Investigation of the sensitivity to humidity of an acrylamide-based photopolymer containing N-phenylglycine as a photoinitiator

Sensitivity of holographic recording materials to the relative humidity (RH) of the environment often restricts their use in fabrication of holographic optical elements and other applications. It is important to develop materials with little or no sensitivity to humidity. In this paper the humidity response of transmission gratings recorded in an acrylamide-based photopolymer containing N-phenylglycine (NPG) as a photoinitiator is studied at RH = 20-90%. The hologram is found to be completely insensitive to humidity at RH below 70% and its diffraction efficiency remains constant. A decrease in diffraction efficiency is observed at RH = 80-90% but this decrease is fully reversible, demonstrating quantitatively the NPG photopolymer's excellent resistance to humidity.