Implementation of hologram interferometry with a continuously scanning reconstruction beam.

A system for fringe evaluation in hologram interferometry is studied in which a conjugate reconstruction beam scans the hologram, and the resulting fringe motion is observed in the real image of the object. The principle is suitable for semiautomatic evaluation. An earlier article presented a detailed theoretical analysis of the measuring principle, and the present paper deals with the practical aspects. It is shown that the system is capable of interpolating fringes to 1/100 of a fringe, which is experimentally verified by the determination of 3-D displacement components with an accuracy of about 40 nm and of strain with an accuracy of about 10 microstrain over an observation length of 1 cm. An analysis of the different error sources shows that the mechanical measures of the recording and evaluation setup have to be known to a small fraction of a millimeter.