  The generation of high-order harmonics in quasi-one-dimensional graphene
nanoribbons (GNRs) initiated by intense coherent radiation is investigated. A
microscopic theory describing the extreme nonlinear optical response of GNRs is
developed. The closed set of differential equations for the single-particle
density matrix at the GNR-strong laser field multiphoton interaction is solved
numerically. The obtained solutions indicate the significance of the bandgap
width and Fermi energy level on the high-order harmonic generation process in
GNRs.
