Apparatus and method for automatically focusing an interference microscope

摘要

Automatic focusing of an interference microscope is accomplished by directly sensing an interference pattern produced by a white light source with an auxiliary point detector. A beamsplitter intercepts part of the interference beam and directs it to the point detector. A narrow band filter filters light passing through the beam splitter on its way to a main detector array. A memory lock position of the microscope objective is manually selected and stored. Initially, the objective moves rapidly from the memory lock position until the presence of fringes is detected by the point detector. Momentum of the microscope causes the objective to overshoot beyond a fringe window. The microscope objective then is moved more slowly through the interference window until fringes again are detected; the lower speed results in substantially reduced overshoot. Intensity measurements from the point detector are sensed and stored as the objective moves through the width of the fringe window. The microscope objective then is yet more slowly moved through the fringe window while sensing the intensities produced by the point detector until the objective reaches a point at which the intensity is equal to a preselected percentage of the maximum stored intensity.