355 nm, such as when the inorganic film 130 contains materials, such as but not limited to stainless steel, that absorb light having wavelength of about 355 nm. In embodiments, the pulsed laser 150 may have a wavelength of about 532, such as when the inorganic film 130 contains materials, such as but not limited to copper, that have greater absorbance of light having wavelength of about 532 nm. The wavelength of the pulsed laser 150 may be selected based on the available laser wavelengths as well as the absorption of the materials used for the inorganic film 130 and / or the materials for the glass substrates.

[0111] The pulsed laser 150 may have a power sufficient to heat and melt the inorganic film 130 and heat the glass of the first glass substrate 110 and / or second glass substrate 120 at the repetition rate and pulse duration. In embodiments, the pulsed laser 150 may have a power of greater than or equal to about 2 Watts (W), greater than or equal to about 5 W, or even greater than or equal to about 10 W. In embodiments, the pulsed laser 150 may have a power of from about 2 W to about 50 W, from about 5 W to about 50 W, or even from about 10 W to about 50 W.

[0112] The pulsed laser 150 may have an energy density that is less than a laser ablation threshold for the glass substrates. For a pulsed laser 150 having a pulse duration of from about 0.2 ns to about 20 ns, as disclosed herein, the threshold energy density at which laser ablation of the glass occurs is a range of from about 100 Joules per square centimetre (J / cm2) to about 1000 J / cm2. To avoid laser ablation, the pulsed laser 150 may have an energy density below this range. In embodiments, the pulsed laser 150 may have an energy density of less than orequal to about 25 J / cm2, such as less than or equal to about 15 J / cm2, less than or equal to about 10 J / cm2, less than or equal to about 5 J / cm2, or less than or equal to about 1 J / cm2, where the energy density is at the point where the pulsed laser 150 is incident on the inorganic film 130. In embodiments, the pulsed laser 150 may have an energy density of from about 0.05 J / cm2to about 25 J / cm2, from about 0.05 J / cm2to about 15 J / cm2, from about 0.05 J / cm2to about 10 J / cm2, from about 0.05 J / cm2to about 5 J / cm2, or from about 0.05 J / cm2to about 1 J / cm2at the point where the pulsed laser 150 is incident on the inorganic film 130.

[0113] As previously discussed, the pulsed laser 150 is a pulsed laser characterized by a pulse duration and a repetition rate. The pulsed laser 150 may have a pulse duration and repetition rate sufficient to generate the plasma area in the weld region 160 between the first glass substrate 110 and the second glass substrate 120 and sufficient to heat a large volume of the glass proximate to the weld region 160. In embodiments, the pulsed laser 150 may have a pulse duration that is at least one order of magnitude greater than the pulse duration of ultrafast lasers (i.e., on the order of a few picoseconds), which are used in existing glass welding applications. In embodiments, the pulsed laser 150 may have a pulse duration of greater than or equal to about 0.5 nanoseconds (ns), greater than or equal to about 1 ns, or even greater than or equal to about 2 ns. In embodiments, the pulsed laser 150 may have a pulse duration of from about 0.5 ns to about 20 ns, from about 0.5 ns to about 15 ns, from about 0.5 ns to about 10 ns, from about 1 ns to about 20 ns, from about 1 ns to about 15 ns, from about 1 ns to about 10 ns, from about 1 ns to about 5 ns, from about 2 ns to about 20 ns, from about 2 ns to about 15 ns, from about 2 ns to about 10 ns, from about 2 ns to about 5 ns, or from about 5 ns to about 20 ns.

[0114] The pulsed laser 150 may have a repetition rate of greater than or equal to about 0.2 megahertz (MHz), such as greater than or equal to about 0.5 MHz, or even greater than or equal to about 1 MHz. In embodiments, the pulsed laser 150 may have a repetition rate of from about 0.2 MHz to about 50 MHz, from about 0.2 MHz to about 30 MHz, from about 0.2 MHz to about 20 MHz, from about 0.2 MHz to about 10 MHz, from about 0.5 MHz to about 50 MHz, from about 0.5 MHz to about 30 MHz, from about 0.5 MHz to about 20 MHz, from about 0.5 MHz to about 10 MHz, from about 1 MHz to about 50 MHz, from about 1 MHz to about 30 MHz, from about 1 MHz to about 20 MHz, from about 1 MHz to about 10 MHz, from about 2 MHz to about 50 MHz, from about 2 MHz to about 30 MHz, from about 2 MHz to about 20 MHz, from about 2 MHz to about 10 MHz, or from about 5 MHz to about 50 MHz.

[0115] The pulsed laser 150 may have a spot size of greater than or equal to about 50 micrometers (pm), such as greater than or equal to 100 pm, at the point where the pulsed laser 150 is incident on a surface of the inorganic fdm 130. In embodiments, the pulsed laser 150 may have a spot size of from about 50 pm to about 700 pm, from about 50 pm to about 500 pm, from about 50 pm to about 300 pm, from about 50 pm to about 200 pm, from about 100 pm to about 700 pm, from about 100 pm to about 500 pm, from about 100 pm to about 300 pm, or from about 100 pm to about 200 pm at the point where the pulsed laser 150 is incident on a surface of the inorganic film 130.

[0116] Referring again to FIG. 4, the pulsed laser 150 may be generated by a laser system 200 comprising a laser source 202 and an optical assembly 204. The laser source 202 and optical assembly 204 may be operable to produce the pulsed laser 150 having the properties disclosed herein and direct the pulsed laser 150 at the inorganic film 130 disposed between the first glass substrate 110 and the second glass substrate 120. The laser source 202 may be any laser source capable of producing the pulsed laser 150 that is a pulsed laser beam having wavelength, pulse duration, repetition rate, and power as previously discussed herein.

[0117] The optical assembly 104 may be positioned downbeam of the laser source 202 and may be operable to modify one or more characteristics of the pulsed laser 150, such as but not limited to beam shape, power density distribution, or other beam characteristics. The optical assembly 204 may be operable to direct the pulsed laser 150 to the weld stack 140 and the interface between the first glass substrate 110 and the second glass substrate 120. The optical assembly 204 may one or more shaping optics, turning mirrors, focusing mirrors, beam splitters, or combinations of these. In embodiments, the optical assembly 204 may comprise at least one focusing optic, at least one shaping optic, or both. The focusing optics may include one or more lenses, mirrors, or both that are operable to focus the beam of the pulsed laser 150. The shaping optics may include one or more lenses, mirrors, or both that are operable to modify a shape the pulsed laser 150. In embodiments, the optical assembly 204 may comprise one or more variable beam expanders (e.g., zoom telescope lenses), cylindrical lenses, aspheric- cylindrical lenses, polygon mirrors, or combinations thereof to modify a beam size, beam shape, beam power density distribution, or combinations thereof. The optical assembly 204 may include any other optical components, such as but not limited to mirrors, lenses, beam splitters, prisms, filters, apertures, etc., operable to modify one or more characteristics of the pulsed laser 150 upbeam of the weld stack 140.

