Generation of bright isolated attosecond soft X-ray pulses driven by multicycle midinfrared lasers.

Authors:
Dr. Agnieszka Jaron-Becker, PhD
Dr. Agnieszka Jaron-Becker, PhD
University of Colorado at Boulder
Associate Research Professor
Boulder, CO | United States
Dimitar Popmintchev
Dimitar Popmintchev
University of Colorado at Boulder
United States
popmintchev, PhD
popmintchev, PhD

Atomic and Molecular Optics

Proc Natl Acad Sci U S A 2014 Jun 21;111(23):E2361-7. Epub 2014 May 21.

JILA and Department of Physics, University of Colorado Boulder, Boulder, CO 80309-0440;

High harmonic generation driven by femtosecond lasers makes it possible to capture the fastest dynamics in molecules and materials. However, to date the shortest subfemtosecond (attosecond, 10(-18) s) pulses have been produced only in the extreme UV region of the spectrum below 100 eV, which limits the range of materials and molecular systems that can be explored. Here we experimentally demonstrate a remarkable convergence of physics: when midinfrared lasers are used to drive high harmonic generation, the conditions for optimal bright, soft X-ray generation naturally coincide with the generation of isolated attosecond pulses. The temporal window over which phase matching occurs shrinks rapidly with increasing driving laser wavelength, to the extent that bright isolated attosecond pulses are the norm for 2-µm driving lasers. Harnessing this realization, we experimentally demonstrate the generation of isolated soft X-ray attosecond pulses at photon energies up to 180 eV for the first time, to our knowledge, with a transform limit of 35 attoseconds (as), and a predicted linear chirp of 300 as. Most surprisingly, advanced theory shows that in contrast with as pulse generation in the extreme UV, long-duration, 10-cycle, driving laser pulses are required to generate isolated soft X-ray bursts efficiently, to mitigate group velocity walk-off between the laser and the X-ray fields that otherwise limit the conversion efficiency. Our work demonstrates a clear and straightforward approach for robustly generating bright isolated attosecond pulses of electromagnetic radiation throughout the soft X-ray region of the spectrum.

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Source
http://dx.doi.org/10.1073/pnas.1407421111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4060714PMC
June 2014
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