|A nanofunnel generates extreme-UV light from IR pulses. At the entrance, IR light (red) strikes xenon gas (green particles). Surface-plasmon polariton fields (wave pattern) concentrate near the exit of the structure. Extreme UV light (purple) is generated in the enhanced fields in the xenon and exits the funnel through the small opening; IR is backreflected. (Image: Christian Hackenberger)
Daejeon, South Korea--A team of scientists from Korea, Germany, and the U.S. has created a xenon-gas-filled silver nanofunnel that accepts IR light in its large end, and, through high-harmonic generation, emits extreme-UV radiation from its small end.1 The funnel's 100-nm-diameter small end also acts as a wavelength filter, rejecting the 800-nm-wavelength IR radiation but allowing the 20-nm-wavelength extreme UV to pass. The uV is in the form of a string of attosecond pulses. The team includes researchers from the Korea Advanced Institute of Science and Technology (KAIST; Daejeon, South Korea), the Max Planck Institute of Quantum Optics (MPQ; Garching, Germany), and Georgia State University (GSU; Atlanta, Georgia).
Field concentrated by a factor of a few hundred
The slightly elliptical funnel is a few microns long. The IR laser pulses, which are a few femtoseconds in duration and produced at a 75 MHz rate, create electron-density fluctuations on the inside of the funnel, resulting in surface-plasmon polaritons that are concentrated as they travel toward the tip of the funnel. “The field on the inside of the funnel can become a few hundred times stronger than the field of the incident IR light," says Mark Stockman from GSU. "This enhanced field results in the generation of extreme-UV light in the xenon gas."
“Due to their short wavelength and potentially short pulse duration reaching into the attosecond domain, extreme-UV light pulses are an important tool for the exploration of electron dynamics in atoms, molecules, and solids,” says Seung-Woo Kim from KAIST.
Electrons move at attosecond timescales. To capture a moving electron, light pulses are needed that are shorter than the timescale of the motion. Attosecond light flashes have become a familiar tool in the exploration of electron motion. With conventional techniques, measurements can only be repeated a few thousand times per second, as opposed to the 75 MHz rate for the nanofunnel. “We assume that the few-femtosecond light flashes consist of trains of attosecond pulses,” says Matthias Kling, group leader at MPQ. “With such pulse trains, we should be able to conduct experiments with attosecond time resolution at very high repetition rate.”
1. In-Yong Park et al., Nature Photonics, 16 October 2011, Doi: 10.1038/NPHOTON.2011.258.