Efficient ESPI method to identify vibration characteristics of transparent films

Electronic speckle pattern interferometry (ESPI) has been frequently used to study vibration characteristics of engineering structures. However, efficient ESPI methods for identifying the vibration characteristics of transparent membranes are rarely reported. A convenient approach to determine the resonant frequencies and the vibration modes of transparent films is proposed. A quasi-common-path ESPI (QCP-ESPI) is developed to detect out-of-plane deformation and visualize vibrational modes of a vibrating transparent diaphragm. An amplitude-modulation-based method is proposed for quick and accurate determining resonance of oscillating objects during frequency scanning. Experimental performances demonstrate the feasibility and efficiency of the QCP-ESPI and amplitude-modulation-based methods for determining the resonant frequency and vibration modes of transparent objects.