A new model is proposed to investigate femtosecond laser pulse train processing of dielectrics by including the laser wave properties in the photon particle properties based plasma model. In the case studies, the pulse duration is 50fs and the pulse delays are 0, 25, 50 and 75fs. Both the laser waveparticle duality and transient localized changes of material properties are considered in the proposed model, and the formation mechanism of sub-wavelength ripples is revealed. This study shows that the interference between surface plasmons and laser field plays a key role in the formation of sub-wavelength ripples for which the excitation of surface plasmons is necessary. The predicted period of sub-wavelength ripples is in agreement with the experiments. © 2012 IOP Publishing Ltd.