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Fundamental processes in atoms, molecules, and condensed matter systems are triggered or mediated by the motion of electrons inside or between atoms. On atomic length scales, these dynamics occur on timescales ranging from tens to thousands of attoseconds (1 attosecond [as] = 10e-18 s). Previous breakthroughs in laser science have led to reliable sources of isolated attosecond XUV pulses allowing direct time-domain observation and coherent control of these previously inaccessible microscopic dynamics.
Recently, advances in the generation of isolated attosecond XUV pulses have been enabled by waveform controlled sub-4fs, 400µJ NIR driver pulses. Such short and energetic drive pulses have been delivered without the use of adaptive pulse shaping devices, but, by implementation of a novel intermediate hybrid prism/positive dispersion chirped mirror compressor. Further development of XUV multilayer chirped mirror fabrication and advanced XUV filtering allows utilization of the ultra-broadband and upshifted high-harmonic spectral cutoff regions resulting from these new drive pulses. Intense, isolated, sub-100 attosecond pulses are now within reach. Concurrently, the application of attosecond metrology, utilizing these isolated attosecond pulses, has been expanded. In atoms, strong field light-induced electron tunneling has been observed, leading to a new technique - "attosecond tunneling" - for probing short-lived, transient states of atoms or molecules with high temporal resolution. This technique allows observation of inner-atomic relaxation processes in atomic systems. Additionally, the atomic-transient recorder, previously developed through application to isolated atomic systems has now been applied to condensed matter systems. Attosecond spectroscopy in condensed matter provides direct time-domain access to attosecond charge dynamics in solids and on surfaces. Our first proof-of-principle measurements in single-crystal tungsten, made with sub-100 attosecond resolution, reveal transient electron transport characteristics in the upper-conduction bands. Improvements in this technique and our planned application of this technology to additional metals and adsorbate/substrate systems will be described. |
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