HELIOS—A laboratory based on high-order harmonic generation of extreme ultraviolet photons for time-resolved spectroscopy

Plogmaker, Stefan; Terschlüsen, Joachim A.; Krebs, Nils; Svanqvist, Mattias; Forsberg, Johan; Cappel, Ute B.; Rubensson, Jan‐Erik; Siegbahn, Hans; Söderström, Johan

doi:10.1063/1.4937463

Cited by 25 publications

(16 citation statements)

References 41 publications

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“…This is achieved by performing a change of the employed laser technology, from a conventional titanium:sapphire laser to an optical parametric chirped pulse amplifier (OPCPA), entirely based on sub-picosecond ytterbium lasers 17 . The experimental apparatus presented in this work bridges the existing technology gap between widespread high-flux, high repetition rate sources with low photon energy 15,[18][19][20][21][22] and conventional high photon energy sources, based on high-order harmonic generation and operating at lower repetition rates [23][24][25][26][27][28][29][30][31] , thereby enabling a vast class of new experiments to be performed in the whole Brillouin zone of most materials. The structure of the paper is as follows: section II will be dedicated to the description of the light source, whereas the trARPES beamline will be described and characterized in section III.…”

Section: Introductionmentioning

confidence: 99%

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Puppin

Deng

Nicholson

et al. 2019

Review of Scientific Instruments

116

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Time-and angle-resolved photoemission spectroscopy (trARPES) employing a 500 kHz extreme-ultraviolet (XUV) light source operating at 21.7 eV probe photon energy is reported. Based on a high-power ytterbium laser, optical parametric chirped pulse amplification (OPCPA), and ultraviolet-driven high-harmonic generation, the light source produces an isolated high-harmonic with 110 meV bandwidth and a flux of more than 10 11 photons/second on the sample. Combined with a stateof-the-art ARPES chamber, this table-top experiment allows high-repetition rate pump-probe experiments of electron dynamics in occupied and normally unoccupied (excited) states in the entire Brillouin zone and with a temporal system response function below 40 fs. function A(k,ω) and a matrix element between the initial and final state |M k if | 2 ; here k and ω denote the electron's wavevector and angular frequency, respectively. Many-body effects are encoded in the spectral function A(k,ω) and manifest themselves in renormalization of the bare electronic bands and in the observed lineshape 1 . In a trARPES experiment, the distribution I(k,ω) is collected for a series of delays (τ ) between pump and probe pulses: after perturbation, the population distribution f(k,ω,τ ) evolves towards a quasi-thermal distribution and energetically relaxes on femto-to picosecond timescales 2 . During relaxation, the concomitant many-body interactions affect the transient spectral function A(k,ω,τ ) and even the photoemission matrix elements might change, if the final state's orbital symmetry is altered 3 . trARPES accesses at once the population dynamics, the evolution of the spectral function and the evolution of matrix elements. trARPES has found increasingly successful applications in the past few decades 4-6 : among many examples, trARPES was used to study photo-induced phase transitions 7-11 and to observe electronic states above the Fermi level, unoccupied under equilibrium conditions [12][13][14][15][16] . Energy conservation in the photoemission processes imposes that a femtosecond light source for trARPES must possess a photon energy ω ph exceeding the work function Φ, which in most materials lies in the range between 4 to 6 eV. Ultraviolet femtosecond light sources are thus required for these experiments.The conservation of the electrons' in-plane momentum ( k ) in the photoemission process allows reciprocal space resolution. The advantage of a probe with high photon energy is Journal of Electron Spectroscopy and Related Phenomena 200, 15 (2015). 79 SPECS Surface Nano Analysis GmbH, product spectrometer PHOIBOS TM 150 (2013), see

