Sandwich hologram interferometry. 2: some practical calculations.

Two hologram plates representing different object situations are bonded together with their emulsions separated. Fringes are formed that can be manipulated during reconstruction by moving the sandwich hologram in relation to the reconstruction beam. We have studied practical mathematical relations between sandwich motions, fringe changes, and object motion between the two exposures. Four dimensionless equations have been found that can be used for fringe evaluation by measuring sandwich motions. The wavelength of light is not involved in this new analogous compensating method. In contrast to ordinary double-exposed holograms, the sandwich hologram can directly reveal signs of displacements and maximal object strain.