Simultaneous two-axis shearographic interferometer using multiple wavelengths and a color camera

• A shearography interferometer with simultaneous two-axis shearing is presented.
• Multi-wavelength light and a dichroic filter achieve the two-axis shearing.
• Extra wavelength available for absolute phase identification.
• Shearing errors are corrected mathematically.
• Surface slopes can be integrated to give the surface displacement map.

Multi-component measurements in shearography and other applications of Electronic Speckle Pattern Interferometry (ESPI) are typically achieved using multiple optical configurations that are activated sequentially to measure each desired quantity separately. A novel optical setup is introduced here where orthogonal shearography measurements are simultaneously made using a single color-camera imaging multiple monochromatic light sources of different wavelengths. The Red–Green–Blue (RGB) sensors of a conventional Bayer type camera are read separately, thereby providing three independent color signals and independent ESPI phase maps. Orthogonal axis shearography is achieved using a modified shearography interferometer where a dichroic filter is added to provide a second wavelength-dependent measurement. The availability of the two surface slopes gives the opportunity for the data to be summed numerically to give the surface displacement shape. This application is of significant practical interest because the surface displacement measurement can be made under field conditions by taking advantage of the well-known optical stability of shearography measurements. The two simultaneously measured surface slopes also offer the possibility to mathematically compensate for non-uniformity and non-orthogonality in the image shear caused by mirror non-flatness and/or mirror misalignments.