Diffraction, beauty and commerce

What do a South American butterfly, an Australian banknote, a European moth and an international credit card have in common? The answer is they all use sub-micron grating microstructures as sophisticated optical components to achieve unique visual effects which are difficult to realize with more conventional optics. There is, however, a basic difference between these diffractive optical elements – the visual effect of the credit card hologram or the banknote diffraction grating is viewed in the first diffraction order, whereas the butterfly and moth structures are so fine that there is no first order under normal viewing conditions and the optical behaviour is seen primarily in the zero order (figure 1).