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PHYSICS COLLOQUIUM


"Ultrafast coherent x-rays from tabletop lasers—a new tool for science and technology"


HENRY KAPTEYN
University of Colorado

ABSTRACT 

The discovery of x-rays made possible not-only new medical technologies, but also allowed man to “see” for the first time at the atomic scale, revolutionizing our understanding of matter. Efforts to bring x-ray techniques to femtosecond time-scales—the fundamental atomic time scale— have been ongoing for the past ~¼ century, and are now providing new insight into the behavior of matter. Key to this work has been to understand the coherent high-order harmonic generation (HHG) upconversion process. HHG allows for the light from a high-power femtosecond laser to be coherently upconverted from the infrared into the soft x-ray region of the spectrum, with each x-ray photon resulting from the coherent combination of hundreds or even thousands of photons from the driving laser. The resultant ultrashort-pulse HHG x-ray sources allow us to probe, using a tabletop setup, the fastest charge, spin and energy transport processes. The capabilities of these sources have increased dramatically with our recent demonstration of bright sources with photon energy >1 keV.[1-4] Recent applications include probing the dynamics of the quantum exchange interaction fundamental to magnetic materials;[5-7] the use of coherent HHG light for tabletop nano-imaging with record resolution;[9] and studies of the physical limits of energy flow at the nanoscale.[9,10]
  1. T. Popmintchev, et al, The Attosecond Nonlinear Optics of Bright Coherent X-Ray Generation, Nature Photonics 4, 822 (2010).
  2. M.C. Chen et al., Bright, Coherent, Ultrafast Soft X-Ray Harmonics Spanning the Water Window from a Tabletop Light Source, PRL 105, 173901 (2010).
  3. T. Popmintchev et al., Phase matching of high harmonic generation in the soft and hard X-ray regions of the spectrum, PNAS 106, 10516 (2009).
  4. T. Popmintchev et al, Bright Coherent Ultrahigh Harmonics in the keV X-ray Regime from Mid-Infrared Femtosecond Lasers, Science 336, 1287 (2012).
  5. C. La-O-Vorakiat et al., Ultrafast Magneto-Optics at the M-edge Using Tabletop HHG, PRL 103, 257402 (2009).
  6. C. La-O-Vorakiat et al, Ultrafast Demagnetization Measurements Using Extreme Ultraviolet Light: Comparison of Electronic and Magnetic Contributions, Physical Review X 2, 011005 (2012).
  7. S. Mathias et al, Probing the timescale of the exchange interaction in a ferromagnetic alloy, PNAS 109, 4792 (2012).
  8. M. Seaberg et al., Ultrahigh 22nm Resolution Coherent Diffractive Imaging using a Desktop 13nm High Harmonic Source, Optics Express 19, 22470 (2011).
  9. M. Siemens et al., Measurement of quasi-ballistic heat transport across nanoscale interfaces using ultrafast coherent soft x-ray beams, Nature Materials 9, 26 (2010).
  10. D. Nardi et al, Probing Thermomechanics at the Nanoscale: Impulsively Excited Pseudosurface Acoustic Waves in Hypersonic Phononic Crystals, Nano Letters 11, 4126 (2011).



Thursday, November 29, 2012
Hawking Auditorium, 4:00 p.m.
Mitchell Physics Institute


Department of Physics and Astronomy
Texas A&M University

(Refreshments to be served at 3:45pm in the Penrose Plaza)

Host: Alexey Belyanin