Nonlocal-response diffusion model of holographic recording in photopolymer

The standard one-dimensional diffusion equation is extended to include nonl ocal temporal and spatial medium responses. How such nonlocal effects arise in a photopolymer is discussed. It is argued that assuming rapid polymer c hain growth, any nonlocal temporal response can be dealt with so that the r esponse can be completely understood in terms of a steady-state nonlocal sp atial response. The resulting nonlocal diffusion equation is then solved nu merically, in low-harmonic approximation, to describe grating formation. Th e effects of the diffusion rate, the rate of polymerization, and a new para meter, the nonlocal response length, are examined by using the predictions of the model. By applying the two-wave coupled-wave model, assuming a linea r relationship between polymerized concentration and index modulation, the resulting variation of the grating diffraction efficiency is examined. (C) 2000 Optical Society of America [S0740-3232(00)02106-2].