Time differential phase detection method for robust industrial non-destructive inspections

A real-time and robust phase detection method for the in-line inspection of phase objects is proposed. Time differential phase detection (TDPD) detects phase signals by using four cameras within a short interval of time while moving an object across the beam path. Theory shows that the proposed method is substantially less susceptible to intensity deviation among multiple cameras and to spatial phase variation in both the object beam and reference beam when amplifying a weak signal by optical homodyne amplification. Experimental results show that stable phase retrieval is feasible in the presence of a non-uniform camera gain of up to 20% and a peal-to-valley wave aberration error in the optics of up to four wavelengths.