Abstract
Digital holography allows production of high-speed three-dimensional images at rates over 100,000 frames per second; however, simultaneously obtaining suitable performance and levels of accuracy using digital holography is difficult. This problem prevents high-speed three-dimensional imaging from being used for vibrometry. In this paper, we propose and test a digital holography method that can produce vibration measurements. The method is based on single-shot phase-shifting interferometry. Herein, we imaged the surface of a loudspeaker diaphragm and measured its displacement due to the vibrations produced by a frequency sweep signal. We then analyzed the frequency of the experimental data and confirmed that the frequency spectra inferred from the reconstructed images agreed well with the spectra produced by the sound recorded by a microphone. This method can be used for measuring vibrations with three-dimensional imaging for loudspeakers, microelectromechanical systems, surface acoustic wave filters, and biological tissues and organs.
Highlights
High-speed and non-invasive imaging techniques are important for elucidating the size, shape, motion and function of biological tissues and organs[1,2,3,4,5,6,7,8,9,10]
Vibration displacements are smaller at high frequencies than at low frequencies; as a result, digital holography (DH) systems need to be very accurate in the direction of the depth of the DH to be used for high-speed 3D vibrometry
We generated the frequency-swept signal as a waveform audio format (WAV) file, and its frequencies were swept linearly from 0 to 20 kHz in 1.2 s
Summary
High-speed and non-invasive imaging techniques are important for elucidating the size, shape, motion and function of biological tissues and organs[1,2,3,4,5,6,7,8,9,10]. The 3D information of a recorded object can be reconstructed by adequately illuminating a hologram by using diffraction of light; in other words, holography can record and reconstruct the wavefronts of light, which include the light intensity and the phase distributions It is difficult for classical holography, which needs a holographic recording material to record a hologram, to reconstruct 3D motion pictures of fast phenomena, digital holography (DH)[15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38] can overcome the problem; this is because DH records holograms with an image sensor capable of capturing images in the form of a video, such as a charge-coupled device or complementary metal–oxide–semiconductor, instead of a holographic recording material that requires more time to rewrite itself as compared to an image sensor or can be exposed only once. We report the first experimental confirmation that high-speed 3D imaging can be used for vibrometry by parallel phase-shifting DH for the first time
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