US 11,884,091 B2
Diffractive structures within polymer substrates, their manufacture and use
Charles Douglas Macpherson, Santa Barbara, CA (US); Badr Omrane, Ottawa (CA); Peter Herman, Toronto (CA); Stephen Ho, Richmond Hill (CA); and Sean Magnus Malmberg, Ottawa (CA)
Assigned to Bank of Canada, Ottawa (CA); and The Governing Council of the University of Toronto, Toronto (CA)
Appl. No. 17/619,296
Filed by Bank of Canada, Ottawa (CA); and The Governing Council of the University of Toronto, Ottawa (CA)
PCT Filed Jun. 25, 2020, PCT No. PCT/CA2020/050884
§ 371(c)(1), (2) Date Dec. 15, 2021,
PCT Pub. No. WO2020/257935, PCT Pub. Date Dec. 30, 2020.
Claims priority of provisional application 62/866,693, filed on Jun. 26, 2019.
Prior Publication US 2022/0258523 A1, Aug. 18, 2022
Int. Cl. B42D 25/41 (2014.01); B42D 25/328 (2014.01); B23K 26/354 (2014.01); B23K 26/359 (2014.01); B42D 25/435 (2014.01); B42D 25/29 (2014.01); B41M 3/14 (2006.01)
CPC B42D 25/435 (2014.10) [B23K 26/354 (2015.10); B23K 26/359 (2015.10); B41M 3/144 (2013.01); B42D 25/29 (2014.10); B42D 25/328 (2014.10); B42D 25/41 (2014.10)] 26 Claims
OG exemplary drawing
 
1. A method for the manufacture of a security document or security device, the method comprising the steps of:
providing a substrate sheet comprising a substrate sheet material;
irradiating the substrate sheet at a plurality of discrete positions across a planar side of the substrate sheet corresponding to a two-dimensional array, with a laser beam from a femtolaser, whilst modifying the shape of the laser beam prior to its interaction with the substrate sheet so that the incident laser light is at least partially distributed along and / or about a laser propagation path extending within the substrate sheet;
to at least partially or temporarily melt, displace or decompose at least a portion of the substrate material at or within an elongate volume of the substrate sheet material about the laser beam longitudinal axis, corresponding to each of said discrete positions,
thereby to generate an array of laser-modified tracks within the substrate material,
each laser-modified track comprising an elongate volume of modified substrate material at least 4 times longer than its width extending at least partially across a thickness of the substrate sheet, where the modified form of the substrate material has a refractive index that is different to the general refractive index n of the unmodified substrate;
wherein each two-dimensional ordered array of laser-modified tracks thus produced collectively diffract light impinging on the substrate sheet to form an observable shape, image, or region of colour.