High harmonic generation (HHG) makes it possible to measure 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. Here we present a noise-canceled, tabletop high harmonic beamline for time-resolved reflection mode spectroscopy of magnetic materials. We use a reference spectrometer to independently normalize the intensity fluctuations of each harmonic order and eliminate long term drift, allowing 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. Looking forward, improvements in the HHG flux, optical coatings, and grating design can further reduce the acquisition time for high SNR measurements by 1–2 orders of magnitude, enabling dramatically improved sensitivity to spin, charge, and phonon dynamics in magnetic materials.
A beamline for ultrafast extreme ultraviolet magneto-optical spectroscopy in reflection near the shot noise limit
Peter C. Johnsen, Sinéad A. Ryan, Christian Gentry, Anya Grafov, Henry Kapteyn, Margaret Murnane; A beamline for ultrafast extreme ultraviolet magneto-optical spectroscopy in reflection near the shot noise limit. Rev. Sci. Instrum. 1 March 2023; 94 (3): 033001. https://doi.org/10.1063/5.0127119
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