Because the electron relaxation time of graphene represents the
average time needed for electrons to dissipate their energy, thus it
should have connections with the intrinsic loss rate c0. To confirm
this idea, we calculate the absorption spectrum numerically by
varying the relaxation time from 0.05 to 4 ps while keeping other
parameters of the device unchanged. Fig. 2(a) shows the spectrums
for 0.05 ps < s < 0.4 ps, where the resonant absorption rate
increases from 38% at s = 0.05 ps to 100% at s = 0.4 ps, and the
bandwidth becomes narrower as s grows. The spectrums for
0.4 ps < s < 4 ps are displayed in Fig. 2(b). Compared with
Fig. 2(a), the resonant absorption rate drops now with the increase