The optical properties (the reflectance and the absorption) of the systems thin metal film - thick lithium niobate substrate (with film thicknesses of 15, 20, 30 and 40 nm) implanted by Ar+ ions with energies of 50, 100 and 150 keV and doses of 1015 - 1016 cm-2 are investigated in the wide spectral range (λ = 0.2 - 15 μm). It is shown that ion implantation influence on the absorption and the reflectance of such systems. Intensive atoms intermixing on the interface “film - substrate” change the optical properties of such systems. Different materials result to different effects. The changes of surface structure of Ni and Mo film on lithium niobate substrate slowly influence on their optical properties. But Pd film on lithium niobate substrate result to independence of reflectance from wavelength in the wide spectral range with magnification of an adhesion of the film to the substrate. AFM investigations of such systems show changes of the surface structure of the samples after the implantation. The effective use of such materials for pyroelectric photodetectors is proposed. The characteristics of pyroelectric photodetectors on the base of the systems “thin metal (Ni, Mo, Pd) film - thick lithium niobate substrate” implanted by Ar+ ions were investigated and compared with similar photodetectors. Such photodetectors have high sensitivity, response, radiation stability, detectivity, large dynamic range. Their functional characteristics not worse that characteristics of similar photodetectors. Owing to high radiation stability (large adhesion of metal film to substrate) such metal film based pyroelectric photodetectors can effectively use for registration of power laser radiation. The production process of metal film based pyroelectric photodetectors implanted by Ar+ ions is also proposed.