Extension of high-order harmonic generation cutoff via control of chirped laser pulses in the vicinity of metal nanostructure media

We use the local field enhancement induced by resonant plasmons within a metallic nanostructure to generate high-order harmonics in an 800 nm femtosecond laser pulse. Numerical results show that, with chirping an inhomogeneous field, the cutoff position of the HHG spectra is extended. By using suitable laser chirp and inhomogeneity parameters, only the short trajectories are selected. As a result, the obtained wide continuum spectrum shows that a little modulation can lead to the generation of short single attosecond pulses. To better understand the physical mechanism of this behavior, we analyze the time-frequency characteristics of HHG and perform semi-classical simulations.