Dramatic dwindling of the power spectrum of high order harmonics by shrinking of the gap size in bowtie nanostructures

Abstract

Our work is based on high harmonic generation in a gaseous medium (helium ion), by exploiting gold bowtie nanostructures as laser field amplifiers. As the result of emission of a laser pulse, the wave function of the atom varies with time; so, it is necessary to solve 1D time-dependent Schrödinger equation by means of split operator method. By illumination of a short duration, long wavelength three color laser pulse inside the gap, the enhanced field not only changes with time, but also varies in space. In this work we considered this space inhomogeneity in linear and nonlinear schemes. We show that in nonlinear case, the plateau region is more extended. We also show that in larger gaps, cutoff occurs on higher frequencies. But limitation of electron motion in bowtie nanostructures leads to the choice of an optimum 16 nm gap size in our case. We predict that, by the superposition of supercontinuum harmonics, a 26 attosecond pulse can be generated.

Generation of High Order Harmonics from H2+ Molecule Ion by Using Homogenous and Inhomogeneous Laser Fields

“…In spectral range, the spectrum of high harmonics is displayed. One of the most important features of this process is the creation of the power spectrum, which drops down on the first harmonics, creating a plateau region, consisting of harmonics with mostly the same intensity and finally, an abrupt cutoff at the end of the curve [30]. By filtering several harmonics, isolated attosecond pulses are exhibited.…”