[0118] The pulsed laser 150 may be positioned relative to the weld stack 140 so that the inorganic fdm 130 is disposed between the laser system 200 that produces the pulsed laser 150 and the focal point (i.e., beam waste) of the pulsed laser 150. In embodiments, the pulsed laser 150 may be positioned and focused so that pulsed laser 150 is incident on the inorganic fdm 130 at a point that is upbeam relative to the beam waste of the pulsed laser 150 and downbeam relative to the lenses in the optical assembly 204 of the laser system used to generate the pulsed laser 150.

[0119] Referring again to FIG. 4, in embodiments, the laser system 200 may be positioned to direct the pulsed laser 150 through the glass substrate to which the inorganic fdm 130 is applied. As shown in FIG. 4, in embodiments, the inorganic fdm 130 may be applied to the first surface 112 of the first glass substrate 110 and the laser system 200 may be positioned so that the pulsed laser 150 passes through the first glass substrate 110 before being incident on the inorganic fdm 130. In other words, the laser system 200 may be positioned so that the first glass substrate 110 is upbeam of the inorganic fdm 130. In embodiments, the laser system 200 may be positioned so that the pulsed laser 150 passes through the second glass substrate 120 before being incident on the inorganic fdm 130, which is deposited on the first surface 112 of the first glass substrate 110. Either orientation of the pulsed laser 150 will produce a weld between the first glass substrate 110 and the second glass substrate 120. However, it is preferred that the pulsed laser 150 pass through the glass substrate to which the inorganic fdm 130 is applied before being incident on the inorganic fdm 130.

[0120] As previously discussed, during welding, the pulsed laser 150 incident on the inorganic fdm 130, which absorbs the energy from the pulsed laser 150, melts, and generates heat at the interface between the first glass substrate 110 and the second glass substrate 120. The pulsed laser 150 with longer pulse duration of greater than or equal to about 0.5 ns, high repetition rate of greater than or equal about 0.2 MHz, and power of from about 2 W to about 50 W, in combination with the inorganic film 130, forms a very strong plasma area at the weld region 160 disposed at the interface between the first glass substrate 110 and the second glass substrate 120. The power, pulse duration, and repetition rate of the pulsed laser 150 disclosed herein may also increase the temperature of the glass in the first glass substrate 110, the second glass substrate 120, or both. As the temperature of the glass increases, the absorbance of the glass increases with respect to the pulsed laser 150, thereby further increasing the temperature of the glass. Moreover, the plasma generated by the inorganic fdm 130 also adsorbs into the first glass substrate 110 the second glass substrate 120, or both to further increase thetemperature in the glass. The greater volume of glass heated by the pulsed laser 150, which is indicated by stress area 162 in FIG. 4, may cause the first glass substrate 110, the second glass substrate 120, or both to thermally expand enough to close the gap G between the first glass substrate 110 and the second glass substrate 120 form a bond between the first glass substrate 110 and the second glass substrate 120 at the weld region 160. The bonding at the weld region 160 may be accomplished without application of external forces to the first glass substrate 110 and second glass substrate 120 to push the substrates together.

[0121] In embodiments, ULE glass can be welded to ULE glass or to fused silica by applying an inorganic film and using a pulsed laser having a longer wavelength, such as a wavelength of 532 nm. The ULE glass may comprise TiCh in addition to silica, and the presence of the TiCL may result in a strong absorption band encompassing the wavelength of 355 nm, thereby necessitating the laser having longer wavelength. In embodiments, the strong absorption of ULE glass at wavelength of 355 nm can be used to weld ULE glass to other ULE glass or to fused silica without using the inorganic film 130. In these embodiments, the methods disclosed herein may include providing a first glass substrate comprising fused silica or ULE glass and a second glass substrate comprising ULE glass and exposing the interface between the first glass substrate and the second glass substrate to the pulsed laser 150 having a wavelength of from about 200 nm to about 400 nm, a repetition rate of greater than about 0.2 MHz, and a pulse duration of greater than or equal to 0.5 ns. The greater absorption of the ULE glass generates greater heat within the glass, resulting in the thermal expansion sufficient to enable expansion across the gap and formation of the weld region between the two glass substrates.

[0122] Referring now to FIG. 5, the weld stack 140 and the pulsed laser 150 may be translated relative to one another to produce a weld line (e.g., weld line 164 in FIG. 1) between the first glass substrate 110 and the second glass substrate 120. Referring again to FIG. 5, in embodiments, the weld stack 140 may be stationary and the pulsed laser 150 maybe translated in a direction 210 relative to the weld stack 140, such as by translating the laser system 200 in the direction 210. The laser system 200 may be coupled to a positioning system (not shown) operable to position the laser system 200 and move the laser system 200 relative to weld stack 140. In embodiments, the laser system 200 may be stationary and the pulsed laser 150 may be translated relative to the weld stack 140 using one or more optical components, such as but not limited to a galvanometer, a polygon mirror, or other optical component or collection of optical components, which maybe part of the optical assembly 204. The direction 210 may be a lineardirection, curved path, or any suitable path shape. In embodiments, the laser system 200 may be stationary and the weld stack 140 may be moved in a direction 212 relative to the laser system 200. The direction 212 may be a linear direction, a curved path, or any other suitable path shape. In embodiments, the laser system 200 and the weld stack 140 may be translated relative to each other simultaneously.

[0123] A relative speed between the weld stack 140 and the pulsed laser 150 may be sufficient to bond the first glass substrate 110 and the second glass substrate 120 at the weld region 160 to form a weld line. In embodiments, the methods may include translating the pulsed laser 150, the weld stack 140, or both relative to one another at a relative speed of from about 1 mm / s to about 50 mm / s, such as from about 1 mm / s to 20 mm / s. In embodiments, once the weld line is complete, the pulsed laser 150, the weld stack 140, or both may be repositioned to produce a second weld line. The second weld line may be parallel to the first weld line. In embodiments, translating the pulsed laser 150 and the weld stack 140 relative to one another may be repeated at different locations to produce a plurality of weld lines. The plurality of weld lines may be parallel to one another. However, it is understood that different weld lines with different shapes, spacing, or orientation can be made using the systems and methods disclosed herein. The weld lines can be linear, curved, or have any desired shape.

