Holographic recording and hologram coherent self-enhancement (CSE) dependence on the intensity modulation (visibility), M , of the recording interference pattern is experimentally studied in order to determine the minimum possible modulation (modulation threshold) enabling recording or CSE. Such intensity modulation threshold can be caused by the inhomogeneity of the recording material. Elementary holograms – holographic gratings with 2µm period were recorded in an 12µm thick a-As2S3 film by 10 mW 532 nm YAG:Nd3+ laser light and read out at Bragg angle by a 633 nm He-Ne laser beam. In the M=1 case, the maximum diffraction efficiency ηmax=20% (with two beams) and the maximum CSE factor ξmax==11.8 have been found. The minimum modulation was found to be M=1.13×10-3 corresponding to ηmax=0.006% and ξmax=2.45. This minimum modulation was determined by the fact that diffracted light intensity reached the scattered light intensity background. Thus we have concluded that M threshold if it exists in a- As2S3 films is lower than M=1.13×10-3 . The obtained results can facilitate better CSE understanding (since CSE does not take place in all materials where efficient recording take place) and holographic recording optimization.