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Y Ron Shen

Publications and source records attributed to Y Ron Shen.

5 recordsLinked to original sources
PubMed2006

General properties of local plasmons in metal nanostructures.

Under the quasistatic approximation, the characteristics of a local plasmon resonance of a metal nanostructure exhibit several general properties. The resonance frequency depends on the fraction of plasmon energy residing in the metal through the real dielectric function of the metal. For a given resonant frequency, the Q factor of the resonance is determined only by the complex dielectric function of the metal material, independent of the nanostructure form or the dielectric environment. A simple result describing the effect of optical gain on the Q factor is also obtained.

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PubMed2006

Ultrafast vibrational dynamics at water interfaces.

Time-resolved sum-frequency vibrational spectroscopy permits the study of hitherto neglected ultrafast vibrational dynamics of neat water interfaces. Measurements on interfacial bonded OH stretch modes revealed relaxation behavior on sub-picosecond time scales in close resemblance to that of bulk water. Vibrational excitation is followed by spectral diffusion, vibrational relaxation, and thermalization in the hydrogen-bonding network. Dephasing of the excitation occurs in </=100 femtoseconds. Population relaxation of the dangling OH stretch was found to have a time constant of 1.3 picoseconds, the same as that for excitation transfer between hydrogen-bonded and unbonded OH stretches of water molecules surrounded by acetone.

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PubMed2006

Electron dynamics of silicon surface states: second-harmonic hole burning on Si(111)-(7 x 7).

We report the first all-optical study of homogeneous linewidths of surface excitations by the spectral-hole-burning technique with surface-specific second-harmonic generation as a probe. Measurement of transient spectral holes induced by a 100 fs pump pulse in excitations of the surface dangling-bond states of Si(111)-(7 x 7) led to a pump-fluence-dependent homogeneous linewidth as broad as approximately 100 meV or a dephasing time as short as 15 fs. The hole-burning spectra also revealed a strong coupling between the localized dangling-bond states and the associated surface phonon mode at 570 cm(-1). Carrier-carrier scattering was responsible for the linear dependence of the dephasing rate on pump fluence, and the carrier screening effect appeared to be weak.

Journal Article↗
PubMed2006

Stimulated terahertz emission from intraexcitonic transitions in Cu2O.

We report the first observation of stimulated emission of terahertz radiation from internal transitions of excitons. The far-infrared electromagnetic response of Cu2O is monitored via broadband terahertz pulses after ultrafast resonant excitation of three-dimensional 3p excitons. Stimulated emission from the 3p to the energetically lower 2s bound level occurs at a photon energy of 6.6 meV, with a cross section of approximately 10(-14) cm2. Simultaneous excitation of both exciton levels, in turn, drives quantum beats, which lead to efficient terahertz emission sharply peaked at the difference frequency.

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