Method of separating strengthened glass

A method of separating a strengthened glass sheet into at least two pieces, the method comprising:

• a. providing the strengthened glass sheet,
• wherein said glass is an alkali aluminosilicate glass
• wherein said glass sheet has been strengthened by thermal tempering or by ion exchange in a molten salt bath;
• wherein the strengthened glass sheet has a strain point, an anneal point, a thickness, and a first surface and a second surface that are substantially parallel to each other and joined by a plurality of edges,
• wherein due to said strengthening at least one of the first surface and the second surface has a strengthened surface layer under a compressive stress of at least about 200 MPa, the strengthened surface layer extending at least about 20 μm from the respective surface to a depth of layer;
• wherein due to said strengthening a central region of the glass sheet is under a tensile stress, the central region located within the glass sheet between the first surface and the second surface and at a depth greater than the depth of layer,
• b. initiating a flaw at a flaw depth within the central region of the strengthened glass sheet, wherein the flaw is initiated by laser pulses having nanosecond length or less;
• c. forming a vent in the strengthened glass sheet by heating the surface of the strengthened glass sheet with a CO2 laser beam having a wavelength of 10.6 μm at the location of the initial flaw followed by quenching at the location of the initial flaw to at least partially separate the strengthened glass sheet into the at least two pieces, wherein the vent originates at the initial flaw and wherein said vent is propagated from the initial flaw in a separation direction along the strengthened glass sheet at a vent depth that is greater than or equal to the depth of layer by translating the strengthened glass sheet or by translating the laser beam across one of the first surface and the second surface.