SU172085A1 - INTERFERENCE METHOD FOR CONTROLLING THE THICKNESS OF TRANSPARENT LAYERS - Google Patents

Description

An interference method for controlling the thickness of transparent layers formed on spherical and aspherical surfaces of optical components is known, in which the layer is illuminated with monochromatic light from the center of curvature of the surface, and the interference pattern obtained is measured by an optical microscope head with a rotating mechanism. However, the control by this method in the case of a significant angle between the normal to the surface at the edge of the part and the optical axis is difficult, since the aperture of the measuring microscope may be insufficient and interference fringes will not be observed with the microscope. Creating special turning devices for a microscope or part complicates the installation and reduces the measurement accuracy. The proposed interference method of controlling the thickness of transparent layers formed on surfaces of relatively large curvature differs from TeiM, that the layer is illuminated from the actual optical focus of the given surface. This method of illuminating the transparent layer makes it possible to obtain interfering beams, making small angles with the optical axis of the surface. A microscope with two relative movements — along the optical axis of the microscope and perpendicular to it — is used to measure the interference pattern. In addition, in order to simplify the design of the microscope, an optical head with a rotating mechanism has been removed from it. g FIG. 1 shows a schematic diagram, an installation for controlling the thickness of a transparent layer on a concave surface of relatively large curvature; in fig. 2 - the same for the convex surface of the optical part. The optical component / monitored layer 2 is illuminated with a monochromatic light source 3 from the actual optical focus of the surface. The interfering beams of rays reflected from the surfaces of the layer and the part will make small angles with the optical axis, and the interference pattern can be observed on any part of the part through a microscope 4 whose axis is parallel to the optical axis of the part. Knowing from the preliminary calculation the theoretical position of the interference fringes over the surface zones and the size of each interval between them, it is possible to measure the displacement of the corresponding interference fringes on the monitored layer using a measuring microscope and determine the deviation of the actual layer thickness from the required one. In the apparatus for controlling the thickness of the transparent layer on the convex surface of the part, the source 5 of monochromatic light is combined with the actual optical focus of the reflective optical part 6. The interference pattern appearing in the transparent layer 7 can be observed with a microscope 8 through the glass layer of the optical part. In this case, it is necessary to introduce a correction to the position of the interference band defined by the segment y, based on the position of the microscope determined by the segment y.

In each particular case, one can find one or another way of illuminating the layer from the actual optical focus of the surface, for example, using a light guide, a high-aperture condenser, etc.

The method can be used for contol, transparent layers with uneven thickness over the zones of the part during aspherization using a vacuum method, etc.

Subject invention

An interference method of controlling the thickness of transparent layers formed on spherical and aspherical surfaces of optical components, characterized in that, in order to increase the measurement accuracy by

excluding rotating devices for a measuring microscope or part, lighting the layer is made from the actual optical focus of this surface, and measuring the resulting interference pattern with a microscope with relative movements of it and this surface along the optical axis of the microscope and perpendicular to it.