A 10 milliwatt HeNe laser is inadequate for all but the smallest holograms recorded in this material. Unfortunately, we have also found that the polymer does not respond well to extremely long exposures. It's dependence on monomer migration seems to require that a certain base energy flux be present to insure optimal efficiency. A higher energy laser, with a wavelength more in line with the polymer's peak sensitivity, is almost required. These new lasers are efficient and stable, capable of providing up to 5 Watts of power in air-cooled packages that plug into a standard 120 V outlet.
Coherence lengths can vary, from many meters to only millimeters, depending on the model.
These will provide a cheaper, but equally suitable alternative. We have exposed in photopolymer with both, with excellent results. Film handling Xylene and other odoriferous index-matching fluids are no longer required when making holograms in photopolymer, due to the material's inherent tackiness. In standard operations, the film is attached directly to the plateholder with a print-ink roller or the equivalent. A laminar-flow filtered air hood is helpful to prevent dust from being trapped on the film surface.