Photopolymers are organic materials that polymerize when illuminated with a suitable wavelength of light. They have many potential applications, such as optically written waveguides for 3D photonic circuits. Perhaps the most exciting applications are in the area of data storage. Holographic data storage has been identified as a significant goal, and photopolymers are the medium of choice for the digital versatile disc (DVD)-sized devices with terabyte-plus data densities promised by these 3D optical storage techniques. High-density magnetic tapes can currently hold∼500GB (approximately 200 million pages of text). Magnetic tape libraries, sold to governments and large companies, are made by connecting cabinets that hold ∼5,000 tapes. Companies like StorageTech sell over 22,000 of these cabinets annually, so the need for high-volume storage exists. Several important technical milestones have recently been achieved in this area, such as InPhase Technologies launching their holographic disc-drive in 2008. The commercial possibilities may explain why several companies, including Bayer, DuPont, General Electric, and Sony have entered this research area. Since 2000,1 our group has been developing detailed electromagnetic and material models to describe the operation of photopolymers.2–5 The aim has been to develop simulations4 that characterize the physical and chemical effects taking place within the material during and after exposure. These efforts could allow scientists to optimize materials and simulate their applications. Figure 1 shows the material processes involved. Exposing light produces a sinusoidal interference pattern. The grating causes diffraction of the probing beam in the non-latent material. Polymerization (initiated in the bright regions of the material layer) removes the monomer, producing a concentration gradient. The monomer diffuses from the dark to the bright regions. Non-local growth of the polymer chains (away from the point of Figure 1. Material processes occurring in photopolymers during and after exposure