High harmonics with spatially varying ellipticity

Jennifer L. Ellis*, Kevin M. Dorney, Daniel D. Hickstein, Nathan J. Brooks, Christian Gentry, Carlos Hernández-García, Dmitriy Zusin, Justin M. Shaw, Quynh L. Nguyen, Christopher A. Mancuso, G. S.Matthijs Jansen, Stefan Witte, Henry C. Kapteyn, Margaret M. Murnane

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

We present a method of producing ultrashort pulses of circularly polarized extreme ultraviolet (EUV) light through high-harmonic generation (HHG). HHG is a powerful tool for generating bright laser-like beams of EUV and soft x-ray light with ultrashort pulse durations, which are important for many spectroscopic and imaging applications in the materials, chemical, and nano sciences. Historically HHG was restricted to linear polarization; however, recent advances are making it possible to precisely control the polarization state of the emitted light simply by adjusting the driving laser beams and geometry. In this work, we gain polarization control by combining two spatially separated and orthogonally linearly polarized HHG sources to produce a far-field beam with a uniform intensity distribution, but with a spatially varying ellipticity that ranges from linearly to fully circularly polarized. This spatially varying ellipticity was characterized using EUV magnetic circular dichroism, which demonstrates that a high degree of circularity is achieved, reaching almost 100% near the magnetic M-edge of cobalt. The spatial modulation of the polarization facilitates measurements of circular dichroism, enabling us to measure spectrally resolved magnetic circular dichroism without the use of an EUV spectrometer, thereby avoiding the associated losses in both flux and spatial resolution, which could enable hyperspectral imaging of chiral systems. Through numerical simulations, we also show the generality of this scheme, which can be applied with either the discrete harmonic orders generated by many-cycle pulses or the high-harmonic supercontinua generated by few-cycle driving laser pulses. Therefore, this technique provides a promising route for the production of bright isolated attosecond pulses with circular polarization that can probe ultrafast spin dynamics in materials.

Original languageEnglish
Pages (from-to)479-485
Number of pages7
JournalOptica
Volume5
Issue number4
DOIs
Publication statusPublished - 20 Apr 2018

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