A hard and durable single-layer or multilayer artireflection coating for use with a high refractive-index IR transparent substrate is provided. The coating is prepared by concurrent deposition of TiO.sub.2 and MgF.sub.2 with the reactive ion-assistance on the IR transparent substrate within a single vacuum chamber. The refractive-index of this film is adjustable by varying the relative deposition rate of the two materials (i.e. controlling the ratio of the materials) to optimize the transmittance of the incident IR irradiation. The opitical thickness of each film of the single-layer and multilayer antireflection coatings is one-quarter wavelength of the IR irradiation.