[0124] Following welding, the weld stack 140 comprising the weld regions 160 and / or weld lines, may be allowed to cool to room temperature. In embodiments, outside of the weld regions 160, the inorganic film 130 may still be present on the first surface 112 of the first glass substrate 110 or the second surface 122 of the second glass substrate 120. The excess inorganic film 130 may be etched away by contacting the remaining portions of the inorganic film 130 with an etchant suitable for etching metals. Etchants may include strong acids, such as but not limited to HF or other mineral acids or organic acids suitable for etching metals. The contacting may comprise submerging the weld stack 140 comprising the one or more weld lines in a bath comprising an etchant solution.

[0125] In embodiments, the glass article 100 comprising the first glass substrate 110 and the second glass substrate 120 rigidly coupled to one another at one or more weld regions 160 or weld lines may be subjected to an annealing process. As described herein, increasing the volume of the first glass substrate 110, the second glass substrate 120, or both that heated by the pulsed laser 150 may create a stress region 162 within the first glass substrate 110 and / or the second glass substrate 120. These stress regions 162 can create birefringence regions withinthe first glass substrate 110 and / or second glass substrate 120. Annealing may reduce the stress in the stress regions of the first glass substrate and / or the second glass substrate, thereby reducing the birefringence in the glass.

[0126] Referring again to FIG. 1, the methods disclosed herein may be used to produce a glass article 100 comprising the first glass substrate 110 and the second glass substrate 120 rigidly coupled to each other by at least one weld region 160. The first glass substrate 110 and the second glass substrate 120 each may have a coefficient of thermal expansion of less than or equal to about 3 ppm / oC-1(3xl0-6°C1) in a temperature range of from -20 °C to 250 °C. The first glass substrate 110 and the second glass substrate 120 may have any of the compositions, features, or properties previously described herein for the glass substrates. In embodiments, the first glass substrate 110, the second glass substrate 120, or both may each be fused silica or ULE glass. In embodiments, the first glass substrate 110 and the second glass substrate 120 maybe either fused silica or ULE glass. In embodiments, the first glass substrate 110 may be fused silica or ULE glass, and the second glass substrate 120 may be unconsolidated silica soot or partially consolidated silica soot.

[0127] Referring to FIG. 2, the glass article 100 may comprise one or a plurality of weld lines 164 comprising a continuous weld region 160 extending along at least one weld path. In embodiments, the weld path of each weld line 164 is perpendicular to a line normal to the first surface 112 of the first glass substrate 110 at all points along the weld line 164. The weld path of each weld line 164 may be linear, curved in one or more directions, or have other suitable shape. In embodiments, the weld lines 164 may have a width equal to a width of the weld region, where the width is measured in a transverse direction across the weld region 160 perpendicular to the weld path. In embodiments, the weld region 160, the weld lines 164, or both may have a width W of greater than or equal to about 50 pm, greater than or equal to about 70 pm, or even greater than or equal to about 100 pm. In embodiments, the weld region 160, the weld lines 164, or both may have a width W of from about 50 pm to about 200 pm, from about 50 pm to about 150 pm, from about 50 pm to about 100 pm, from about 70 pm to about 200 pm, from about 70 pm to about 150 pm, from about 70 pm to about 100 pm, from about 100 pm to about 200 pm, or from about 100 pm to about 150 pm. The greater width of the weld lines 164 may provide increased strength compared to ultrafast laser welding, which has weld widths of less than about 20 pm at the most. The greater weld width of the weld lines 164 provided by the methods disclosed herein may enable the first glass substrate 110 and the second glass substrate 120 to be coupled together using fewer weld lines 164 compared to theother existing glass welding techniques having thinner weld lines. In embodiments, the glass article 100 may comprise a plurality of weld lines 164 parallel to one another along each weld path. Although shown in FIGS. 1 and 2 has having a plurality of weld lines 164, in embodiments, the glass article 100 may include only a single weld line at each location where the first glass substrate 110 and second glass substrate 120 are coupled.

[0128] Referring to FIGS. 1 and 2, when the glass article 100 comprises a plurality of weld lines 164, the weld lines 164 may be spaced apart from one another. In embodiments, the weld lines 164 may be spaced apart from one another by a distance of greater than or equal to about 1 pm, greater than or equal to about 5 pm, greater than or equal to about 10 pm, greater than or equal to about 20 pm, greater than or equal to about 50 pm, or even greater than or equal to about 100 pm. Outside of the weld regions 160, the glass of the first glass substrate 110 and / or the second glass substrate 120, which are low CTE glasses, are not heated sufficiently to cause enough thermal expansion in the glass to close the gap G between the first surface 112 and the second surface 122. Therefore, in the regions of the glass article 100 between or outside of the weld lines 164, the first glass substrate 110 and the second glass substrate 120 of the glass article 100 may be spaced apart by the gap G, which may comprise an average distance between the first surface 112 and the second surface 122 of from about 2 pm to about 10 pm, such as from about 2 pm to about 9 pm, from about 2 pm to about 8 pm, from about 2 pm to about 7 pm, from about 2 pm to about 6 pm, from about 2 pm to about 5 pm, from about 3 pm to about 10 pm, from about 3 pm to about 9 pm, from about 3 pm to about 8 pm, from about 3 pm to about 7 pm, from about 3 pm to about 6 pm, from about 3 pm to about 5 pm, or from about 5 pm to about 10 pm.

[0129] As previously discussed, exposing the weld stack 140 to the pulsed laser 150 causes heating of a greater volume of the glass proximate to the weld region 160 in the first glass substrate 110 and / or the second glass substrate 120. Referring again to FIG. I, the heating of the volume of glass produces a stress region 162 in the first glass substrate 110 and the second glass substrate 120 proximate to the weld region 160. The stress region 162 may have an amount of stress greater than the bulk glass of the first glass substrate 110 and the second glass substrate 120. The stress regions 162 are present in the first glass substrate 110 and / or the second glass substrate 120 after welding and prior to annealing. Annealing may reduce the stresses in the glass, thereby, reducing or eliminating the stress regions 162 in the glass. The stress regions 162 in the glass caused by the welding process disclosed herein can be identifiedthrough observed birefringence in the glass of the first glass substrate 110 and / or the second glass substrate 120.

