Highly Stable Vibration Measurements by Common-path off-axis Digital Holography

Measurements of vibration and dynamic deformation with high resolution and accuracy by non-destructive techniques are of great interest in many branches of engineering. We report a non-destructive method based on digital holographic interferometry for high-precision micro-vibration measurement of a 3D object. Herein, a new and simple configuration of a common-path off-axis digital holographic system, with high mechanical stability and compact in size, is proposed. The simplicity, compactness, and high stability of the proposed setup are provided by employing a wedge plate in-line with the test object to create a clean reference beam. The object and reference beams propagate the same path, without the need for any specialized optical component or arrangement, and these beams allow to interfere on the faceplate of the image sensor to form a digital hologram. The feasibility of the proposed system is demonstrated by measuring the vibration of the objects driven by different excitation signals. A series of digital holograms of a vibrating object is recorded by the use of a high-speed image sensor. The result of the reconstruction of the recorded holograms is an array of complex numbers containing the complete amplitude and phase profile of the object, which in turn provides displacement and vibration information. Due to its simple geometry and significant outcomes, the proposed system could be established as a powerful tool for a wide range of optical imaging and measurement investigations.