10 Aug 2007
Researchers from Germany and South Korea have demonstrated a reliable method for generating single, powerful extreme ultraviolet (XUV) pulses with a pulse length of just 170 attoseconds.
The dream of tracking and controlling electron dynamics on the atomic scale calls for techniques that offer resolution on the attosecond timescale. Attosecond pulses in the XUV to soft X-ray region of the spectrum constitute key elements for developing these techniques.
The researchers have generated 170 as (10-18 s) pulses delivering more than 106 photons per pulse at around 100 eV and a repetition rate of 3 kHz (New J. Phys. 9 243). The pulses are produced by ionizing neon with waveform-controlled near-infrared (NIR) laser pulses with a pulse length of less than 5 fs, and then spectrally filtering the emerging near-cutoff high-harmonic continuum with a broadband, chirped multilayer molybdenum–silicon mirror.
The method developed by the team avoids the need for a polarization gating, resulting in a substantially improved NIR-to-XUV conversion efficiency. The attosecond pulses generated are approximately 70% shorter than those previously generated without polarization control, and the photon fluxes produced are useful for time-resolved spectroscopy as they produce high-energy photons with a high photon flux.
Further developments in the field should soon allow the efficient generation of sub-100 as isolated pulses by driving pulses not shorter than 4 fs. Such controlled light fields and isolated attosecond pulses will open the door to accessing and controlling as yet unexplored processes in atoms, molecules, solids and nanostructures.