[0130] In embodiments, the glass article 100, before annealing, may have an internal stress region 162 having a stress of greater than or equal to about 10 megapascals (MPa), greater than or equal to about 20 MPa, greater than or equal to about 30 MPa, or even greater than or equal to about 40 MPa. In embodiments, the stress in the internal stress regions 162 of the glass article 100, prior to annealing, may be from about 10 MPa to about 200 MPa, such as from about 10 MPa to about 100 MPa, from about 10 MPa to about 50 MPa, from about 10 MPa to about 40 MPa, from about 20 MPa to about 200 MPa, from about 20 MPa to about 100 MPa, from about 20 MPa to about 50 MPa, from about 20 MPa to about 40 MPa, from about 30 MPa to about 200 MPa, from about 30 MPa to about 100 MPa, from about 30 MPa to about 50 MPa, from about 30 MPa to about 40 MPa, from about 40 MPa to about 200 MPa, from about 40 MPa to about 100 MPa, from about 40 MPa to about 50 MPa, or from about 50 MPa to about 200 MPa.

[0131] As described herein, the "internal stress" is measured using birefringence. In particular, a 1 mm sample of a first glass substrate 110 and a second glass substrate 120 are welded and then cut with diamond cut saw to produce a cross-section transverse to the weld line. The resulting cross-section is mounted in a polarimeter to measure the optical birefringence resulting from local stress regions. The measured birefringence is converted into residual stress using the known stress optic coefficient of the first glass substrate 110 (e.g., the glass substrate through which the pulsed laser passed before being incident on the inorganic film).

[0132] The stress regions 162 in the glass article 100 may be asymmetric relative to the interface between the first glass substrate 110 and the second glass substrate 120. In other words, the stress regions 162 may be disposed more in one of the glass substrates over the other glass substrate. Referring to Fig. 4, in embodiments, the greater portion of the stress region 162 may be disposed in the glass substrate through which the pulsed laser 150 passes to get to the inorganic film 130. In the embodiment depicted in FIG. 4, the pulsed laser 150 passes through the first glass substrate 110 before being incident on the inorganic film 130. Without being bound by any particular theory, it is believed that the inorganic film 130 absorbs the pulsed laser 150, thereby at least partially or fully blocking penetration of the pulsed laser 150 into the second glass substrate 120 until the plasma is generated. Thus, during formation of the plasma,the first glass substrate 110 is preferentially heated in the regions proximate the weld region 160, which results in a greater proportion of the stress region 162 disposed in the first glass substrate 110 in FIG. 4 compared to the second glass substrate 120. In embodiments, at least 80%, at least 90%, at least 95%, or even at least 98% of the stress regions 162 in the glass article 100 may be disposed in either the first glass substrate 110 or the second glass substrate 120, depending on from which direction the pulsed laser 150 is directed at the inorganic film 130.

[0133] Referring again to FIG. I, the stress regions 162 in the glass article 100 may be elongated regions extending into the first glass substrate 110 or the second glass substrate 120 to a depth D of up to about 1 mm from the interface between the first glass substrate 110 and second glass substrate 120. In embodiments, the stress regions 162 may have an aspect ratio of from about 2 to about 10, such as from about 2 to about 5, from about 3 to about 10, from 3 to about 5, or from about 5 to about 10. The aspect ratio of the weld region 162 is equal to the depth D of the stress region 162 divided by the width Ws of the stress region. The depth D of the stress region 162 is a distance between a depth of the stress into the first glass substrate 110 and the depth of the stress into the second glass substrate 120 (i.e., the distance between the top and bottom of the stress region 162 in the + / -Z direction of the coordinate axis in FIG. 1). The width Ws of the stress region refers to the maximum width of the stress in a direction perpendicular to a direction of the weld line 164 (i.e., the maximum width of the stress region 162 in the + / -X direction of the coordinate axis in FIG. 1).

[0134] In embodiments, the weld region 160 sufficiently bonds the first glass substrate 110 and the second glass substrate 120 such that the welded glass article 100 has a surface energy bond strength greater than or equal to 0.2 J / cm2. In embodiments, the welded glass article 100 has a surface energy bond strength greater than or equal to 0.2 J / cm2and less than or equal to 3.0 J / cm2. In embodiments, the welded glass article 100 may have a surface energy bond strength greater than or equal to 0.2 J / cm2, greater than or equal to 0.5 J / cm2, greater than or equal to 0.8 J / cm2, greater than or equal to 1.0 J / cm2, greater than or equal to 1.2 J / cm2, or even greater than or equal to 1.5 J / cm2. In embodiments, the welded glass article 100 may have a surface energy bond strength less than or equal to 3.0 J / cm2, less than or equal to 2.5 J / cm2, or even less than or equal to 2.0 J / cm2.

[0135] The first glass substrate 110, the second glass substrate 120, or both may have metal particles, metal oxides, or both diffused into the first glass substrate 110, the second glasssubstrate 120, or both. The metal particles and / or metal oxides may originate from the inorganic fdm 130, which may be converted to a plasma and may diffuse into the first glass substrate 110 and / or the second glass substrate 120 during the welding process. The metal particles and / or the metal oxides may include any of the metals present in the inorganic film 130 prior to exposing the weld stack 140 to the pulsed laser 150. In embodiments, the metal particles and / or the metal oxides may comprise a metal selected from the group consisting of stainless steel, copper, chromium, chromiumoxynitride, aluminum, nickel, titanium, iron, and combinations thereof. The weld region 160, the stress region 162, or both may have a composition that is different from a bulk glass composition of the first glass substrate 110, the second glass substrate 120, or both. The difference in the composition in the weld region 160 and / or the stress region 162 (prior to annealing) are the result of metal particles and / or metal oxides from the inorganic film 130 diffusing in the first glass substrate 110 and the second glass substrate 120. However, the metal particles and / or the metal oxides from the inorganic film 130 do not diffuse throughout the entire first glass substrate 110 and second glass substrate 120, but diffuse only into heated regions of the glass substrates. Thus, the bulk composition of the first glass substrate 110 and the second glass substrate 120 may not have the metal particles and / or metal oxides resulting from diffusion of these species into the glass substrates. The difference in composition in the weld regions 160 and in the stress regions 162 are still present in the glass article 100 even after annealing and detectable via x-ray diffraction (XRD) or other analytical techniques in the finished glass articles 100. The glass articles 100 may have distinct first regions comprising he metal particles and / or metal oxides from the inorganic film 130 and second regions without the metal particles and / or metal oxides.

[0136] The glass articles 100, after welding and removal of any residual inorganic film 130 in the spaces between weld lines 164, may be transparent to light in the visible spectrum. In embodiments, the glass articles 100 may have a transmissivity for light having wavelengths of from about 380 nm to about 700 nm of greater than or equal to about 90%, greater than or equal to about 95%, greater than or equal to about 98%, or even greater than or equal to about 99%. The presence of the metal particles and / or metal oxides from the inorganic film 130 diffused into the first glass substrate 110 or the second glass substrate 120 may have very little influence on the transparency of the glass articles 100.

