Phase-Coherent Light Scattering Method
We demonstrate here a new phase-coherent light scattering method. Spontaneous Brillouin scattering is caused by thermally excited phonons whose phases have no physical meaning because of their random, incoherent nature. However, coherent phonons having phase information can be generated resonantly by an optically induced scanning interference pattern, when the dispersion relation of phonons is satisfied. By a phase-sensitive detection of the light scattered by optically generated coherent phonons, we have succeeded in measuring complex resonance spectra of acoustic phonons, which we call complex Brillouin spectra, with an ultimate signal-to-noise ratio.
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