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Second-and third-harmonic generation in single-walled carbon nanotube films is experimentally investigated with the fundamental 1064 nm radiation from a Q-switched Nd:YAG laser. Measurements were performed both on commercially available carbon nanotubes and on samples of carbon nanotubes grown with a catalyst-free method. Third-harmonic generation was observed in both samples while only the sample grown with a catalyst-free method generated a second-harmonic signal. The quantum yield of second-and third-harmonic signal was proven to scale, respectively, with the second and third power of the pump pulse energy up to intensities of 10 9 W/cm 2 .

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Carbon nanotubes films have been prepared by low-velocity spraying of carbon nanosized particles on heated Si substrate. Studies reveal that by properly choosing the deposition temperature, well-aligned carbon nanotubes are self-assembled from the particles without a catalyst. Raman scattering and reflection high-energy electron diffraction show that the tubes are bundles of single-wall nanotubes. © 2002 American Institute of Physics. © 2002 American Institute of Physic

Second-and third-harmonic generation in single-wall carbon nanotube layers produced by low-velocity spraying was studied experimentally with the use of amplified 75 fs pulses of Cr : forsterite laser radiation within the range of pump pulse intensities up to the breakdown threshold. Harmonic-generation processes are shown to be ideally suited for the non-linear spectroscopy and structure analysis of carbon nanotubes, in many ways supplementary to Raman spectroscopy. The second-and third-harmonic yields scale as quadratic and cubic functions, respectively, of the pump pulse energy up to pump intensities of 10 12 W cm −2 , indicating the perturbative regime of non-linear-optical interactions and suggesting a convenient calibration for the second and third harmonics employed as spectroscopic probes. Comparison of harmonicgeneration data with absorption spectra of carbon-nanotube layers reveals an important role of quantum confinement effects in the non-linear coherent scattering of light from carbon nanotubes. Femtosecond pulses of Cr : forsterite laser radiation also generate the fifth optical harmonic at 251 nm in the glass substrate of carbon-nanotube samples, which can be employed for UV spectroscopy and subwavelength-resolution non-linear microscopy of carbon nanotubes.