[0137] The glass articles 100 disclosed herein comprising the first glass substrate 110 and the second glass substrate 120 coupled together at the weld region 160 may be useful for producing optical components, glass fiber preforms, or other glass articles. The methodsdisclosed herein may be used to produce larger size optical components by welding multiple glass substrates together. For instance, the methods disclosed herein can be used to join a plurality of glass parts together to form a larger optical elements, such as by tiling smaller parts together to produce a larger mirror structure or other larger optical element. In embodiments, the glass articles 100 may also be useful as glass fiber preforms, which can then be used to produce optical fibers through heating and drawing of the glass fiber preform.

[0138] Test Methods

[0139] Weld Strength Test

[0140] Referring now to FIG. 6, a surface energy bond strength of the welded glass article 100 may be determined according to a "razor blade test." In particular, a razor blade 220 with a known thickness is inserted between the first glass substrate 100 and the second glass substrate 120, both of which have known fracture mechanic material properties, until crack formation occurs. The resulting crack length L from the razor blade edge 222 to the remaining sealed portion is used to calculate the surface energy bond strength y using the following equation 1 (EQU. 1).

[0141] In EQU. 2, tb is the thickness of the razor blade 220, L is the crack length, Ei is the Young’s modulus of the first glass substrate 110, E2 is the Young’s modulus of the second glass substrate 120, twiis the thickness of the first glass substrate 110, and tW2 is the thickness of the second metal substrate 120.EXAMPLES

[0142] The various embodiments of the systems and methods disclosed herein will be further clarified by the following examples. The examples are illustrative in nature, and should not be understood to limit the subject matter of the present disclosure.

[0143] Example 1: Weldins Fused Silica Using Stainless Steel as the Inorganic Film

[0144] In Example 1 , two fused silica substrates were welded together along multiple weld lines using an inorganic film comprising stainless steel. For Example I, the first glass substrate and second glass substrate were both fused silica. Referring to FIG. 3, the stainless steel coatingwas applied to the first surface 112 of the first glass substrate 110. The thickness of the stainless steel coating was 40 nm. The first glass substrate 110 was placed on top with the inorganic film comprising the stainless steel facing downward (i.e., in the -Z direction of FIG. 3). The second glass substrate 120 was placed underneath the first glass substrate 110 with the second surface 122 facing toward the inorganic film 130. The pulsed laser 150 having wavelength of 355 nm, a power of 25 W, a pulse duration of 2 ns, and repetition rate of 2 MHz was directed towards the inorganic film from above, resulting in the pulsed laser 150 passing through the first glass substrate before being incident on the inorganic film 130. No pressure was applied to the weld stack during the welding. The pulsed laser 150 was translated at a linear speed of 5 mm / s to produce a weld line coupling the first glass substrate and the second glass substrate. The welding was repeated a number of times to produce a welded glass article comprising a plurality of parallel weld lines.

[0145] The temperature generated by the laser during welding was recorded by a spectrometer. Referring to FIG. 7, the emissions from the welding area and corresponding black body radiation at 4200 C is graphically depicted. FIG. 7 demonstrates that the peak temperature in the glass achieved by the process can be much greater than the melting temperature of the glass, but less than the ablation temperature.

[0146] The welded glass article of Example 1 was sectioned perpendicular to the plurality of weld lines, before annealing. Referring now to FIG. 8, an image of the cross-section of the welded glass article was taken with polarized light to reflect the birefringence in the glass generated by the welding process. As shown in FIG. 8, the welding process produce the stress regions 162 in the glass extending into the first glass substrate 110 to a depth of 0.5 mm. The dark regions at the interface indicate the weld regions 160 where the first glass substrate 110 and the second glass substrate 120 were coupled.

[0147] The image of the cross-section of the welded glass article of Example 1 was analyzed to estimate the amount of expansion of the glass to close the gap between the first glass substrate and the second glass substrate at the weld region 160. The analysis indicated that glass expanded by a distance of from about 2 pm to about 3 pm. The distance between the glass substrates measured by this test may be less than the actual distance between the two glass substrates prior to welding. Without being bound by any particular theory, it is believed that the distance between the substrates after welding, as determined from the image analysis,may be less than the distance between the glass substrates before welding due to the greater viscosity of the glass in hot state and dynamics of glass flow during the welding process.

[0148] Unlike in case of higher CTE glass, for the fused silica of Example 1 having low CTE, the internal stresses created in the glass by the thermal expansion are moderate considering the much larger volume of glass heated in Example 1 compared to the volume heated when welding high CTE glasses using existing methods. Referring now to FIGS. 9 and 10, the internal stress in the stress regions 162 of the welded glass article of Example 1 was evaluated. FIG. 9 shows the birefringence of the welded glass article as a function of location within the glass article. From the birefringence fields in FIG. 9, the internal stress within the welded glass article was determined for multiple points within the welded glass article. The results of the internal stress (y-axis) as a function of position within the glass (x-axis) are provided in FIG. 10. As shown in FIG. 10, the maximum internal stress within the welded glass article is about 40 MPa, which is located at the point equal to the greatest depth of the stress region in the first substrate.

[0149] The welded glass article of Example 1 was then subjected to the weld strength test described herein. The weld regions 160 in the welded glass article of Example 1 were strong enough so that the glass failed before the weld region 160 when the razor blade was inserted between the first glass substrate 110 and the second glass substrate 120.

[0150] Example 2: Closely Spaced Weld Lines

[0151] In Example 2, the first glass substrate and second glass substrate were welded together according to the methods described in Example 1 using stainless steel as the inorganic film. For Example 2, the weld lines were closely spaced together. The welded glass article of Example 2 was sectioned perpendicular to the plurality of weld lines, before annealing. Referring now to FIG. 11, an image of the cross-section of the welded glass article of Example 2 was taken with polarized light to reflect the birefringence in the glass generated by the welding process. As shown in FIG. 11 , the methods disclosed herein can be used to produce weld lines that are close together such that a distance between weld lines may be less than or equal to the width of the weld lines themselves.

