Disclosed is a method of producing a stator blade for use in a turbo-molecular pump. A battery cabinet or relay rack has provision for multiple tiers of batteries spaced so that batteries may be inserted in each tier. The horizontal fins have a swing shaft, respectively, and are disposed pivotally about the swing shaft within the retainer. A change in the amplitude and phase of the interference beams caused by the sample are obtained using a fringe scanning method, and a detector is used to detect the resulting image.