Patent ID: 8797515

Claim:
A method for measuring, from an amount of phase change of an interference pattern generated by irradiating an object to be measured with light, an amount of deformation of the object, the method comprising: causing two laser beams to be incident on the object; detecting a first speckle interference pattern generated by an interference of scattering lights of the two laser beams; detecting a second speckle interference pattern generated by modulating an optical path length of at least one laser beam out of the two laser beams; obtaining a speckle interference fringe image having a carrier fringe calculated based on difference between the first and the second speckle interference patterns; obtaining a phase of the speckle interference fringe image including a phase corresponding to the deformation of the object and a phase of a spatial carrier fringe; unwrapping the phase of the speckle interference fringe image; and calculating an amount of deformation of the object based on phase information corrected by the phase unwrapping, wherein a method for the modulating an optical path length of the laser beam includes causing a plane parallel transparent plate, arranged on an optical path where either one of the two laser beams becomes diverging light and at a position where the plane parallel transparent plate transmits said either one of the two laser beams, to tilt relative to the optical path.