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Excitation of Directed Surface Acoustic Pulses by an Optical Phased Array

IP.com Disclosure Number: IPCOM000044026D
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Tam, A: AUTHOR [+2]

Abstract

High-amplitude surface acoustic pulses (SAPs) are generated by the phase-matched application of light pulses through optical fibers with varying lengths. The properties of solid or liquid surfaces may be analyzed by measuring the propagation characteristics of SAPs. Accurate results require long measuring distances and thus high-amplitude pulses that are difficult to excite without surface damage or undesired non-linear effects. Therefore, it is proposed that the single-laser pulse, used for conventional SAP excitation, be replaced by a number of low-energy light pulses that are applied along a line at distances satisfying a phase-matched excitation. In the figure, exit beam 1 of a short pulse laser, such as an Nd:Yag laser (N500 mJ, 15 ns), is focussed by lens 2 onto the ends of a multitude of optical fibers 3a, 3b ...

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Excitation of Directed Surface Acoustic Pulses by an Optical Phased Array

High-amplitude surface acoustic pulses (SAPs) are generated by the phase- matched application of light pulses through optical fibers with varying lengths. The properties of solid or liquid surfaces may be analyzed by measuring the propagation characteristics of SAPs. Accurate results require long measuring distances and thus high-amplitude pulses that are difficult to excite without surface damage or undesired non-linear effects. Therefore, it is proposed that the single-laser pulse, used for conventional SAP excitation, be replaced by a number of low-energy light pulses that are applied along a line at distances satisfying a phase-matched excitation. In the figure, exit beam 1 of a short pulse laser, such as an Nd:Yag laser (N500 mJ, 15 ns), is focussed by lens 2 onto the ends of a multitude of optical fibers 3a, 3b ... of variable lengths. The other fiber ends are arranged along a line at a height of dN2 m above the surface 4 to be analyzed. The mutual spacing di between adjacent fiber ends is di = c x WT, where c is the acoustic pulse velocity and Wt is the time delay of the optical pulse in the longer one of the two fibers. For a typical value of c = 5 x 103 m/s and di = 10 m, the required delay of the optical pulse is 2 ns, corresponding to an additional fiber length of WL = 0.4 m. The SAP thus travels with increasing amplitude in the positive x-direction, eventually reaching acoustic...