[0152] Example 3: Weldins Fused Silica Using Stainless Steel as the Inorganic Film

[0153] In Example 3, two fused silica substrates were welded together along multiple weld lines using an inorganic film comprising copper. For Example I, the first glass substrate and second glass substrate were both fused silica. Referring to FIG. 3, the inorganic film 130 wascopper and was applied to the first surface 112 of the first glass substrate 110. The thickness of the copper coating was 40 nm. The first glass substrate 110 was placed on top with the inorganic film comprising the stainless steel facing downward (i.e., in the -Z direction of FIG. 3). The second glass substrate 120 was placed underneath the first glass substrate 110 with the second surface 122 facing toward the inorganic film 130. The pulsed laser 150 having wavelength of 355 nm, a power of 25 W, a pulse duration of 2 ns, and repetition rate of 2 MHz was directed towards the inorganic film from above, resulting in the pulsed laser 150 passing through the first glass substrate 110 before being incident on the inorganic film 130. No pressure was applied to the weld stack during the welding. The pulsed laser 150 was translated at a linear speed of 5 mm / s to produce a weld line coupling the first glass substrate and the second glass substrate.

[0154] The welded glass article of Example 3 was sectioned perpendicular to the plurality of weld lines, before annealing. Referring now to FIG. 12, an image of the cross-section of the welded glass article was taken with polarized light to reflect the birefringence in the glass generated by the welding process. As shown in FIG. 12, the welding process of Example 3 using copper as the inorganic film 130 exhibited an even larger laser interaction zone compared to the welded glass article of Example 1 (stainless steel inorganic film). The larger laser interaction zone resulted in a stress region 162 extending to a depth of about 1 mm into the first glass substrate 110, which is almost twice the depth of the stress region in the welded glass article of Example 1. In some cases, it was observed that the stress region 162 of the welded glass article of Example 3 reached the outer surface of the first glass substrate 110 when copper was used as the inorganic film 130. Without being bound by any particular theory, it is believed that the greater depth of the stress region 162 may be due to oxidation of copper at high temperature and variable absorption of the copper into the first glass substrate due to the elevated temperature.

[0155] Example 4: Weldins Fused Silica to Partially Consolidated Silica Soot

[0156] In Example 4, welding of fused silica to unconsolidated silica soot was demonstrated. Unconsolidated silica soot has a greater surface roughness compared to fused silica, and therefore, is generally unsuitable for any welding process requiring optical contact or close contact of less than about 1 pm. For Example 4, the first glass substrate was the fused silica and the second glass substrate was partially consolidated silica soot having a density greater than about 1.2 g / cm3. Referring again to FIG. 3, the inorganic film 130 was stainlesssteel having a thickness of 40 nm and was applied to the first surface 112 of the first glass substrate 110. The first glass substrate 110 was placed on top with the inorganic film comprising the stainless steel facing downward (i.e., in the -Z direction of FIG. 3). The second substrate 120, which comprised the partially consolidated silica soot, was placed underneath the first glass substrate 110 with the second surface 122 facing toward the inorganic film 130. The pulsed laser 150 having wavelength of 355 nm, a power of 25 W, a pulse duration of 2 ns, and repetition rate of 2 MHz was directed towards the inorganic film from above, resulting in the pulsed laser 150 passing through the first glass substrate 110 before being incident on the inorganic film 130. No pressure was applied to the weld stack during the welding. The pulsed laser 150 was translated at a linear speed of 5 mm / s to produce a weld line coupling the first glass substrate and the second substrate.

[0157] The welding process of Example 4 resulted in a stable weld created between the fused silica of the first glass substrate and the partially consolidated silica soot of the second substrate. Referring now to FIG. 13, a photographic image of the weld line for the welded glass article of Example 4 is shown. In FIG. 13, the white area corresponds to the partially consolidated silica soot of the second substrate 120 and the dark area is the weld region 160. The width of the weld region in single scan was about 0.7 mm. The regular blade test was not applied to the welded glass article of Example 4 because the modulus of the partially consolidated soot is not well defined. However, the welded glass article of Example 4 appeared to be strong enough for general type handing. The ability to weld unconsolidated silica soot or partially consolidated silica soot to fused silica may be useful for certain applications, such as but not limited to providing for attachment of handholds for soot blanks in fiber optics operations.

[0158] Example 5: Weldins o f ULE Glass to Fused Silica with No Inorganic Film

[0159] In Example 5, a ULE glass substrate was welded to a fused silica substrate together along multiple weld lines without using an inorganic film disposed between the two substrates. For Example 5, the first glass substrate was ULE® glass and the second glass substrate was fused silica glass, both produced by Coming Incorporated. The weld stack was positioned relative to the pulsed laser so that the pulsed laser passed through the second glass substrate comprising the fused silica before reaching the interface.

[0160] ULE glass has greater UV absorption of laser light at 355 nm, which is why it is possible to weld fused silica to the ULE glass without using the inorganic film to absorb thelaser light to start the heating process. In Example 5 the UV laser 150 had a wavelength of 355 nm, a power of 25 W, a pulse duration of 2 ns, and repetition rate of 2 MHz. The pulsed laser 150 was directed so that the laser beam passed through the fused silica of the first glass substrate before reaching the interface between the first glass substrate and the second glass substrate. No pressure was applied to the weld stack during the welding. The pulsed laser 150 was translated at a linear speed of 5 mm / s to produce a weld line coupling the first glass substrate and the second glass substrate. The welding was repeated a number of times to produce a welded glass article comprising a plurality of parallel weld lines.

[0161] The welding process of Example 5 resulted in a strong and stable weld created between the ULE glass substrate and the fused silica. However, due to longer penetration of the pulsed laser with wavelength of 355 nm below interface and into the ULE glass (no absorbing film), the stability of welding process was more difficult to control. Referring now to FIG. 14, a photographic images of the weld region 160 indicates the formation of bubbles 170 on the ULE glass side, which are believed to be due to lower melting temperature of the ULE glass compared to the fused silica.

[0162] Example 6: ULE Glass to Fused Silica Using the Inorganic Film

[0163] In Example 6, fused silica was welded to ULE glass along multiple weld lines using an inorganic film comprising stainless steel. For Example 6, the first glass substrate was the fused silica and the second glass substrate was ULE® glass from Coming Incorporated. Referring again to FIG. 3, the stainless steel coating was applied to the first surface 112 of the first glass substrate 110. The thickness of the stainless steel coating was 40 nm. The first glass substrate 110 was placed on top with the inorganic film comprising the stainless steel facing downward (i.e., in the -Z direction of FIG. 3). The second glass substrate 120 was placed underneath the first glass substrate 110 with the second surface 122 facing toward the inorganic film 130.

