Double-exposure holographic interferometry

The technique employed is similar to that used to produce a conventional hologram (simple exposure). Let's assume we've made the holography setup shown in figure 1 a. A first exposure is made, with the pressure inside the thruster being p ₁ (state 1). The internal pressure is then raised from p ₁ to p ₂ , without touching anything else. A second pose is then carried out to register the thruster in state 2 (pressure p ₂ ).

After photographic...