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



Q112, W&N-building, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam

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

Henry Kapteyn, Department of Physics, JILA, and NSF ERC in EUV Science and Technology, University of Colorado and NIST, Boulder

Stefan Witte





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).

Henry Kapteyn