Full field displacement measurement by double symmetrical illumination with diode lasers through a pair of double exposure reflectionholograms

Compact and stable phase stepping interferometer for shape and full field displacement measurement in static and in “real time” operation mode is presented. Double symmetrical illumination of the object in two orthogonal planes with diode lasers, emitting in NIR (790 nm and 830 nm), through a four-exposure reflective holographic optical element (Denisiyk's volume reflection holograms of a reference plane) is applied. The proposed four channels one-beam interferometer is very compact, as the diode lasers without collimators and spatial filters are used directly for reconstruction of the reference planes from a pair of double exposure reflection holograms and for object's illumination through the same holographic optical element. Phase stepping is introduced simply by precise increments of the diode lasers current. By introduction of removable sinusoidal phase gratings and removal of the holographic optical element, the system operates as a single-shot fringe projection profilometer for shape measurement that is essential for precise estimation of displacement vector's components. The proposed system is very stable against external noise, produced by vibrations, temperature changes, air flows, as well as against the influence of object's “rigid body” motion, as the compact and low weight interferometer can be stably fixed directly onto the measured construction.

► Compact diode lasers system for full field displacement measurement is reported.
► Object's illumination is through pair double exposure reflection holograms.
► Reference planes for the four interferometers are reconstructed from the holograms.
► Analysis of experimentally obtained results is presented.