Source modulation for phase shifting in static and dynamic speckle shearing interferometry

摘要

Direct injection-current modulation of a diode laser source is demonstrated for phase-stepping, heterodyning and stroboscopic illumination in a shearing interferometer. The techniques are proposed as an alternative to the use of mechanical phase-shifters such as piezoelectric transducers, offering the advantages of ease of implementation, extended measurement bandwidth and elimination of active elements from the measurement head. The phase-stepping and heterodyning techniques require the interferometer to be unbalanced, which introduces an unwanted magnification mismatch into the shearing interferometer. A compensation technique using a block of high refractive-index material is described, and experimental demonstrations of each of the three techniques are presented.