Multi-point vibrometer based on high-speed digital in-line holography

Abstract

This paper describes a digital holographic setup based on in-line holography and a high-speed recording to get a multipoint vibrometer. The use of a high-speed sensor leads to specificities that enable the in-line configuration to be used. The case of transient vibrations is investigated through a full simulation of the holographic process. The simulation shows that the first instants are critical since distortion may occur, resulting in errors in the phase measurement. Experimental results are provided by exciting an aluminum beam with a transient signal. A comparison with the velocity measured by a pointwise vibrometer is provided. Frequency response functions are extracted and the experimental results confirm the ability of the method to provide full-field contactless measurements at the high-speed time scale evolution of the vibration.

Lock-in Vibration Retrieval Based on High-speed Full-field Coherent Imaging

“…In the proposed approach, the specificity is that the spatial frequencies of R are set to {u 0 , v 0 } = {0, 0}, corresponding to the on-axis configuration. This point is discussed in 49 and the reader is invited to have a look at the paper for further details. The illuminated object surface is generally at distance d 0 from the recording sensor which is used without any imaging lens (arrangement known as the Fresnel configuration).…”

“…The reference wave is expanded, spatially filtered using a spatial filter (microscope objective and microscopic pinhole), and collimated to produce a smooth plane reference wave impacting the sensor at normal incidence. So, the set-up is arranged in the on-line configuration 49 .…”

“…Although providing quantitative data, the recording process required complex operations such as phase shifting and laser pulse triggering. More recently, the use of high-speed sensors permitted to acquire holographic data at the time-evolution of the studied phenomena 42,[44][45][46][47][48][49] . The advantage is that the optical assembly is considerably simplified as it does not require a pulsed laser, double pulse laser, or any generation of strobe light pulses.…”

“…In this paper, we report contact-less large field vibrometry with high-speed coherent imaging based on on-line digital holography, yielding full-field amplitude and phase vibration measurements. Whereas on-line digital holography suffers from the overlap of the diffraction order 49 , we discuss and apply a vibration retrieval algorithm that yield accurate measurements. The algorithm restores the operational deformation in terms of amplitude and phase of a structure submitted to harmonic excitation.…”

Time resolved digital holography applied to droplets fragmentation by shockwave

“…Both main principles and basic rules of high speed imaging have been extensively discussed in previous paper of the same research group 5 . In line digital holography 6 will be performed as it is robust to vibrations and allows high resolution reconstructions of small objects. The shock tube and the generated shockwave will be described as well as the camera performances used to grab the images sequence in high speed.…”