Abstract: Optical membranes having embossed data on their surfaces are made by dispensing the polymer/solvent mixture onto a rotatable supporting surface bearing the embossed data, spinning the rotatable surface under conditions sufficient to form the membrane from the polymer and removing the membrane, after formation, from the rotatable surface. Such membranes can be light-transmissive, light-reflective or, as desired, partially reflective and partially transmissive.

Abstract: Edge-supported and fully supported membranes having substantially uniform thickness, and substantially parallel surfaces, and having the capacity to transmit at least about 90% of incident light with very little diffraction, dispersion or absorption of incident light are made by forming a polymer/solvent mixture, spin-coating a film of the polymer from the mixture onto a rotatable surface, which may have a release agent thereon, and, where a release agent is present, joining a frame or other support to the membrane and removing the membrane with its attached support from the surface. Apparatus for making such membranes includes a dispenser for dispensing a polymer/solvent mixture onto a rotatable support; a device for spinning the rotatable support at gradually increasing speeds from a first to a second speed; and a device for maintaining the speed of rotation of the support at the second speed until the membrane forms.

Abstract: A method for measuring accurately the optical thickness and index of refraction of thin, optical membranes includes directing light onto the membrane at one or more known angles of incidence, finding at least one angle of incidence, called a null angle, where the membrane reflects substantially none of the incident light, then calculating the optical thickness of the membrane, its index of refraction, or both, from one or more such null angles. Apparatus for this purpose includes means for directing a light beam onto thin, optical membranes, means for varying the angle of incidence of a light beam upon the membrane, and means for detecting the angles of incidence of the light beam on the membrane, including the null angles.