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Generator of Coherent Infrared Frequency Phonons

IP.com Disclosure Number: IPCOM000090390D
Original Publication Date: 1969-Apr-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Pomeranz, M: AUTHOR

Abstract

This device is for generating coherent acoustic waves or phonons of a frequency of the order of 10/12/ cycles/sec. Single crystal 2 is chosen so that a DC source 4 applies an electric field across such crystal via ohmic contacts 6 and 8. The choice of crystal is critical in that the material used requires it having an acoustic dispersion curve whose slope is negative at the frequency of the phonons to be generated. Such an acoustic dispersion curve is shown in drawing 2. The frequency omega of the acoustic wave is plotted as a function of k which equals 2 pi times the reciprocal of the wavelength lambda.

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Generator of Coherent Infrared Frequency Phonons

This device is for generating coherent acoustic waves or phonons of a frequency of the order of 10/12/ cycles/sec. Single crystal 2 is chosen so that a DC source 4 applies an electric field across such crystal via ohmic contacts 6 and 8. The choice of crystal is critical in that the material used requires it having an acoustic dispersion curve whose slope is negative at the frequency of the phonons to be generated. Such an acoustic dispersion curve is shown in drawing 2. The frequency omega of the acoustic wave is plotted as a function of k which equals 2 pi times the reciprocal of the wavelength lambda.

When an electric current is applied to crystal 2, such that the drift velocity of the electrons equals the phase velocity of the phonons for which a omega/ k<0, coherent phonons of the frequency omega are generated. The mechanism is similar to that of the backward-wave oscillator tube which generates electromagnetic waves at microwave frequencies. By varying the magnitude of the current going through crystal 2, the frequency of the phonons is variable. Thus, the device is voltage-tunable.

There are many materials where the ratio omega/k>0, but a omega/ak<0. Point A on the optical dispersion curve and point B on the acoustical dispersion curve meet the requirement that a omega/ak<0. Lead, iron, gallium arsenide and lead telluride are representative materials having these characteristics for particular modes of polar...