Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Y. S. Lim, J. G. Ahn, T. Joo, K. J. Yee, E. H. Haroz, L. G. Booshehri, and J. Kono, "Coherent Lattice Vibrations in Small Diameter Single-Walled Carbon Nanotubes," in Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, OSA Technical Digest (CD) (Optica Publishing Group, 2009), paper IWD6. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article
We report on polarization-dependent transient carrier dynamics and coherent phonon oscillations in single-walled carbon nanotubes by determining the relation between the nanotube axis and the incident light polarization. Due to the anisotropic shape of nanotubes, optical absorption strongly depends on the polarization direction. We observed three decay components when the excitation wavelength was resonant with the E22 transition energy and observed two-decay components under off-resonance conditions. The transient absorption and coherent phonon amplitudes were measured as a function of the angle between the pump and probe polarizations and were analyzed based on the absorption anisotropy of carbon nanotubes.
We have observed large-amplitude coherent phonon oscillations of radial breathing modes (RBMs) in single-walled carbon nanotubes excited through the lowest-energy (E11) interband transitions. In contrast to the previously-studied coherent phonons excited through higher-energy (E22) transitions, these RBMs show comparable intensities between (n-m) mod 3 = 1 and -1 nanotubes. We also find novel non-resonantly excited RBMs over an excitation range of ~300 meV above the E11 transition, which we attribute to multi-phonon replicas arising from strong exciton-phonon coupling.
Using ultrahigh magnetic fields up to 170 T and polarized midinfrared radiation with tunable wavelengths from 9.22 to 10.67 $\ensuremath{\mu}$m, we studied cyclotron resonance in large-area graphene grown by chemical vapor deposition. Circular polarization dependent studies reveal strong $p$-type doping for as-grown graphene, and the dependence of the cyclotron resonance on radiation wavelength allows for a determination of the Fermi energy. Thermal annealing shifts the Fermi energy to near the Dirac point, resulting in the simultaneous appearance of hole and electron cyclotron resonance in the magnetic quantum limit, even though the sample is still $p$-type, due to graphene's linear dispersion and unique Landau level structure. These high-field studies therefore allow for a clear identification of cyclotron resonance features in large-area, low-mobility graphene samples.
In recent years, terahertz radiation sources are increasingly being exploited in military and civil applications. However, only a few studies have so far been conducted to examine the biological effects associated with terahertz radiation. In this study, we evaluated the cellular response of mesenchymal mouse stem cells exposed to THz radiation. We apply low-power radiation from both a pulsed broad-band (centered at 10 THz) source and from a CW laser (2.52 THz) source. Modeling, empirical characterization, and monitoring techniques were applied to minimize the impact of radiation-induced increases in temperature. qRT-PCR was used to evaluate changes in the transcriptional activity of selected hyperthermic genes. We found that temperature increases were minimal, and that the differential expression of the investigated heat shock proteins (HSP105, HSP90, and CPR) was unaffected, while the expression of certain other genes (Adiponectin, GLUT4, and PPARG) showed clear effects of the THz irradiation after prolonged, broad-band exposure.
We have studied the coherent dynamics of optical phonons in single-walled carbon nanotubes through impulsive stimulated Stokes and anti-Stokes Raman scattering. The probe energy dependence of phonon amplitude as well as preferential occurrence between Stokes and anti-Stokes components in response to chirped-pulse excitation are well explained within our model. The temperature dependence of the observed dephasing rate clearly exhibits a thermally-activated component, with an activation energy that coincides with the frequency of the radial breathing mode (RBM). This fact provides a clear picture for the dephasing of optical phonons by random frequency modulation via interaction with the RBM through anharmonicity. PACS numbers: 78.67.Ch, 61.48.De, 63.22.Gh, 81.07.De
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