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Optical Photoelastic Doppler Shifter

IP.com Disclosure Number: IPCOM000090212D
Original Publication Date: 1969-Mar-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Shiren, NS: AUTHOR

Abstract

This system is for shifting the frequency of a laser beam by periodically changing the index of refraction of a modulating medium using an acoustic wave.

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Optical Photoelastic Doppler Shifter

This system is for shifting the frequency of a laser beam by periodically changing the index of refraction of a modulating medium using an acoustic wave.

It is desired to shift the frequency of a light wave such as light beam 2, drawing A, emanating at a frequency f from pulsed laser source 4. Crystal 6 has transducer 8 fixed to it so that a radio-frequency wave from RF generator 10 can be applied to such transducer and cause an acoustical wave to traverse crystal
6. Lens 12 focuses unmodulated beam 2 so that its diameter within crystal 6 is less than one half the acoustic wavelength and lens 14 creates a parallel beam 16 of the modulated light. Where crystal 6 is piezoelectric, such as lithium niobate, then a transducer is not needed since lithium niobate directly converts electrical energy into acoustical energy.

Drawing B shows the relationship of a time-varying acoustical wave 18 in the crystal and the time-varying light beam 2 to be modulated by wave 18. Assuming either a travelling or standing acoustic wave, then when the unmodulated light pulse is symmetrically positioned in time about a positive or negative peak amplitude of the acoustic wave as a I, the maximum frequency modulation of the light pulse occurs. When the peak amplitude of the light pulse coincides with a zero amplitude position, as at 11, of the standing acoustic wave, then the frequency shift from the initial light frequency f to a new frequency is a max...