Abstract: A method and apparatus for making measurements on light fringes such as are produced by interferometers or gratings wherein such measurements can include measurements of position and velocity of an object such as a step and repeat carriage or microscope stageThe fringe pattern is sensed with a linear array detector whose elements are repetitively time multiplexed. The resultant output signal is filtered, yielding an AC signal with a phase indicative of fringe position. Rapid, digital, submicron counting is made possible using a phase lock loop to control the multiplexor clock. The advantages of AC interferometry are realized without optical modulation.

Abstract: A method and apparatus for generating and detecting changes in interference patterns such as may be used to measure small displacements. A collimated beam is diffracted to produce a standing wavefront along a surface. The surface is coincident with the surface of a device which emits a signal in response to changes in the intensity of the wave front. In one embodiment, the diffracting means is a grating and the signal emitting means includes a beam splitter that generates an interference pattern responsive to the intensity of the wave front. In another embodiment, the signal emitting means is a membrane that emits a signal in response to changes in the wavefront. The apparatus and method can be used in applications which include measurement of displacement and measurement of force in which no displacement takes place.

Abstract: A test sample support assembly having its greatest utility in a length measuring device in a temperature controlled environment. The sample support assembly has a main support, a pair of insulating members and a sample support. In one embodiment of this invention the sample support is made of a substantially distortion-free material thereby precisely positioning the sample within the temperature controlled environment. In the other embodiment of this invention the sample support acts as the temperature controlling element. The sample support is adjustably mounted with respect to the main support. This adjustable feature permits corrective movement of the sample support to take place in order to compensate for the undesirable movement of the sample support.