Patent ID: 8828284

Claim:
A method of producing an optical element having a mark comprising: (a) irradiating at least a portion of a surface of said optical element with laser radiation, thereby forming a plurality of elongated grooves in said portion of said surface, wherein, each elongated groove has a longitudinal axis, each elongated groove is substantially parallel to an adjacent elongated groove, the longitudinal axis of each elongated groove is aligned substantially parallel with a common longitudinal direction that extends from a center point of said plurality of elongated grooves, and said plurality of elongated grooves together define said mark; and (b) forming a clear film over at least said portion of said surface and said plurality of elongated grooves, wherein, said mark is substantially unobservable when a source of electromagnetic energy is viewed through said optical element at a first position that has a first alignment with said center point that is substantially parallel to said common longitudinal direction, and said mark is substantially observable when said source of electromagnetic energy is viewed through said optical element at a second position that has a second alignment with said center point that is substantially orthogonal to said common longitudinal direction.