Shot Noise Limited Ultrafast Spectroscopy of Magnetic Thin Films Using Extreme Ultraviolet Light

Johnsen, Peter Chase

Graduate Thesis Or Dissertation

Shot Noise Limited Ultrafast Spectroscopy of Magnetic Thin Films Using Extreme Ultraviolet Light Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/tm70mw831

Abstract

High harmonic generation makes it possible to measure the fastest spin and charge dynamics in materials on femtosecond to attosecond timescales. However, the extreme nonlinear nature of the high harmonic process means that intensity fluctuations can limit measurement sensitivity. In this work, I present a noise-cancelled, tabletop high harmonic beamline for time-resolved reflection mode spectroscopy of magnetic materials. I use a reference spectrometer to independently normalize the intensity fluctuations of each harmonic order and also eliminate long term drift, which allows us to make spectroscopic measurements near the shot noise limit. These improvements allow us to significantly reduce the integration time required for high signal-to-noise (SNR) measurements of element-specific spin dynamics. I also present time- and element-resolved measurements of the spin dynamics of two half-metallic Heusler compounds, NiMnSb and Co₂MnGa. I show that we can directly control the spin dynamics of these materials with optical pulses due to their unique band structures, enabling the transfer of magnetization from one element to another. These results demonstrate our ability to precisely manipulate the magnetization of complex materials on femtosecond timescales. Looking forward, improvements in EUV flux, optical coatings, and grating design can further reduce the acquisition time for high SNR measurements by an additional 1-2 orders of magnitude, enabling dramatically improved sensitivity to spin, charge and phonon dynamics in multilayer and alloyed magnetic materials.

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