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The first‐order Raman spectra of individual 8‐μm‐diam PAN‐derived carbon fibers which had been annealed at five temperatures from 1700 to 2800 °C are measured as a function of incident laser power from 1 to 140 mW. In all fibers studied, the Raman frequencies of the graphite G band at ca. 1580 cm−1 and the disordered‐induced D band at ca. 1360 cm−1 shift to lower frequency with increasing laser power. The largest shifts observed before the fiber is physically damaged are about 13 cm−1 at a laser power of 30 mW. The band positions decrease further at higher laser power, up to a maximum of about 20 cm−1 at 40 mW, and at powers above 30 mW the linewidths and the ID/IG intensity ratio change irreversibly as the fiber begins to erode. The irreversible changes extend several hundred μm away from the 2‐μm spot illuminated by the laser. The effects are attributed to laser heating. To quantify the degree of laser heating the temperature dependence of the Raman shift (G band) in pure bulk, highly oriented pyrolytic...

Laser heating effects in the characterization of carbon fibers by Raman spectroscopy