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.
The development of new optical materials and metamaterials has seen a natural progression toward both nanoscale geometries and dynamic performance. The development of these materials, such as optical metasurfaces which impart discrete, spatially dependent phase shifts on incident light, often benefits from the measurement of transmitted or reflected phase. Careful measurement of phase typically proves difficult to implement, due to high measurement sensitivity to practically unavoidable environmental sources of noise and drift. To date, no characterization technique has yet emerged as a frontrunner for these applications. This challenge is addressed using a custom‐designed three‐beam Mach–Zehnder interferometer capable of continuously referenced measurement of both phase and transmittance, resulting in a 10× reduction of noise and drift and phase measurement standard deviation over 10 min of 0.56° and over 16 h of 2.8°. High measurement stability provided by this method enables samples to be easily characterized under dynamic conditions. Temperature‐dependent measurements are demonstrated with phase‐change material vanadium dioxide (VO2), and with wavelength‐dependent measurements of a dielectric Huygens metasurface supporting a characteristic resonant reflection peak. A Fourier‐based signal filtering technique is applied, reducing measurement uncertainty to 0.13° and enabling discernment of monolayer thickness variations in 2D material MoS2.
more » « less- Award ID(s):
- 1654765
- NSF-PAR ID:
- 10460765
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 7
- Issue:
- 24
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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