Patent ID: 7355944

Claim:
A method for using an optical article, comprising: illuminating a first portion of the optical article with a first laser to obtain a first optical signal, wherein the first laser has a first wavelength; illuminating a second portion with a second laser to obtain a second optical signal, wherein the second laser has a second wavelength that is different from the first wavelength; and determining if the optical article is authentic by comparing the first optical signal and the second optical signal; wherein the first optical signal is selected from the group consisting of reflectivity, transmission, luminescence, polarization, phase, and combinations comprising at least one of these optical signals, and wherein comparing the first optical signal to the second optical signal further comprises determining a ratio of the first optical signal to the second optical signal, and wherein if the ratio is greater than or equal to about 1.15 or less than or equal to about 0.85, the optical article is authentic.