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Transverse Voltages for High Frequency Phonon Generation

IP.com Disclosure Number: IPCOM000087808D
Original Publication Date: 1977-Mar-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Von Gutfeld, RJ: AUTHOR

Abstract

The mode-locked laser 10 in the drawing emits a laser beam 11 directed by rotating mirror 12 through focusing lens 13 onto a slant-angle deposited film 14 composed of a material which is vacuum-deposited on piezoelectric crystal 15 with a slant angle, such that, when it is heated, a transverse thermoelectric voltage along the interface between the slant angle film 14 and crystal 15 is generated. The thermoelectric voltage operates upon crystal 15 to generate acoustic waves in the crystal piezoelectrically. Data applied from the laser 11 is stored in crystal 15 and can be stored or read out of crystal 15 by microwave cavity 16 when it generates an appropriate storage pulse. This permits separate addressing of many channels when crystal 15 is used for information storage.

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Transverse Voltages for High Frequency Phonon Generation

The mode-locked laser 10 in the drawing emits a laser beam 11 directed by rotating mirror 12 through focusing lens 13 onto a slant-angle deposited film 14 composed of a material which is vacuum-deposited on piezoelectric crystal 15 with a slant angle, such that, when it is heated, a transverse thermoelectric voltage along the interface between the slant angle film 14 and crystal 15 is generated. The thermoelectric voltage operates upon crystal 15 to generate acoustic waves in the crystal piezoelectrically. Data applied from the laser 11 is stored in crystal 15 and can be stored or read out of crystal 15 by microwave cavity 16 when it generates an appropriate storage pulse. This permits separate addressing of many channels when crystal 15 is used for information storage.

In R. J. von Gutfeld, Appl. Phys. Let. 23 (1973) 206 it is shown that thermoelectric voltages in the plane of a slant-angle deposited metallic film can be generated by optical excitation. The theory of this effect has also been described in R. J. von Gutfeld and E. E. Tynan, Appl. Phys. Let. 26 (1975) 680. The voltage develops in a direction parallel to that of deposited microscopic metallic columns, when heat energy is projected onto the plane of the sample. It can readily be shown that for a fixed laser power the voltage, and hence the electric field generated in the plane, is inversely proportional to the diameter of the excitation source. Thus, very small spots of focused laser light can generate large local electric fields. For example, voltages of 5 mV were observed for an incident laser spot 5 microns in diameter, 0.25 W, incident on a Mo film evaporated at a 70 Degrees slant angle, 2000 Angstroms thick. This voltage is equivalent to a local field of 2 volts/cm.

In the drawing this thermoelectric voltage generates acoustic waves into the piezoelectric crystal for writing and reading information in the acoustic echo storage technique described in N.
S. Shiren et al, Phys. Rev. Let. 31 (1973) 819. The mode-locked laser shown is used to generate short, high intensity laser pulses.

The laser is run continuously. When information is to be stored/read, a picosecond pulse from the mode-locked train is gated onto the metallic film to create the electric field which propagates in the piezoelectric crystal. The laser beam can be focused to a diameter on the order of the wavelength of the light being used. With a suitable deflection scheme thousands of individual spots can be addressed on the crystal face (typically on the order of 1 cm in diameter). The effect of the laser pulse and the resulting electric film is to launch an acoustic wave with frequency components, F, proportional to
F(Omega) = sin Omega Tau/2 over Omega where Tau is the width of the applied laser pulse and Omega the angular frequ...