| 摘要 |
PURPOSE:To measure the shape of a wave front with high accuracy, on the basis of the subtraction data obtained by subtracting the reference data obtained by applying Fourier transform processing to the reference interference fringe data from a shearing interferometer from the data to be inspected due to an object to be measured. CONSTITUTION:The incidence of the fronts of the reflected waves due to both of a surface 8 to be inspected and a plane mirror 4 is performed by the opening and closing of shutters 3, 6 and the parallel beam passing through a half mirror 5 is incident to a shearing interferometer to be divided into two beams by a half mirror 9. One of the beams receives lateral shift by a parallel flat plate 13 having the angle phiof inclination to the beam so as to become preset shearing quantity and is reflected by a mirror 11 to reach a mirror 2. The other beam is reflected by a mirror 10 inclined by an angle theta to reach the mirror 12 and the shearing interference fringe corresponding to the angle theta is generated from two beams superposed each other on the mirror 12. This interference fringe is taken in a memory 16 by an area sensor 15 and subjected to Fourier transform processing to obtain reference data. Next, the reference data is subtracted from the data from the surface 18 to be inspected as correction data by an operation means 17 and the shape of a wave front can be measured with good accuracy.
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