Detection of transient surface acoustic waves of nanometric amplitude with double-pulsed TV holography

Abstract

We describe the detection of bursts of surface acoustic waves by a double-pulsed TV holography technique. We describe mathematically the long- and short-wave bursts in the output correlograms and validate theoretical results with experimental images. The use of short-wave bursts permits us to scan the surface and makes it easier to distinguish, for purposes of nondestructive testing, the disturbances produced by flaws.

Video Ultrasonics by Pulsed TV Holography: A New Capability for Non-Destructive Testing of Shell Structures

“…Several authors have employed pulsed HI to visualize and even to extract quantitative data of instantaneous displacement fields of transient vibrations of mechanical components and of SAW (Gagosz 1974, 78-83;Vest 1979, 224-5 and 242-4;Pohl et al 1992;Fällströ m et al 1989;Henning and Mewes 1995). However, to the best of our knowledge, only our group has reported the detection of SAW by pulsed TVH (Cernadas et al 2002;Trillo et al 2003a;Cernadas et al 2006). Moreover, we developed a specific phase evaluation technique that renders quantitative data of transient SAW, namely the instantaneous out-of-plane acoustic displacement field and the out-of-plane acoustic displacement amplitude and phase fields, with a minimum measurable displacement of the order of one nanometer (Trillo et al 2003b).…”

“…At least one hologram is recorded for each mechanical state to be compared. However, there is no optical reconstruction of the recorded holograms; instead their intensity distribution is electronically processed to render the optical phase-difference map at the specimen surface, losing the three-dimensional character of HI and introducing extra noise due to the necessity to resolve the speckle in the recorded intensity distributions (Mast and Gordon 2001;Trillo et al 2003a;Trillo et al 2003b). The main advantages of TVH over HI are easier use, real-time display of results, and lower light power needed, being possible to maintain a refreshing cadence (limited by the camera and associated electronics) of tens of Hz with megapixel resolution and, not less important for its spreading in industrial applications, lower cost of the equipment.…”

Scanning ultrafast Sagnac interferometry for imaging two-dimensional surface wave propagation

“…Surface motion or strain-induced refractive index changes, in particular, provide suitable mechanisms for the optical sensing of surface acoustic waves ͑SAWs͒ on solids with visible optical wavelengths. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Developments in this field have been driven by the possibilities for nondestructively monitoring SAW propagation for the characterization of the elastic properties of isotropic and anisotropic materials, the mechanical properties of thin films, and SAW devices such as filters. [15][16][17][18][19][20] Moreover, the imaging of SAW propagation on crystals is of fundamental interest because of the complex focusing patterns that arise from the variation of sound velocity with propagation direction.…”

“…[15][16][17][18][19][20] Moreover, the imaging of SAW propagation on crystals is of fundamental interest because of the complex focusing patterns that arise from the variation of sound velocity with propagation direction. [1][2][3][4][5][6] Various optical detection techniques for SAW have been proposed: knife-edge techniques, [13][14][15] interferometric techniques, [4][5][6]17,18,21,22 holographic techniques, 7,8,[10][11][12]15 Schlieren techniques, 16 diffraction techniques, 19 and Brillouin scattering techniques. 15,23 Full information on the SAW field for a general broadband wave disturbance can be most simply obtained by real time detection, and the knife-edge and interferometric techniques have proved most successful for this.…”

Measurement of Lamb waves dispersion curves under narrowband monomode excitation using TV holography

“…We employed a double-pulsed TVH system that we have previously reported [6] and whose layout is depicted in Fig. 1.…”