Abstract
Plasmonic high-harmonic generation (HHG) drew attention as a means of producing coherent extreme ultraviolet (EUV) radiation by taking advantage of field enhancement occurring in metallic nanostructures. Here a metal-sapphire nanostructure is devised to provide a solid tip as the HHG emitter, replacing commonly used gaseous atoms. The fabricated solid tip is made of monocrystalline sapphire surrounded by a gold thin-film layer, and intended to produce EUV harmonics by the inter- and intra-band oscillations of electrons driven by the incident laser. The metal-sapphire nanostructure enhances the incident laser field by means of surface plasmon polaritons, triggering HHG directly from moderate femtosecond pulses of ∼0.1 TW cm−2 intensities. The measured EUV spectra exhibit odd-order harmonics up to ∼60 nm wavelengths without the plasma atomic lines typically seen when using gaseous atoms as the HHG emitter. This experimental outcome confirms that the plasmonic HHG approach is a promising way to realize coherent EUV sources for nano-scale near-field applications in spectroscopy, microscopy, lithography and atto-second physics.
Highlights
Plasmonic high-harmonic generation (HHG) drew attention as a means of producing coherent extreme ultraviolet (EUV) radiation by taking advantage of field enhancement occurring in metallic nanostructures
High-harmonic generation (HHG) is a coherent frequencyconversion process arising from gaseous atoms[1,2,3,4] or crystalline solids[5,6,7] when they are irradiated by an intense laser pulse
The laser pulses employed in HHG need to be able to deliver strong intensities of B10 TW cm À 2, chirped pulse amplification (CPA) is commonly adopted to raise the peak power of femtosecond pulses emanating from an oscillator[8,9]
Summary
Plasmonic high-harmonic generation (HHG) drew attention as a means of producing coherent extreme ultraviolet (EUV) radiation by taking advantage of field enhancement occurring in metallic nanostructures. Efforts have been made to take advantage of the strong field enhancement that occurs in nanostructures to attain the field intensities needed for HHG directly from a moderate-power laser oscillator This plasmonic nanostructure-assisted HHG is intended to build a compact extreme ultraviolet or X-ray source by removing the bulky chirped pulse amplification process, and more importantly, seek to establish a nano-scale basis for conducting spectroscopy[10], microscopy[11], lithography[12] and atto-second physics[13], on a single-molecule level. Increasing the gas supply pressure results in no noticeable effect in multiplying the emitter density in the hot-spot volume because gaseous atoms rapidly disperse into vacuum by adiabatic expansion[28] In this investigation, we designed a nanostructure that replaces gaseous atoms with a monocrystalline sapphire tip that functions as a solid HHG emitter. This result validates that the metalsapphire nanostructure devised in this study successfully copes with the difficulty of securing sufficient gaseous atoms within the a z x
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