Ultrashort-attosecond-pulse generation by reducing harmonic chirp with a spatially inhomogeneous electric field

We theoretically study high-order harmonic generation from an inhomogeneous field originated by the interaction between an ultrashort laser pulse and a gold nanostructure and demonstrate that ultrashort isolated attosecond pulses can be generated by reducing the harmonic chirp with the spatially inhomogeneous electric field. It can be found that the instants of ionized electrons coming back to the core are highly concentrated in the case of the spatially inhomogeneous electric field and a broadband supercontinuum harmonic spectrum with less chirp can be produced. Then an isolated 127-as pulse close to the Fourier transform limit can be directly generated without phase compensation.