Abstract-Terahertz transmission ellipsometry of vertically aligned multi-walled carbon nanotubes

http://apl.aip.org/resource/1/applab/v101/i11/p111107_s1?isAuthorized=no

M. J. Paul¹, N. A. Kuhta¹, J. L. Tomaino¹, A. D. Jameson¹, L. P. Maizy¹, T. Sharf¹, N. L. Rupesinghe², K. B. K. Teo², S. Inampudi³, V. A. Podolskiy³, E. D. Minot¹, and Yun-Shik Lee¹

¹Department of Physics, Oregon State University, Corvallis, Oregon 97331-6507, USA
²AIXTRON Ltd., Buckingway Business Park, Anderson Road, Swavesey, Cambridge CB24 4FQ, United Kingdom
³Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854, USA 

We demonstrate time-resolved terahertz transmission ellipsometry of vertically aligned multi-walled carbon nanotubes. The angle-resolved transmission measurements reveal anisotropic characteristics of the terahertz electrodynamics in multi-walled carbon nanotubes. The anisotropy is, however, unexpectedly weak: the ratio of the tube-axis conductivity to the transverse conductivity, σ_z/σ_xy ≅ 2.3, is nearly constant over the broad spectral range of 0.4–1.6 THz. The relatively weak anisotropy and the strong transverse electrical conduction indicate that THz fields readily induce electron transport between adjacent shells within multi-walled carbon nanotubes.

© 2012 American Institute of Physics

Abstract-Terahertz Excitation of a Coherent Λ-Type Three-Level System of Exciton-Polariton Modes in a Quantum-Well Microcavity

J. L. Tomaino¹, A. D. Jameson¹, Yun-Shik Lee^1,*, G. Khitrova², H. M. Gibbs², A. C. Klettke³, M. Kira³, and S. W. Koch^3 
1Department of Physics, Oregon State University, Corvallis, Oregon 97331, USA
²Optical Sciences Center, University of Arizona, Tucson, Arizona 85721, USA
³Department of Physics and Material Sciences Center, Philipps-University, 35032 Marburg, Germany

http://prl.aps.org/abstract/PRL/v108/i26/e267402

Interactions of few-cycle terahertz pulses with the induced optical polarization in a quantum-well microcavity reveal that the lower and higher exciton-polariton modes together with the optically forbidden 2p-exciton state form a unique Λ-type three-level system. Pronounced nonlinearities are observed via time-resolved strong-terahertz and weak-optical excitation spectroscopy and explained with a fully microscopic theory. The results show that the terahertz pulses strongly couple the exciton-polariton states to the 2p-exciton state while no resonant transition between the two polariton levels is observed.

© 2012 American Physical Society

URL:

http://link.aps.org/doi/10.1103/PhysRevLett.108.267402

DOI:

10.1103/PhysRevLett.108.267402

PACS:

78.67.De, 42.55.Sa, 71.35.Cc, 78.47.jb