Generation of a single attosecond pulse by gaseous atoms in a conical plasmonic nanostructure using a radially polarized laser beam

We propose a new theoretical method of producing a single attosecond pulse by high-order harmonic generation in hydrogen gaseous atoms above the conical plasmonic nanostructure (CPN) with a radially polarized laser field. The results show that the maximum amplification of the laser field above the structure apex about 4879 times can be provided by adjusting several physical characteristics of the structure and the incident light. Numerical studies show that the distribution of the amplification field above the CPN apex satisfies high-order harmonics generation (HHG) and attosecond pulse generation (APG) conditions by various incident laser beam intensities. Spectral analysis shows that this scheme can modulate the electron quantum paths. Selecting one quantum path, a broadband supercontinuum spectrum can be produced, which without phase compensation, directly generates a sharp isolated sub-20-attosecond pulse with a high signal-to-noise ratio.