Plasmonic generation of ultrashort extreme-ultraviolet light pulses

Abstract

Ultrashort extreme-ultraviolet pulses are a key tool in time-resolved spectroscopy for the investigation of electronic motion in atoms(1,2), molecules(3) and solids(4). High-harmonic generation is a well-established process for producing ultrashort extreme-ultraviolet pulses by direct frequency upconversion of femtosecond near-infrared pulses(5-7). However, elaborate pump-probe experiments performed on the attosecond timescale(8,9) require continuous efforts to improve the spatiotemporal coherence and also the repetition rate of the generated pulses. Here, we demonstrate a three-dimensional metallic waveguide for the plasmonic generation of ultrashort extreme-ultraviolet pulses by means of field enhancement using surface-plasmon polaritons. The intensity enhancement factor reaches a peak of similar to 350, allowing generation up to the 43rd harmonic in xenon gas, with a modest incident intensity of similar to 1 x 10(11) W cm(-2). The pulse repetition rate is maintained as high as 75 MHz without external cavities. The plasmonic waveguide is fabricated on a cantilever microstructure and is therefore suitable for near-field spectroscopy with nanometre-scale lateral selectivity.