Real-time holographic image restoration in azo dye doped polymer films

We describe a method that allows increasing the intensity of images holographically recorded in azo dye doped polymer films. The saturation of photoisomerization processes decreases the modulation depth of a holographic grating, hence the intensity of the reconstructed image. This process can be inhibited by illuminating a hologram with a uniform control beam that has the effect of increasing the saturation intensity of the film. Experiments done with a hologram recorded at 514 nm have shown that a control beam at 633 nm can increase the diffraction efficiency of the hologram, thus, allowing to restore the image at an intensity level facilitating its detection.