INTERFERENCE FRINGE ANALYZING METHOD FOR SURFACE SHAPE MEASUREMENT AND THICKNESS UNUNIFORMITY MEASUREMENT OF TRANSPARENT PARALLEL FLAT PLATE

摘要

PROBLEM TO BE SOLVED: To resolve the problem of a conventional method measuring an optical thickness and a surface shape of a transparent parallel flat plate by a Twyman-Green interferometer where measurement error was large.;SOLUTION: A beam from an illumination light source with a temporally changing center wavelength λ is used as a parallel beam and it is guided onto a reference plane and a surface of the flat plate to be measured. The ratio of a distance L between the reference plane and the flat plate surface on an optical axis and the optical thickness nT of the flat plate is set at L=nT/3, and interference fringe information acquired from light interference of beams from the flat plate surface and rear face is picked up. At this point, 19 images are continuously picked up every time a phase difference of reflected beams from both faces changes by π/6. Phase information ψ₂(x, y) regarding ununiformity of the optical thickness of the flat plate is determined by applying an arithmetic process based upon an equation 1 using an equation 2 to the acquired 19 pieces of interference fringe image information I_-9(x, y), etc., I₉(x, y). The thickness ununiformity is measured by the proposed equation. In the same way, a height of the rear face is measured by another equation.;COPYRIGHT: (C)2003,JPO