AG视讯厅:LLP Seminars

Capturing the Fastest Charge and Spin Dynamics in Materials Using High Harmonic Sources

Margaret Murnane, University of Colorado
Wed, 2019-07-31 10:00 - 10:50

X-ray science has undergone a revolution in the past decade. More than 50 years after the demonstration of the visible laser, it is finally not-only possible, but increasingly routine to make use of coherent light at wavelengths substantially shorter than the ultraviolet. Large- and small-scale coherent X-ray sources, including X-ray free electron lasers (XFELs) and high harmonic generation (HHG) sources, have demonstrated a broad range of applications. The past 8 years in particular have seen breakthrough advances – in the HHG source itself, in the development of new laser technologies, as well as in new experimental methodologies and applications.[1-6] Moreover, light science when combined with engineering has resulted in a tunable tabletop X-ray laser with femtosecond-to-attosecond pulse duration. The extreme quantum coherence of high harmonic (HHG) light sources makes it possible to control x-ray light using visible lasers, to the extent that it is now possible to produce short wavelength waveforms with controlled spectrum, temporal shape, polarization state, orbital and spin angular momentum and torque. This is important since most advanced applications of lasers require precise control over light. The ongoing development of ultrafast lasers in the mid-IR will make it increasingly practical to use HHG sources at even shorter soft and hard X-ray wavelengths.[7]

      This talk will present recent advances in high harmonic light sources, and also review selected applications in materials science and imaging. Exciting applications include imaging and spectroscopy of quantum materials, chemical and energy systems, as well as metrology in support of next-generation nanotechnologies. The high stability and spatial coherence of HHG sources have made it possible to achieve record EUV imaging – demonstrating the first sub-wavelength imaging at short wavelength using any light source, small or large — achieving 12.6 nm spatial resolution using 13.5 nm HHG beams. New materials behavior uncovered using HHG sources include the ultimate speed at which spins can be manipulated in materials. In recent work, we observed the ultrafast transfer of spin polarization from one magnetic sublattice to another in a half-metallic Heusler material. The observed transient enhancement of ferromagnetic ordering demonstrates direct manipulation of spins via light, thus providing a path towards spintronic logic devices such as switches that can operate on few fs or even faster timescales. Other exciting new capabilities include the ability to implement spatial-, interfacial- and depth-resolved maps of layered materials, the ability to find hidden phases with new properties in quantum materials, as well as the ability to probe thermal and elastic properties at the nanoscale.

[1].   Z. Tao et al., Science 353, 62 (2016).
[2].   C. Chen et al., PNAS 114, E5300 (2017).
[3].   X. Shi et al., Science Advances 5, eaav4449 (2019).
[4].   P. Tengdin et al., Science Advances 4, 9744 (2018).
[5].   K. Dorney et al., Nature Photonics 13, 123 (2019).
[6].   D. Gardner et al., Nature Photonics 11, 259 (2017).
[7].   D. Popmintchev et al, Physical Review Letters 120, 093002 (2018).

Dr. Margaret Murnane is Director of the US National Science Foundation STROBE Science and Technology Center on functional nanoimaging, a Fellow at JILA and a member of the Department of Physics and Electrical and Computer Engineering at the University of Colorado. She received her B.S and M.S. degrees from University College Cork, Ireland, and her Ph.D. degree in physics from the University of California at Berkeley in 1989. She runs a joint research group and a small laser company with her husband, Prof. Henry Kapteyn. Margaret's research interests have been in ultrafast laser and x-ray science. She is a Fellow of the American Physical Society, the Optical Society of America and the AAAS. Her honors include the Maria Goeppert-Mayer Award of the American Physical Society, a John D. and Catherine T. MacArthur Fellowship, and election to the National Academy of Sciences, the American Academy of Arts and Sciences, the American Phiosophical Society, and the Royal Irish Academy.