Computerized tomography technique for reconstruction of obstructed phase data in shearography

Area of Science:

• Optical Metrology
• Interferometry
• Nondestructive Testing

Background:

• Shearography is an interferometric technique simplifying holographic setups and improving environmental stability.
• Its industrial acceptance is high, especially for nondestructive testing (NDT).
• A key limitation is its inapplicability to obstructed or inaccessible measurement areas.

Purpose of the Study:

• To develop a method for reconstructing phase distribution in obstructed areas using shearography.
• To overcome the limitation of optical accessibility in full-field optical measurement techniques.
• To enable NDT of complex geometries where direct imaging is impossible.

Main Methods:

• An algorithm based on the principles of tomography is presented.
• Imaginary rays are projected across the obstructed area from multiple directions.
• Linear equations are established by integrating phase directional derivatives along these rays, relating internal phase to boundary measurements.

Main Results:

• The algorithm successfully reconstructs the unavailable phase distribution in obstructed areas.
• It calculates the unknown phase distribution in blind areas from measured boundary phase data.
• Demonstrated applicability to shearography, with potential for other optical techniques.

Conclusions:

• The tomographic algorithm effectively reconstructs phase information in obstructed regions for shearography.
• This method significantly expands the applicability of shearography and similar optical techniques.
• It offers a viable solution for NDT of components with inaccessible measurement zones.