Saturday, November 29, 2008

Ultraviolet pulses close in on 1 fs regime

Deep ultraviolet (DUV) pulses with a duration of just 3.7 femtoseconds have been generated by researchers at the Max-Planck-Institute for Quantum Optics in Germany. The pulses are said to be the shortest ever observed at this wavelength range and could allow the team to influence the outcome of chemical reactions by controlling the motion of electrons in molecules. (Optics Express 16 18956)

Previously, the shortest pulses in the DUV (wavelengths shorter than 300 nm) had a duration of 8 femtoseconds. Much of the research effort focused on compressing the ultraviolet pulses after they had been generated, which is a formidable challenge as this requires precise dispersion control.

Here, Ulrich Graf and colleagues take a different approach. They upconvert 780 nm, 0.25 mJ pulses with a duration of 6 femtosecond pulses directly into the UV range by means of harmonic generation in a noble gas jet.

The resulting 3.7 femtosecond pulses are characterized using a dispersion-minimized SD-FROG approach and have energies in excess of 1.4µJ. The conversion efficiency is approximately 0.6%.

The group is now hoping to extend its approach to generate ultrashort pulses in the vacuum ultraviolet (VUV) spectral range (wavelengths less than 180 nm). "In the VUV, matter absorbs light even more and this spectral range will offer plenty of opportunities to explore and control the microcosm on an ultrafast scale," said Goulielmakis. "At the same time, we anticipate that these pulses will be substantially shorter and will approach the 1 femtosecond frontier."

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