Abstract
We investigate the low-frequency dielectric response of the ferroelectrics LiNbO3 and LiTaO3 via the impulsive excitation and phase-sensitive detection of coherent phonon polaritons. Phonon polaritons are mixed light-polarization states that arise from the coupling of far-infrared light with phonon resonances and can be used to investigate these resonances. For ferroelectric crystals there are often more optical-phonon resonances observed than there are normal vibrations in the unit cell.1,2 The additional resonances are usually explained from the anharmonic coupling of different optical phonons (difference bands, combination bands).1,2 However, it was shown recently that the additional resonances can also result from transitions in the microscopic anharmonic potential of the phonon itself.3,4
© 1995 Optical Society of America
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