Single-grating monochromator for extreme-ultraviolet ultrashort pulses

Frassetto, Fabio; Cacho, Céphise; Froud, C. A.; Turcu, Ioan; Villoresi, Paolo; Bryan, William A.; Springate, E.; Poletto, Luca

doi:10.1364/oe.19.019169

Cited by 156 publications

(147 citation statements)

References 32 publications

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“…The latter were obtained by high harmonic generation in an Argon gas jet. The 17th harmonic athω probe = 26.3 eV was selected with a time-preserving grating monochromator [13] and used to measure photoelectron distributions from the sample. The probe polarization was fixed along the x axis [ Fig.…”

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confidence: 99%

Ultrafast momentum imaging of pseudospin-flip excitations in graphene

et al. 2017

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The pseudospin of Dirac electrons in graphene manifests itself in a peculiar momentum anisotropy for photoexcited electron-hole pairs. These interband excitations are in fact forbidden along the direction of the light polarization and are maximum perpendicular to it. Here, we use time-and angle-resolved photoemission spectroscopy to investigate the resulting unconventional hot carrier dynamics, sampling carrier distributions as a function of energy, and in-plane momentum. We first show that the rapidly-established quasithermal electron distribution initially exhibits an azimuth-dependent temperature, consistent with relaxation through collinear electron-electron scattering. Azimuthal thermalization is found to occur only at longer time delays, at a rate that depends on the substrate and the static doping level. Further, we observe pronounced differences in the electron and hole dynamics in n-doped samples. By simulating the Coulomb-and phonon-mediated carrier dynamics we are able to disentangle the influence of excitation fluence, screening, and doping, and develop a microscopic picture of the carrier dynamics in photoexcited graphene. Our results clarify new aspects of hot carrier dynamics that are unique to Dirac materials, with relevance for photocontrol experiments and optoelectronic device applications. DOI: 10.1103/PhysRevB.96.020301The existence of anisotropic photocarrier distributions in graphene was predicted [1,2] and observed in optical pump-probe experiments [3-6], which showed a pronounced difference in the time-dependent optical response for different probe polarizations. The decay of the anisotropy extracted in this manner was attributed to optical phonon emission [2][3][4][5]7,8]. However, a complete picture for these nonequilibrium phenomena can only be obtained by tracking both carrier energy and momentum in the time domain.Here we use time-and angle-resolved photoemission spectroscopy (tr-ARPES) at extreme ultraviolet (XUV) wavelengths to track the temporal evolution of the photoexcited carrier distribution as a function of energy and momentum. We establish a hierarchy of events that redistribute carriers on the Dirac cone, including the formation of a quasithermal state with an azimuth-dependent anisotropic electron temperature, which indicates that primary thermalization occurs through collinear electron-electron scattering. Azimuthal relaxation through phonon emission and noncollinear electron-electron scattering plays a role only at later time delays and is found to be strongly influenced by the substrate and the type of static doping of the graphene layer. Furthermore, the finite doping in our samples breaks the electron-hole symmetry and results in different dynamics for electrons and holes. Microscopic simulations of the anisotropic carrier dynamics indicate that the observed dynamics are due to a subtle interplay between doping that affects the scattering phase space and substrate screening which reduces the influence of electron-electron scattering.* sven.aeschlimann@mpsd.mpg.de † is...

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confidence: 99%

Ultrafast momentum imaging of pseudospin-flip excitations in graphene

et al. 2017

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“…[20][21][22] The fundamental laser, a multi-pass titanium-sapphire amplifier, produced up to 10 mJ, 800 nm pulses with a FWHM of 30 fs at 1 kHz. For time resolved measurements the laser output was split 20:80 for probe:pump (Fig.…”

Section: Methodsmentioning

confidence: 99%

“…A full description of the monochromator is given elsewhere. 22 The measurements presented here used a grating with groove density of 500 gr/mm and a theoretical energy resolution of E = 1.0 eV at 62 eV.…”

Section: A Monochromation and Calibrationmentioning

confidence: 99%

A simple electron time-of-flight spectrometer for ultrafast vacuum ultraviolet photoelectron spectroscopy of liquid solutions

Arrell

Ojeda

Sabbar

et al. 2014

Review of Scientific Instruments

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Articles you may be interested inWe present a simple electron time of flight spectrometer for time resolved photoelectron spectroscopy of liquid samples using a vacuum ultraviolet (VUV) source produced by high-harmonic generation. The field free spectrometer coupled with the time-preserving monochromator for the VUV at the Artemis facility of the Rutherford Appleton Laboratory achieves an energy resolution of 0.65 eV at 40 eV with a sub 100 fs temporal resolution. A key feature of the design is a differentially pumped drift tube allowing a microliquid jet to be aligned and started at ambient atmosphere while preserving a pressure of 10 −1 mbar at the micro channel plate detector. The pumping requirements for photoelectron (PE) spectroscopy in vacuum are presented, while the instrument performance is demonstrated with PE spectra of salt solutions in water. The capability of the instrument for time resolved measurements is demonstrated by observing the ultrafast (50 fs) vibrational excitation of water leading to temporary proton transfer.

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“…The OPM gives higher throughput than the CDM, since it has been theoretically demonstrated and experimentally measured that the OPM peak diffraction efficiency is close to the reflectivity of the coating at the altitude angle [29,30]. Both geometries have still been applied to the realization of ultrafast monochromators for HHs in the XUV [31][32][33][34]. Since the gratings in the OPM monochromators are operated in parallel light, we will compare the two configurations with plane gratings.…”

Section: Single-grating Monochromators For Ultrashort Pulsesmentioning

confidence: 99%

Design Study of Time-Preserving Grating Monochromators for Ultrashort Pulses in the Extreme-Ultraviolet and Soft X-Rays

et al. 2017

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Abstract:The design of grating-based instruments to handle and condition coherent ultrafast pulses in the extreme-ultraviolet is discussed. The main application of such instruments is the monochromatization of high-order laser harmonics and free-electron-laser pulses in the femtosecond time scale. Broad-band monochromators require the use of diffraction gratings at grazing incidence. A grating can be used for the spectral selection of ultrashort pulses without altering the pulse duration in a significant way, provided that the number of illuminated grooves is equal to the resolution. We discuss here the design conditions to be fulfilled by a grating monochromator that does not increase the pulse duration significantly longer than the Fourier limit.

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Single-grating monochromator for extreme-ultraviolet ultrashort pulses

Cited by 156 publications

References 32 publications

Ultrafast momentum imaging of pseudospin-flip excitations in graphene

Ultrafast momentum imaging of pseudospin-flip excitations in graphene

A simple electron time-of-flight spectrometer for ultrafast vacuum ultraviolet photoelectron spectroscopy of liquid solutions

Design Study of Time-Preserving Grating Monochromators for Ultrashort Pulses in the Extreme-Ultraviolet and Soft X-Rays

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