Abstract
Plasmon resonances are known to amplify the electromagnetic fields near metallic nanostructures, providing a promising scheme to generate extreme-ultraviolet harmonics using low power drivings. During high-order harmonic generation (HHG), the driving and harmonic fields accumulate a phase difference as they propagate through the target. In a typical set-up -a laser focused into a gas jet- the propagation distances amount to several wavelengths, and the cumulative phase-mismatch affects strongly the efficiency and properties of the harmonic emission. In contrast, HHG in metallic nanostructures is considered to overcome these limitations, as the common sources of phase mismatch -optical density and focusing geometry- are negligible for subwavelength propagation distances. We demonstrate that phase matching still plays a relevant role in HHG from nanostructures due to the non-perturbative character of HHG, that links the harmonic phase to the intensity distribution of the driving field. Our computations show that widely used applications of phase matching control, such as quantum path selection and the increase of contrast in attosecond pulse generation, are also feasible at the nanoscale.
Highlights
high-order harmonic generation (HHG) driven by strong laser fields is demonstrated as a reliable scheme for the generation of short-wavelength coherent radiation
We demonstrate that phase matching still plays a relevant role in HHG from nanostructures due to the non-perturbative character of HHG, that links the harmonic phase to the intensity distribution of the driving field
We present full calculations of HHG in bow-tie nano antennas filled with argon, which includes harmonic generation, propagation and the ab-initio computation of the resonant enhancement of the incident field
Summary
HHG driven by strong laser fields is demonstrated as a reliable scheme for the generation of short-wavelength coherent radiation. Its extraordinary characteristics reserve HHG its own niche among other sources of high-frequency radiation. HHG has been boosted into the soft x-ray spectral region using mid-IR drivings and high-pressure gases in hollow wave-guides [1]. HHG conveys the production of short-wavelength radiation in the form of ultrashort pulses, with subfemtosecond durations [2]. Different techniques allow to generate isolated attosecond pulses, even using multicycle drivers [3] and references therein). HHG is a fundamental tool for spectroscopy, and for time-dependent measurements at the attosecond scale [4, 5]
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