Biphotonic photochromic reaction results in an increase in the efficiency of the holographic recording process in an azo polymer.

Holographic grating recording in azobenzene-based polymers using a single coherent light of a specific wavelength (monophotonic recording) is the basis of the majority of the applications of this type of material. Here, we report a new approach to holographic recording that uses two light sources having different wavelengths during the recording process (biphotonic recording). The efficiency of the recording process was improved significantly compared to that of the monophotonic recording. The results, by presenting a simple way to increase the efficiency of the recording process, have important implications for the applications of azobenzene-based materials. They indicate how the performance of the already proposed devices can be improved, and they can open a new way to developing applications of this class of materials.