Authentication apparatus and method

An authentication apparatus operative to determine the authenticity of a polymer film, comprising an optically-based birefringence measuring apparatus comprising:

• means to expose the film to a first light source of a first wavelength or range of wavelengths;
• means to expose the film to a second light source of a second wavelength or range of wavelengths, the first wavelength or range of wavelengths being different from the second wavelength or range of wavelengths;
• means to measure a first effect influenced by a birefringence characteristic of the film responsive to said first light source and to produce a first measured effect;
• means to measure a second effect influenced by a birefringence characteristic of the film responsive to said second light source and to produce a second measured effect;
• means to compare a value or range of values representative of a comparison between the first and second measured effects with a value or range of values representative of a comparison between a specified first effect and a specified second effect corresponding to a predetermined birefringence characteristic of an authentic polymer film responsive to the first and second light sources;
• and
• means to output an authenticity signal indicative of authenticity or otherwise of the film based upon one or more of the comparisons.