期刊
JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA
卷 115, 期 3, 页码 1142-1146出版社
ACOUSTICAL SOC AMER AMER INST PHYSICS
DOI: 10.1121/1.1643367
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The optoacoustic generation of a helicoidal ultrasonic beam is demonstrated. Such an ultrasonic doughnut beam has a pressure amplitude minimum in the center along its entire longitudinal extension, and it carries orbital angular momentum. It is produced by illuminating a specially structured absorbing surface in a water tank with pulsed laser light. The absorbing surface has a profile with a screw dislocation, similar to the transverse cross-sectional surface of a helix. Upon illumination with modulated light, a correspondingly prepared absorber generates an ultrasonic wave with the desired phase discontinuity in its wave front, which propagates through the water tank and is detected with spatial resolution using a scanning needle hydrophone. This situation can be viewed as the optoacoustic realization of a diffractive acoustical element. The method can be extended to tailor optoacoustically generated ultrasonic waves in a customized way. (C) 2004 Acoustical Society of America.
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