a method of depositing the layers of an optical recording medium to their requisite thicknesses is disclosed in which optical monitoring of the reflectivity of a first dielectric layer during deposition is used to determine the deposition rate . the reflectivity is monitored to determine the time period in which the reflectivity reaches a maximum or minimum value , which occurs when the layer is a quarter wave thick . the deposition rate is derived from that time period , and the deposition is continued for a time in accordance with the deposition rate until the requisite thickness of the first dielectric layer is obtained . the second dielectric layer is deposited for a lesser time period in accordance with the deposition rate which has been optically derived during deposition of the first dielectric layer .