Ultrafast Phonon Decay in Complex Oxides

The decay of multiple Raman active vibrations has been directly traced, in time, in technologically important wide bandgap semiconduction oxides such as BaSnO3 (BSO), STiO3 (STO), and KTiOPO4 (KTP) crystal, which have important applications in laser frequency conversion. A time-domain coherent Raman technique, with excellent time (~120 fs) and spectral resolutions, has been applied to measure the ultrafast decay rates of optical phonons with 350–1500 cm−1 frequencies. Phonon decay mechanisms via phonon energy loss due to second- and third-order parametric processes have been discussed. The correspondingly high equivalent spectral resolution allowed for the determination of the phonon line bandwidths to be within 7.2–8.3 cm−1 (BSO), 8.5–9.7 cm−1 (STO), and 6.2–18.6 cm−1 (KTP).