Generation of isolated attosecond pulses in bowtie-shaped nanostructure with three-color spatially inhomogeneous fieldsProject supported by the National Natural Science Foundation of China (Grants Nos. 11404153, 11175076, 11135002, and 11405077) and the Fundamental Research Funds for the Central Universities of China (Grant Nos. lzujbky-2014-10, lzujbky-2014-13, and lzujbky-2014-14).

We theoretically investigate high-order harmonic generation in a two-color multi-cycle inhomogeneous field combined with a 27th harmonic pulse. By considering a bowtie-shaped gold nanostructure, the spatiotemporal profiles of enhanced plasmonic fields are obtained by solving the Maxwell equation using finite-domain time-difference method. Based on quantum-mechanical and classical models, the effect of 27th harmonic pulse, temporal profile of enhanced plasmonic field and inhomogeneity on supercontinuum generation are analyzed and discussed. As a result, broadband supercontinuum can be generated from our approach with optimized gap size of nanostructure. Moreover, these results are not sensitively dependent on the relative phase in the two-color field.