Setup of focused laser system where LII in CNTs is achieved. Insets (a) and (b) show the optical image and (as-captured) intensity profile of a typical LII of CNT, respectively.
A typical (corrected) intensity profile of LII in CNTs. A rescaled Planck blackbody wavelength distribution function at provides an excellent fitting to the experimental data with a calculated reduced value of 1.24.
(a) Time evolution of LII intensity at selected wavelengths. (b) Evolution of temperature of the LII as calculated with Eq. (2) corresponding to the intensity data in (a). The focused laser beam irradiates on the sample from .
(a) Very bright LII just after the onset of laser. (b) Sustain glow of LII after of continuous laser irradiation. (c) SEM image of a crater formed during LII.
SEM images showing (a) top-view of an LII crater laser pruned to reveal its cross-section, (b) cross-sectional view of the crater, (c) and (d) magnified images of portions of the outer ring to the left and right sides of the central hole, respectively.
Raman spectroscopy at various radial positions across the LII crater. Decreasing trend in the ratio of vs is observed as the laser beam scans toward the center of the crater.
SEM images of craters formed by different durations of LII.
SEM images of craters formed by different laser powers.
LII intensity at various operating pressures. Inset (a) shows two general trends—one with stable intensity and one with a sharp peak followed by an even sharper drop in intensity. Inset (b) shows that in higher vacuum, LII intensity increases with increasing laser power. Inset (c) sows that the time for thermal runaway to occur reduces for higher pressures.
LII craters formed at (a) 1 mTorr, (b) 10 mTorr, and (c) 100 mTorr vacuum conditions. Massive destruction of CNTs is observed for (b) and (c).
LII at various gaseous environments. Laser was irradiated on the samples after . Thermal runaway do not occur in argon, carbon dioxide, and nitrogen gas environments even at low vacuum condition of 1.5 Torr. The display of thermal runaway in oxygen environment shows that oxygen is the gas responsible for thermal runaway during LII.
Craters formed during LII in various gaseous environments. Massive destruction of CNTs in oxygen shows that thermal runaway had occurred. In contrast, most of the CNTs in argon, carbon dioxide, and nitrogen gas survived to give sustained LII.
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