22 research outputs found
Midinfrared third-harmonic generation from macroscopically aligned ultralong single-wall carbon nanotubes
We report the observation of strong third-harmonic generation from a macroscopic array of aligned
ultralong single-wall carbon nanotubes (SWCNTs)with intensemidinfrared radiation. Through power-dependent
experiments, we determined the absolute value of the third-order nonlinear optical susceptibility !(3) of our
SWCNT film to be 5.53 × 10−12 esu, three orders of magnitude larger than that of the fused silica reference we
used. Taking account of the filling factor of 8.75% for our SWCNT film, we estimate a !(3) of 6.32 × 10−11 esu
for a fully dense film. Furthermore, through polarization-dependent experiments, we extracted all the nonzero
elements of the !(3) tensor, determining the magnitude of the weaker tensor elements to be #1/6 of that of the
dominant !(3)
zzzz component
Ultrafast Optical Spectroscopy of Micelle-Suspended Single-Walled Carbon Nanotubes
We present results of wavelength-dependent ultrafast pump-probe experiments
on micelle-suspended single-walled carbon nanotubes. The linear absorption and
photoluminescence spectra of the samples show a number of chirality-dependent
peaks, and consequently, the pump-probe results sensitively depend on the
wavelength. In the wavelength range corresponding to the second van Hove
singularities (VHSs), we observe sub-picosecond decays, as has been seen in
previous pump-probe studies. We ascribe these ultrafast decays to intraband
carrier relaxation. On the other hand, in the wavelength range corresponding to
the first VHSs, we observe two distinct regimes in ultrafast carrier
relaxation: fast (0.3-1.2 ps) and slow (5-20 ps). The slow component, which has
not been observed previously, is resonantly enhanced whenever the pump photon
energy resonates with an interband absorption peak, and we attribute it to
radiative carrier recombination. Finally, the slow component is dependent on
the pH of the solution, which suggests an important role played by H ions
surrounding the nanotubes.Comment: 6 pages, 8 figures, changed title, revised, to be published in
Applied Physics