Phys. Rev. Lett. 90, 055508 (2003) [4 pages]Infrared-Phonon–Polariton Resonance of the Nonlinear Susceptibility in GaAsReceived 2 October 2002; published 7 February 2003 Nonlinear probing of the fundamental lattice vibration of polar crystals is shown to reveal insight into higher-order cohesive lattice forces. With a free-electron laser tunable in the far infrared we experimentally investigate the dispersion of the second-order susceptibility due to the phonon resonance in GaAs. We observe a strong resonance enhancement of second harmonic light generation at half the optical phonon frequency, and in addition a minimum at a higher frequency below the phonon frequency. Measuring this frequency and comparison to a theoretical model allows the determination of competing higher-order lattice forces. © 2003 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.90.055508
DOI:
10.1103/PhysRevLett.90.055508
PACS:
63.20.Ry, 42.65.An, 42.65.Ky, 78.20.–e
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