Fullfield time-resolved digital holographic interferometry : four-dimensional imaging of nanometer vibrations using stroboscopic illumination
Faculty of Sciences. Physics
OPTICAL MEASUREMENT TECHNIQUES FOR STRUCTURES & SYSTEMS2 (OPTIMESS2012)
5th International Conference on Optical Measurement Techniques for, Structures and Systems2 (OPTIMESS), APR 04-05, 2012, Antwerp, BELGIUM
, p. 103-110
University of Antwerp
In the past, interferometric holographic techniques have been used extensively to perform full-field, yet time-averaged analysis of vibrational patterns. When time-resolved information was needed, optical single-point measurement techniques, such as heterodyne interferometric vibrometry, were available. Recently, stroboscopically illuminated digital holography has been proven to yield both full-field and time-resolved information of vibrations with nanometer range amplitudes. In this technique, short laser pulses, synchronized to the vibration phase, are recorded. Good results have been achieved for high-frequency vibrations. However, due to the low energy in a single pulse, acquisition time increases for decreasing vibration frequency in order to receive enough energy on the camera, introducing problems such as artifacts due to slow movements of the object. In this work, stroboscopic holography is combined with a high power, frequency doubled pulsed Nd:YAG laser, which produces enough energy in a single pulse to perform single-shot holographic recordings. This new setup allows imaging vibrations ranging from quasi-static deformations to high-frequency vibrations (1 - 20000 Hz), while avoiding the earlier mentioned acquisition problems. The additional challenge is to synchronize the laser flash tube and Q-switch to the image acquisition and the vibration phase of the measured object. Results of measurements on a stretched circular latex membrane will be presented. The height displacement of the membrane is visualized over the entire surface as a function of time, thus providing true four-dimensional information. Extracting the vibration phase map is useful, for instance to reveal travelling waves, which are invisible on time averaged images.