Two-step phase shifting for optical nondestructive testing

A novel method simplifies the process of interferometric computation while increasing speed and decreasing storage requirements. With the rapid development of high-quality CCDs and fast digital-image processing, phase-shifting interferometry (PSI) has emerged as a powerful means of optical noncontact and nondestructive testing. Combined with techniques such as holographic microscopy and 3D metrology, PSI is particularly well suited to evaluate wafers and optoelectronic devices. Classical interferometry provides information about an object by recording the fringe patterns generated by the interference of two illuminating laser beams. In PSI, a single laser beam is split into a ‘reference ’ beam and an ‘object ’ beam that are later recombined. Changing the phase angle of the reference beam stepwise during testing gives additional information that can be analyzed using appropriate algorithms. The attraction of PS