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Acoustic Frequency Selector for Optically Generated Acoustic Phonons

IP.com Disclosure Number: IPCOM000088753D
Original Publication Date: 1977-Jul-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Dreyfus, RW: AUTHOR [+2]

Abstract

Large amplitude acoustic waves can be generated by pulses of light if the boundary surface that absorbs the light is properly clamped by means of a thin film to produce stress waves. In many applications it is desirable to have a narrow band of acoustic frequencies. Generally, the methods so far described, using light as the source of the acoustic waves, produce a large range of frequencies determined by the frequency spectrum of the Fourier transform of the applied pulse plus several factors relating to the thermal response of the medium. For a square pulse of amplitude A of light in Fig. 1A of width t(o), incident on a constrained film, the spectrum of frequencies appearing as acoustic waves 14 can be estimated to a first approximation by the plot shown in Fig. 1B.

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Acoustic Frequency Selector for Optically Generated Acoustic Phonons

Large amplitude acoustic waves can be generated by pulses of light if the boundary surface that absorbs the light is properly clamped by means of a thin film to produce stress waves. In many applications it is desirable to have a narrow band of acoustic frequencies. Generally, the methods so far described, using light as the source of the acoustic waves, produce a large range of frequencies determined by the frequency spectrum of the Fourier transform of the applied pulse plus several factors relating to the thermal response of the medium. For a square pulse of amplitude A of light in Fig. 1A of width t(o), incident on a constrained film, the spectrum of frequencies appearing as acoustic waves 14 can be estimated to a first approximation by the plot shown in Fig. 1B.

This spectrum is limited to a much narrower bandwidth, typically required for most applications, which results also in an enhancement of the phonons' amplitude at the desired frequency by a structure shown in Fig. 2. Alternate layers of transparent material 10 and semitransparent material 11 are shown. The semitransparent material 11 is typically a thin metallic layer and serves to absorb some energy from intense light source 12. The thickness of layers 10 and 11 is adjusted to allow for uniform heating at each interface. Nonabsorbing layers 10 are made of a dielectric with a thickness equal to the desired acoustic wavelength lambda...