Influence of blue and red light illumination on the holographic storage in an azopolyester–PMMA blend

• Volume holographic gratings in azopolyester–PMMA blends depend on blue and red light irradiation.
• Cis isomers induced by blue irradiation seem to be necessary to record stable holographic gratings.
• The control of cis content by irradiation allows optimize recording and grating multiplexing.

Volume holographic polarization gratings have been stored in thick films of blends of a side-chain azobenzene polyester and a poly(methyl methacrylate) (PMMA) homopolymers. The azobenzene content in the blend is 0.2 wt%, and the holograms are recorded by using 2 ms 4 mJ/cm2 488 nm light pulses. The dependence of holographic storage on the recording condition has been studied. No stable gratings can be recorded in thermally quenched films. The presence of cis isomers that can be induced by blue light irradiation seems to be necessary to store stable gratings. The cis isomer content and consequently the grating efficiency can be changed by blue and red light irradiation. By choosing appropriate conditions stable and rewritable polarization gratings have been recorded. Up to 20 gratings with diffraction efficiency values higher than 5 × 10−5 have been multiplexed.