Measurement of inner surface profile of a tube using two wavelength phase-shifting digital holography

A digital holographic method for evaluation of an inner surface profile of tubes is proposed. For surface contouring, two wavelength method using an injection-current induced wavelength change of a laser diode is used. To obtain the inner surface profile, a cone-shaped mirror is inserted into the tube. Distribution of an optical path length in the experimental alignment is calculated and utilized to compensate for a distortion occurring in the experimental profile of the surface due to a deviation of a mirror position. The shape of two seals pasted on the inner surface can be evaluated by the method with a digital image processing. It is shown that the proposed method can visualize and detect three dimensional shape of defects on the inner surface of tubes.