[en] Up to the present time, perfect crystal interferometers of both two-crystal and three-crystal Laue-case variety have been used to explore the optical characteristics of neutrons of diffracting wavelength. In addition, very recently the classical optical experiments of the diffraction by an absorbing edge, by an absorbing wire and by single and double slit assemblies have been performed for cold neutrons. These experiments show with high precision the validity for matter waves of the standard Fresnel-Kirchhoff approach to diffraction