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Section: Introductionmentioning

confidence: 99%

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Puppin

Deng

Nicholson

et al. 2019

Review of Scientific Instruments

116

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“…Time resolved T-MOKE was performed at the HELIOS Laboratory, Uppsala University, Sweden. [24] A near-infrared (NIR) pump pulse of wave length 800 nm (1.5 eV) and pulse length 35 fs, and EUV probe pulse of energies ranging between 40 -70 eV and a pulse length of 20 fs are utilized in the T-MOKE-setup that measures the whole EUV spectra at once [12]. EUV photons are obtained via high harmonic generation with the same NIR pulse also used for pumping thus ensuring intrinsic synchronization.…”

Section: Experiments and Resultsmentioning

confidence: 99%

Experimental confirmation of the delayed Ni demagnetization in FeNi alloy

Jana

Knut

Muralidhar

et al. 2022

Applied Physics Letters

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Element-selective techniques are central for the understanding of ultrafast spin dynamics in multi-element materials, such as magnetic alloys. Recently, however, it turned out that the commonly used technique of the transverse magneto-optical Kerr effect (T-MOKE) in the extreme ultraviolet range may have issues with unwanted crosstalk between different elemental signals and energy-dependent non-linear response. This problem can be sizeable, which puts recent observations of ultrafast spin transfer from Fe to Ni sites in FeNi alloys into question. In this study, we investigate the Fe-to-Ni spin transfer in a crosstalk-free time-resolved x-ray magnetic circular dichroism (XMCD) experiment with a reliable time reference. With XMCD near the absorption maxima, we find a very similar Fe and Ni dynamics as with T-MOKE from identical samples. Considering the potential non-linearities of the T-MOKE response, such a good agreement in our findings is remarkable. Our data provide the ongoing discussion about ultrafast spin-transfer mechanisms in FeNi systems with a broader experimental basis.

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“…The near-infrared (NIR) pump pulse has a wavelength of ∼ 800 nm (∼ 1.5 eV) and a pulse length of ∼ 35 fs. The broadband EUV probe pulse has energies between 40 − 72 eV and a pulse length of ∼ 20 fs [45][46][47]. Since the NIR pump and the EUV pulse are generated from the same laser pulse, the temporal jitter between the NIR and EUV is eliminated and hence the temporal resolution is determined by the pulse widths.…”

Section: Experiments Experimental Setupmentioning

confidence: 99%

Analysis of the linear relationship between asymmetry and magnetic moment at the M edge of 3d transition metals

Jana¹,

Malik²,

Kvashnin³

et al. 2020

Phys. Rev. Research

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The magneto-optical response of Fe and Ni during ultrafast demagnetization is studied experimentally and theoretically. We have performed pump-probe experiments in the transverse magnetooptical Kerr effect (T-MOKE) geometry using photon energies that cover the M-absorption edges of Fe and Ni between 40 to 72 eV. The asymmetry was detected by measuring the reflection of light for two different orientations of the sample magnetization. Density functional theory (DFT) was used to calculate the magneto-optical response of different magnetic configurations, representing different types of excitations: long-wavelength magnons, short wavelength magnons, and Stoner excitations. In the case of Fe, we find that the calculated asymmetry is strongly dependent on the specific type of magnetic excitation. Our modelling also reveals that during remagnetization Fe is, to a reasonable approximation, described by magnons, even though small non-linear contributions could indicate some degree of Stoner excitations as well. In contrast, we find that the calculated asymmetry in Ni is rather insensitive to the type of magnetic excitations. However, there is a weak non-linearity in the relation between asymmetry and the off-diagonal component of the dielectric tensor, which does not originate from the modifications of the electronic structure. Our experimental and theoretical results thus emphasize the need of considering a coupling between asymmetry and magnetization that may be more complex that a simple linear relationship. This insight is crucial for the microscopic interpretation of ultrafast magnetization experiments.

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HELIOS—A laboratory based on high-order harmonic generation of extreme ultraviolet photons for time-resolved spectroscopy

Cited by 25 publications

References 41 publications

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Experimental confirmation of the delayed Ni demagnetization in FeNi alloy

Analysis of the linear relationship between asymmetry and magnetic moment at the M edge of 3d transition metals

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