▎ 摘　　要

The linear and nonlinear optical response of graphene are studied within a quantum-mechanical, full-band, steady-state density-matrix model. This nonpurtabative method predicts the saturatable absorption and saturable four-wave mixing of graphene. The model includes tau(1) and tau(2) time constants that denote carrier relaxation and quantum decoherence, respectively. Fits to existing experimental data yield tau(2) < 1 fs due to carrier-carrier scattering. tau(1) is found to be on the timescale from 250 fs to 550 fs, showing agreement with experimental data obtained by differential transmission measurements. (C) 2011 Optical Society of America