“…The differential equations provide a semi-analytical way of explaining why the index modulation is smaller when the separation between strips increases, that is to say, when low space frequencies are recorded. Subsequently, a lot of new models were presented, taking into account different aspects of the hologram formation process [12][13][14][15][16]. Some of the most interesting novelties were introduced by Sheridan and co-workers, specifically, introduction of the non-local polymerization concept and the high spatial frequency cut-off [14].…”