▎ 摘　　要

In this paper, influences of finite length on optical properties of graphene nanoribbons have been investigated. Discrete electronic states, which created by finite length barriers, are calculated using third nearest neighbor tight binding jointed with quantum confinement of Bloch theory. Fermi Golden rule within Gradient approximation has been used to study optical properties of zigzag and armchair graphene nanoribbons as a result of these discrete states. It is shown that the absorption spectra strongly have depended on length and edge structures of graphene nanoribbons. Our calculation has shown the threshold excitation frequency decrease to its infinite length value as length increases in metallic armchair, while in nonmetallic armchair and zigzag; this frequency does not change sensitively. Number of absorption peaks in different structures of graphene nanoribbons has been investigated and shown these absorption peaks group together as length increased. Maximum absorption and stop band frequencies have investigated in different lengths and edges structures. It has shown that these frequencies have little shift with length. The predicted results can be verified by the experimental measurements, which have been done for infinite GNRs and as length increases, results converge to previous reports on optical absorption spectrum of infinite length graphene nanoribbons.