Many studies have focused on the use of Dichromated Gelatin (DCG) to make primary
harmonic holograms. The use of second harmonics in the visible region of the spectrum yields
high efficiency Lippmann holograms with a single processing. The reconstruction wavelength can
be equal to or shorter than the construction wavelength and is easily controlled in this method.
Such units offer the benefits of high efficiency and controllable bandwidths for applications in the