Abstract: A surface to be inspected is step-scanned in multiple steps. In each step, the phase corresponding to a shape measurement region in an interference fringe pattern, and the wavelength of light are measured. After defining a distance between any point on the surface to be inspected and the center of curvature of a reference spherical surface as a function of wavenumber (integer) including the measured phase and wavelength as parameters, the wavenumber in each step is calculated from the relationship of the function between adjacent steps, and the moving distance between each step is calculated. A measurement value of the distance is calculated from the wavenumber and the function thereof, a design value of the distance is calculated using the calculated moving distance, and the shape error of the surface to be inspected is calculated from the difference between the measurement value and the design value.

Abstract: A surface to be inspected is step-scanned in multiple steps. In each step, the phase corresponding to a shape measurement region in an interference fringe pattern, and the wavelength of light are measured. After defining a distance between any point on the surface to be inspected and the center of curvature of a reference spherical surface as a function of wavenumber (integer) including the measured phase and wavelength as parameters, the wavenumber in each step is calculated from the relationship of the function between adjacent steps, and the moving distance between each step is calculated. A measurement value of the distance is calculated from the wavenumber and the function thereof, a design value of the distance is calculated using the calculated moving distance, and the shape error of the surface to be inspected is calculated from the difference between the measurement value and the design value.