[0164] ULE glass has greater UV absorption of laser light at 355 nm. However, since the pulsed laser was passing through the fused silica of the first glass substrate, the pulsed laser having wavelength of 355 was used. In Example 6, the pulsed laser 150 having wavelength of 355 nm, a power of 25 W, a pulse duration of 2 ns, and repetition rate of 2 MHz was directed towards the inorganic film from above, resulting in the pulsed laser 150 passing through the first glass substrate before being incident on the inorganic film 130. No pressure was applied to the weld stack during the welding. The pulsed laser 150 was translated at a linear speed of 5mm / s to produce a weld line coupling the first glass substrate and the second glass substrate. The welding was repeated a number of times to produce a welded glass article comprising a plurality of parallel weld lines.

[0165] In Example 6, the welding process produced a strong and stable weld between the fused silica and the ULE glass without using external pressure to force close contact between the glass substrates. The welded glass article of Example 6 was sectioned perpendicular to the plurality of weld lines, before annealing. Referring now to FIG. 15, an image of the crosssection of the welded glass article of Example 6 was taken with polarized light to reflect the birefringence in the glass generated by the welding process. As shown in FIG. 15, process generated a small bubble at the weld region 160 where the first glass substrate 110 and the second glass substrate 120 were coupled. Without being bound by any particular theory, it is believed that the small bubble at the weld region 160 is likely due to overheating of the ULE glass by the laser (for ULE melting temperature is 1490 °C, while for fused silica the melting temperature is about 1700 °C).

[0166] Referring now to FIG. 16, a photograph taken without the polarized light is provided to show the bubble at the weld region without the birefringence showing the stress regions.

[0167] While various embodiments of the glass articles and methods have been described herein, it should be understood that it is contemplated that each of these embodiments and techniques may be used separately or in conjunction with one or more embodiments and techniques.

[0168] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A method for welding low thermal expansion glass, the method comprising: applying an inorganic film on a first surface of a first glass substrate; positioning a second glass substrate with a second surface of the second glass substrate facing towards the first surface of the first glass substrate, wherein and the first surface and the second surface spaced apart by a distance of up to about 10 pm and the first glass substrate and the second glass substrate each comprise a low thermal expansion glass having a coefficient of thermal expansion of less than or equal to about 3 ppm / oC-1(3xl0-6°C1) in a temperature range of from -20 °C to 250 °C; and exposing one side of the inorganic film to a pulsed laser having a power of greater than about 2 W, a pulse duration of greater than or equal to about 0.5 ns, and a repetition rate of greater than or equal to about 0.2 MHz, wherein exposing the inorganic film to the pulsed laser heats and melts the inorganic film and heats the first glass substrate, the second glass substrate, or both to produce a glass article comprising the first glass substrate and the second glass substrate rigidly joined at a weld region.

2. The method of claim 1, wherein the low thermal expansion glasses of the first glass substrate and the second glass substrate each have a coefficient of thermal expansion less than or equal to about 2xl0-6°C1, or from about 0.05xl0-6°C1to about 3xl0-6°C1, or from about 0.1x1 O’6°C"1to about 2x1 O’6°C"1at a temperature range of from -20 °C to 250 °C.

3. The method of claim 1, wherein the low thermal expansion glass of the first glass substrate, the second glass substrate, or both have a softening point temperature of greater than or equal to about 1300 °C, greater than or equal to about 1400 °C, greater than or equal to about 1500 °C, greater than or equal to about 1600 °C, greater than or equal to about 1700 °C, or from about 1300 °C to about 1900 °C, or from about 1700 °C to about 1900 °C.

4. The method of claim 1 , wherein the first glass substrate, the second glass substrate, or both comprise fused silica or doped fused silica.

5. The method of claim 1, wherein the first glass substrate, the second glass substrate, or both comprise an Ultra Low Expansion (ULE) glass.

6. The method of claim 1, wherein the first glass substrate is fused silica or ULE glass and the second substrate is unconsolidated silica soot.

7. The method of claim 1, wherein the pulsed laser has a wavelength of from about 260 nm to about 1100 nm, from about 355 nm to about 532 nm.

8. The method of claim 1, wherein the first glass substrate and the second glass substrate are both transparent to the pulsed laser at a wavelength of the pulsed laser.

9. The method of claim 1, wherein the power of the pulsed laser is from about 2 W to about 50 W, such as from about 5 W to 50 W, or from about 10 W to about 50 W.

10. The method of claim 1 , wherein the pulsed laser has an energy density of less than about 25 J / cm2, such as from about 0.05 J / cm2to about 25 J / cm2.

11. The method of claim 1 , wherein the pulsed laser has a pulse duration of from about 0.5 nanoseconds (ns) to about 20 ns, such as from about 1 ns to about 20 ns, from about 2 ns to about 20 ns.

12. The method of claim 1, wherein the repetition rate of the pulsed laser is greater than or equal to about 1 MHz, or from about 0.2 MHz to about 50 MHz, from about 0.5 MHz to about 30 MHz, or from about 1 MHz to about 10 MHz.

13. The method of claim 1 , wherein the pulsed laser has a spot size of from about 50 pm to about 700 pm at the point where the pulsed laser is incident on the inorganic film.

14. The method of claim 1, wherein the pulsed laser is positioned so that the inorganic film is positioned between a lens of a laser system that produces the pulsed laser and a focal point of the pulsed laser.

15. The method of claim 1, wherein the inorganic film comprises a metal coating comprising one or more metals that: absorb light in a wavelength of from about 260 nm to about 1200 nm or from about 260 nm to about 550 nm with an absorbance of greater than 10% : have high transmission of light when diffused into the first glass substrate, the second glass substrate, or both, where high transmission is a transmission of greater than or equal to 99%; and can be etched by HF.

16. The method of claim 1, wherein the inorganic film comprises a metal coating comprising a metal having a melting temperature less than a melting temperature of the first glass substrate and the second glass substrate, such as melting temperature of from about 400 °C to about 900 °C, such as from about 500 °C to about 600 °C.

17. The method of claim 1, wherein the inorganic film comprises a metal coating comprising a metal selected from the group consisting of stainless steel, copper, chromium, nickel, titanium, aluminum, chromiumoxynitride (CrON), iron, and alloys thereof.

18. The method of claim 1, wherein the inorganic film is a metal coating comprising, consisting of, or consisting essentially of stainless steel, copper, chromium, an alloy of chromium and chromiumoxynitride (CrON), nickel, titanium, aluminum, iron, or an alloy of nickel and aluminum.

19. The method of claim 1, wherein the inorganic film has a thickness of less than about 500 nm, less than about 200 nm, less than about 100 nm, less than about 50 nm, less than about 20 nm, or from about 10 nm to about 500 nm.

