Spatial photoresponse, formfactor, and requirements to holographic materials

Problems arising when recording holograms in volume materials and manifesting themselves, firstly, as the spatial resonance of the hologram recording field with refractive index inhomogeneities caused by this recording are considered. Secondly, they manifest themselves as cross-coupling of two nonlinearities in the process of holographic recording–nonlinearity of the diffraction efficiency and nonlinearity of the distribution of the exposure and visibility recorded by the holographic grating over the hologram field. It is noted that the appearance of one more nonlinearity—the nonlinear photoresponse of the holographic material–leads not to a decrease in the diffraction efficiency but to an increase in it under certain conditions. In this work, main classes of volume holographic materials are distinguished–relaxation free dynamic media and media with development. Restrictions of the maximum achievable diffraction efficiency for both types of the media are demonstrated. Recommendations on elimination of undesirable consequences of the revealed effects are formulated. The recommendations are based on the analysis of main regularities in the formation of the photoresponse with allowance for the spatial resonance and presence of the formfactor.