Abstract: In-situ, nondestructive examination to test the efficacy of a riveted, bolted or bonded join of metal sheets, or to test whether a composite material is faulted, or to test whether a multi-layer patch is bonded properly, involves the creation of an interferometric hologram. A photographic film or plate is mounted closely above, and isolated vibrationally from a region of a structure containing the join, composite material or patch. The film or plate is illuminated by the expanded beam from a laser firstly when the structure is in a first state of stress, and secondly when the structure is in a second state of stress (the change in stress being sufficient to deform the region over which the film or plate is mounted). At each illumination, a diffraction pattern is produced in the emulsion of the plate or film by interference between the illuminating beam and that part of it which is reflected from the region. The two diffraction patterns combine to produce a fringe pattern in the emulsion.