20. The method of claim 1, wherein applying the inorganic film comprises sputtering or vapor deposition of a metal coating onto the first surface of the first glass substrate.

21. The method of claim 1, further comprising translating the pulsed laser or the first and second substrates relative to one another to produce a weld line between the first substrate and the second substrate.

22. The method of claim 21, comprising translating the pulsed laser or the first and second substrates relative to one another at a relative speed of from about 1 mm / s to about 50 mm / s, such as from about 1 mm / s to 20 mm / s.

23. The method of claim 21, comprising repeating the translating the pulsed laser of the first and second substrates relative to one another to produce a plurality of weld lines spaced apart from one another.

24. The method of claim 21, wherein each weld line has a width of from about 50 pm to about 200 pm, such as from about 100 pm to about 200 pm.

25. The method of claim 1, wherein the method does not required the first glass substrate and the second glass substrate to be in optical contact.

26. The method of claim 1 , further comprising removing residual inorganic film by etching with a metal etchant.

27. A glass article produced by the method of claim 1.

28. The glass article of claim 27, wherein the glass article is transparent.

29. The glass article of claim 27, wherein the glass article comprises one or more weld lines.

30. The glass article of claim 29, wherein each of the weld lines has a width of from about 50 pm to about 200 pm, such as from about 100 pm to about 200 pm.

31. The glass article of claim 29, wherein between each of the weld lines, the first glass substrate and the second glass substrate are separated by a distance of from about 2 pm to about 10 pm, or from about 5 pm to about 10 pm.

32. The glass article of claim 27, wherein the glass article, before annealing, exhibits an internal stress region having a stress of greater than or equal to about 10 MPa, greater than or equal to about 20 MPa, greater than or equal to about 30 MPa, or greater than or equal to about 40 MPa.

33. The glass article of claim 32, wherein the stress region is asymmetric relative to the interface between the first glass substrate and the second glass substrate.

34. The glass article of claim 33, wherein at least 90 % of the stress region is disposed in the first glass substrate or the second glass substrate.

35. The glass article of claim 27, wherein the first glass substrate and the second glass substrate comprise metal particles or metal oxides from the inorganic film diffused into the first glass substrate and the second glass substrate.

36. The glass article of claim 27, wherein the weld region has a composition different from a bulk composition of the first glass substrate, the second glass substrate, or both.

37. The glass article of claim 36, wherein the composition of the weld region comprises metal particles, metal oxides, or both from the inorganic film diffused into the first glass substrate, the second glass substrate, or both, wherein the metal particles, metal oxides, or both in the weld region are not present in the bulk composition of the first glass substrate, the second glass substrate, or both.

38. The glass article of claim 27, wherein a stress region of the weld region has a ratio of depth to width of from 2 to 10, wherein the ratio of depth to width is the depth of the stress in the stress region divided by the width of the stress in the stress region, the depth of the stress in the stress region is a distance between a depth of the stress into the first glass substrate and the depth of the stress into the second glass substrate, and the width of the stress in the stress region is the width of the stress in a direction perpendicular to a direction of a weld line.

39. The glass article of claim 27, wherein the glass article is a glass fiber preform.

40. The glass article of claim 27, wherein the glass article is an optical component.

41. A glass article comprising a first glass substrate and a second glass substrate rigidly coupled to each other by at least one weld region, wherein: the first glass substrate and the second glass substrate each have a coefficient of thermal expansion of less than or equal to about 3 ppmAC"1(3x1 O’6°C"1) in a temperature range of from -20 °C to 250 °C; and wherein the first glass substrate and the second glass substrate comprise metal particles or metal oxides diffused into the first glass substrate and the second glass substrate; and the metal particles or metal oxides comprise a metal selected from the group consisting of stainless steel, copper, chromium, chromiumoxynitride, aluminum, nickel, titanium, iron, and combinations thereof.

42. The glass article of claim 41, wherein the glass article is transparent.

43. The glass article of claim 41, wherein the glass article comprises one or more weld lines.

44. The glass article of claim 43, wherein each of the weld lines has a width of from about 50 pm to about 200 pm, such as from about 100 pm to about 200 pm.

45. The glass article of claim 43, wherein between each of the weld lines, the first glass substrate and the second glass substrate are separated by a distance of from about 2 pm to about 10 pm, or from about 5 pm to about 10 pm.

46. The glass article of claim 41, wherein the glass article, before annealing, exhibits an internal stress region having a stress of greater than or equal to about 10 MPa, greater than or equal to about 20 MPa, greater than or equal to about 30 MPa, or greater than or equal to about 40 MPa.

47. The glass article of claim 46, wherein the stress region is asymmetric relative to the interface between the first glass substrate and the second glass substrate.

48. The glass article of claim 47, wherein at least 90 % of the stress region is disposed in the first glass substrate or the second glass substrate.

49. The glass article of claim 41, wherein the metal particles or oxides are diffused into the first glass substrate, the second glass substrate, or both to a depth of less than or equal to about 1 pm from the interface between the first glass substrate and the second glass substrate.

50. The glass article of claim 41, wherein a stress region of the weld region has a ratio of depth to width of from 2 to 10, wherein the ratio of depth to width is the depth of the stress in the stress region divided by the width of the stress in the stress region, the depth of the stress in the stress region is a distance between a depth of the stress into the first glass substrate and the depth of the stress into the second glass substrate, and the width of the stress in the stress region is the width of the stress in a direction perpendicular to a direction of a weld line.

51. The glass article of claim 41, wherein the glass article is a glass fiber preform.

52. The glass article of claim 41, wherein the glass article is an optical component.

53. A method for welding low thermal expansion glass, the method comprising: providing a first glass substrate comprising an ultra-low expansion glass (ULE glass); providing a second glass substrate comprising a ULE glass or fused silica; positioning the second glass substrate with a second surface of the second glass substrate facing towards a first surface of the first glass substrate, wherein and the first surface and the second surface spaced apart by a distance of up to about 10 pm and the first glass substrate and the second glass substrate each have acoefficient of thermal expansion of less than or equal to about 3 ppm / oC-1(3x10" 6 °C1) in a temperature range of from -20 °C to 250 °C; and exposing an interface between the first glass substrate and the second glass substrate to a pulsed laser having a wavelength of from about 260 nm to about 400 nm, a power of greater than about 2 W, a pulse duration of greater than or equal to about 0.5 ns, and a repetition rate of greater than or equal to about 0.2 MHz, wherein exposing the heats the first glass substrate, the second glass substrate, or both to produce a glass article comprising the first glass substrate and the second glass substrate rigidly joined at a weld region.

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