Optical authentication

An apparatus may be provided for determining a signature from an article in a reading volume of the apparatus. The apparatus can comprise a source operable to generate a coherent beam and a beam directing member operable to direct the coherent beam into the reading volume. The apparatus may also comprise a detector arrangement for collecting signals created by scatter of the coherent beam within the reading volume, wherein different ones of the signals relate to scatter from different parts of the reading volume, the detector arrangement having a numerical aperture greater than a predetermined minimum and a processor operable to determine a signature for an article in the reading volume from the collected signals. Use of such apparatus can be repeated whenever required to test authenticity of the article. Using this system, it has been discovered that it is essentially pointless to go to the effort and expense of making specially prepared tokens, since unique characteristics are measurable in a straightforward manner from a wide variety of every day articles.