TY - JOUR
AU - Jennifer Ellis
AU - Kevin Dorney
AU - Daniel Hickstein
AU - Nathan Brooks
AU - Christian Gentry
AU - Carlos Hernández-García
AU - Dmitriy Zusin
AU - Justin Shaw
AU - Quynh Nguyen
AU - Christopher Mancuso
AU - G. Jansen
AU - Stefan Witte
AU - Henry Kapteyn
AU - Margaret Murnane
AB - 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.
BT - Optica
DA - 2018-04
DO - 10.1364/OPTICA.5.000479
N2 - 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.
PY - 2018
EP - 479
T2 - Optica
TI - High harmonics with spatially varying ellipticity
UR - https://www.osapublishing.org/optica/fulltext.cfm?uri=optica-5-4-479\&id=385612
VL - 5
ER -