Fringe localization control in holographic interferometry.

The practical use of holographic interferometry in nondestructive testing leads to many situations in which the characteristics of the fringe patterns make the observation and subsequent interpretation of the fringes difficult. Fringe control may then be employed to correct the troublesome parameters, the most commonly treated of which is fringe spacing. To gain more powerful control, a novel method is presented here that also permits one to change the localization of the fringe pattern. General vectorial expressions are derived that relate a tilt in the reference beam to a change in the fringe localization. Moreover the changes introduced into the fringe vector by this tilt can be suppressed by an adequate shift of the illumination beam focus. Some illustrative examples for a plane object are presented.