Carbon nanotubes prepared by catalytic (CO) disproportionation were studied using TEM, XRD, UPS, XPS, and optical spectroscopies. In comparison with graphite, the carbon nanotubes show greater interplanar distance, smaller work function, steeper Fermi edge, negative core-level shift, and stronger plasma excitation. Their valence band is basically the same as that of graphite, with lower intensity in the binding energy region of 2-7 eV. The carbon nanotubes exhibit a strong optical limiting effect, superior to both carbon black and C 60. [S0031-9007(99)08764-5]

Optical limiting effects in multiwalled carbon nanotubes have been observed in the visible and infrared spectral regions with nanosecond laser pulses. The multiwalled carbon nanotubes investigated include those suspended in distilled water and embedded in polymethyl methacrylate films. Among all the samples measured, the limiting performance of the carbon nanotube suspension is the best with the limiting threshold determined to be ∼1, 5, and 13 J/cm2 at 532, 700, and 1064 nm, respectively. The possible mechanism for the observed effects is discussed.

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Recent advance of lithium niobate microphotonic devices enables the exploration of intriguing nonlinear optical effects. We show complex nonlinear oscillation dynamics in high-Q lithium niobate microresonators that results from unique competition between the thermo-optic nonlinearity and the photorefractive effect, distinctive to other device systems and mechanisms ever reported. The observed phenomena are well described by our theory. This exploration helps understand the nonlinear optical behavior of high-Q lithium niobate microphotonic devices which would be crucial for future application of on-chip nonlinear lithium niobate photonics.