The measured PAN-based carbon fiber is 4.3 lm in diameter
and 12.336 mmin length. A 514.5 nm laser is focused in the middle
of the test fiber and the Raman spectra are recorded under different
heating power conditions. Figs. 4 and 5 show the measured
D-band, G-band and 2D-band Raman peaks.
Figs. 4 and 5 are the original measured Raman spectra of the
test fiber. The G-band/D-band intensity ratio is 2.36, indicating
that the test fiber is highly graphitized and suitable for Raman
measurement. The red lines in Figs. 4 and 5 represent the downshifted
Raman peaks; the laser powers are the measured values
out of 50 microscope objective. All the Raman peaks are fitted
using the same Gauss–Lorenz function.
Fig. 6 shows the shifted Raman frequency versus laser power
curves: (a) G-band around 1580 cm1; (b) 2D-band around
2700 cm1. It is seen that both G-band and 2D-band Raman frequencies
are sensitive to the temperature. Because the G-band Raman
peak is sharper and has higher intensity, it is used to monitor
the local temperature of the test fiber.
Fig. 7 shows the measured D-band and G-band Raman frequencies
varied with the environment temperature. The linear regression
result of the measured data is shown in Fig. 8.
The linear regression in Fig. 8 gives a slope of 0.03035 cm1/
C, which agrees with the published experimental data [17]. Using
this slope, the local temperature of the test fiber can be estimated.
Fig. 9 shows the temperature rise in the middle of the test fiber
due to different laser powers. The inset (a) is the measured thermal
conductivity and the inset (b) is the temperature distributions