Coherent monochromatic phonons in highly-purified semiconducting single-wall carbon nanotubes

TL;DR

This study investigates how polarized femtosecond laser pulses excite coherent phonons in purified semiconducting carbon nanotubes, revealing polarization-dependent excitation mechanisms linked to resonant conditions.

Contribution

It introduces a femtosecond pump-probe Raman method to analyze polarization effects on coherent phonons in aligned nanotubes, highlighting differences between film and solution samples.

Findings

Coherent phonon spectra differ between film and solution samples.

Polarization dependence of phonon excitation varies with laser wavelength.

Resonant and off-resonant excitation behaviors are identified.

Abstract

We have used a femtosecond pump-probe impulsive Raman technique to explore the polarization dependence of coherent optical phonons in highly-purified and aligned semiconducting single-wall carbon nanotubes (SWCNTs). Coherent phonon spectra for the radial breathing modes (RBMs) exhibit a different monochromatic frequency between the film and solution samples, indicating the presence of differing exciton excitation processes. By varying the polarization of the incident pump beam on the aligned SWCNT film, we found that the anisotropy of the coherent RBM excitation depends on the laser wavelength, which we consider to be associated with the resonant and off-resonant behavior of RBM excitation.