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Producing Ultrasonic Waves Using Optical or Thermal Pulses

IP.com Disclosure Number: IPCOM000088173D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Melcher, R: AUTHOR [+2]

Abstract

Methods have been described for generating phonons (acoustic) resulting from the expansion and contraction of thin regions of material absorbing high density light (or other energies) pulses [1,2]. For optical absorption by an absorbing uniform solid half space (or rod) [1], or by a thin film deposited on such a rod [2,3], phonons are produced with frequencies proportional to the Fourier transform of the input optical waveform.

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Producing Ultrasonic Waves Using Optical or Thermal Pulses

Methods have been described for generating phonons (acoustic) resulting from the expansion and contraction of thin regions of material absorbing high density light (or other energies) pulses [1,2]. For optical absorption by an absorbing uniform solid half space (or rod) [1], or by a thin film deposited on such a rod [2,3], phonons are produced with frequencies proportional to the Fourier transform of the input optical waveform.

Phonons can be generated utilizing light or other energy pulses 11 absorbed by a medium 10 (Fig. 1) containing an oriented piezoelectric material in the form of a thin bulk slab or film such as degenerate GaAs. Medium 10 must have a fast dielectric relaxation time.) The mechanism giving rise to phonons which can be distinguished from that of [1-3] consists of the following: (1) The light (energy) pulse 11 incident on the front surface is absorbed and produces 2 transient temperature gradient normal to the plane of the piezoelectric medium. (2) The temperature gradient produces a transient thermoelectric voltage and hence an E field in the direction of the temperature gradient. (3) The piezoelectric tensor provides coupling between the transient E field and a stress in the medium. The stress launches acoustic waves whose frequencies are determined by the Fourier transform of the temporal input pulse. The mode (transverse or longitudinal) of propagation depends on the orientation of...