Abstract: A system and technique for measuring the thickness of an optical element. A first energy signal of a first phase is transmitted into the element. The first signal reflects off of a distal surface of the element and is detected as a return signal. The phase of the reflected signal is compared to the phase of the transmitted signal and the frequency varied to extract a third signal representing a desired phase difference therebetween. Corresponding frequency data are processed to determine the thickness of the element at the point of transmission of the first signal.

Abstract: The present invention is directed to a new and improved active translation sensor which includes a first member having a fixed transmission grating, a second member having a movable linear array of light-emitting diodes disposed juxtaposition relationship with respect to one side of the fixed transmission grating, the second member being movable with respect to the other, electrical circuitry is being provided for successively applying electrical energy to each of the light-emitting diodes in a cyclical manner, a photodetector disposed on the other side of the fixed transmission on grating for detecting light transmitted through the grating, a phase detector for receiving a first signal corresponding to the phase of the circuitry for successively applying the electrical energy to the light-emitting diodes and second signal corresponding to the light detected by the photodetector and outputting a signal corresponding to the phase difference between the two signals, thereby indicating the relative linear positi

Abstract: An automatic focusing system for positioning silicon or other wafer within the focal plane of a photolithographic mask projection system. The position of the wafer is measured at a plurality of points and compared to the position of an optical flat located in the focal plane to provide signals for positioning the wafer at the focal plane of the projection system. The system also includes means for changing the contours of the wafer to cause it to lie in a known plane.