Error factors of comparison in difference holographic interferometry

Difference holographic interferometry (DHI) is a holographic technique for direct optical comparative measurement of deformation, shape or refractive index distribution changes of two objects (master and test). At this procedure the test object is illuminated by reconstructed real images of the master object recorded previously. The holographic illumination is the spirit of the technique providing the unique possibility for direct optical comparison of the two objects. The differences in phases of the wave fronts belonging to the different states of the two objects lead to an interferogram that displays the difference of the measured quantities directly. The accurate comparison requires that the phases of the master and test object interference patterns should be compared at their corresponding points. There are two typical sources of error: (1) false reversing the master reference beams and (2)imperfect positioning of the test object. In the present paper a short summary of DHI is given, the above mentioned error sources are analyzed, techniques for minimizing their effects are suggested and the allowed shift of interference phase is estimated.