scholarly journals Bound-State Electron Dynamics Driven by Near-Resonantly Detuned Intense and Ultrashort Pulsed XUV Fields

2020 ◽  
Vol 10 (18) ◽  
pp. 6153
Author(s):  
Alexander Magunia ◽  
Lennart Aufleger ◽  
Thomas Ding ◽  
Patrick Rupprecht ◽  
Marc Rebholz ◽  
...  
Keyword(s):  
Numerical Model ◽  
Electric Fields ◽  
Line Shape ◽  
Transient Absorption ◽  
Extreme Ultraviolet ◽  
Analytical Calculation ◽  
Underlying Mechanism ◽  
Bound State ◽  
Transient Absorption Spectrum ◽  
Autoionizing State

We report on numerical results revealing line-shape asymmetry changes of electronic transitions in atoms near-resonantly driven by intense extreme-ultraviolet (XUV) electric fields by monitoring their transient absorption spectrum after transmission through a moderately dense atomic medium. Our numerical model utilizes ultrashort broadband XUV laser pulses varied in their intensity (1014–1015 W/cm2) and detuning nearly out of resonance for a quantitative evaluation of the absorption line-shape asymmetry. It will be shown how transient energy shifts of the bound electronic states can be linked to these asymmetry changes in the case of an ultrashort XUV driving pulse temporally shorter than the lifetime of the resonant excitation, and how the asymmetry can be controlled by the near-resonant detuning of the XUV pulse. In the case of a two-level system, the numerical model is compared to an analytical calculation, which helps to uncover the underlying mechanism for the detuning- and intensity-induced line-shape modification and links it to the generalized Rabi frequency. To further apply the numerical model to recent experimental results of the near-resonant dressing of the 2s2p doubly excited state in helium by an ultrashort XUV free-electron laser pulse we extend the two-level model with an ionization continuum, thereby enabling the description of transmission-type (Fraunhofer-like) transient absorption of a strongly laser-coupled autoionizing state.

scholarly journals Line-shape broadening of an autoionizing state in helium at high XUV intensity

2021 ◽  
Author(s):  
Lennart Aufleger ◽  
Patrick Friebel ◽  
Patrick Rupprecht ◽  
Alexander Magunia ◽  
Thomas Ding ◽  
...  
Keyword(s):  
Excited State ◽  
Strong Coupling ◽  
Line Shape ◽  
Transient Absorption ◽  
Extreme Ultraviolet ◽  
Model Simulation ◽  
Transient Absorption Spectroscopy ◽  
Autoionizing State ◽  
Doubly Excited ◽  
Level Model

Abstract We study the interaction of intense extreme ultraviolet (XUV) light with the 2s2p doubly excited state in helium. In addition to previously understood energy-level and phase shifts, high XUV intensities may lead to other absorption line shape distortions. Here, we report on experimental transient-absorption spectroscopy results on the 2s2p line width modification in helium in intense stochastic XUV fields. A few-level model simulation is realized to investigate the origins of this effect. We find that the line shape broadening is connected to the strong coupling of the ground state to the 2s2p doubly excited state which is embedded in the ionization continuum. As the broadening takes place for intensities lower than for other strong-coupling processes, e.g. observing asymmetry changes of the absorption profile, this signature can be identified already in an intermediate intensity regime. These findings are in general relevant for resonant inner shell transitions in nonlinear experiments with XUV and x-ray photon energies at high intensity.

scholarly journals Measuring the frequency chirp of extreme-ultraviolet free-electron laser pulses by transient absorption spectroscopy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Thomas Ding ◽  
Marc Rebholz ◽  
Lennart Aufleger ◽  
Maximilian Hartmann ◽  
Veit Stooß ◽  
...  
Keyword(s):  
Free Electron ◽  
Free Electron Laser ◽  
Transient Absorption ◽  
Extreme Ultraviolet ◽  
Ultrashort Pulses ◽  
Laser Pulses ◽  
Transient Absorption Spectroscopy ◽  
Energy Structure ◽  
Frequency Chirp

AbstractHigh-intensity ultrashort pulses at extreme ultraviolet (XUV) and x-ray photon energies, delivered by state-of-the-art free-electron lasers (FELs), are revolutionizing the field of ultrafast spectroscopy. For crossing the next frontiers of research, precise, reliable and practical photonic tools for the spectro-temporal characterization of the pulses are becoming steadily more important. Here, we experimentally demonstrate a technique for the direct measurement of the frequency chirp of extreme-ultraviolet free-electron laser pulses based on fundamental nonlinear optics. It is implemented in XUV-only pump-probe transient-absorption geometry and provides in-situ information on the time-energy structure of FEL pulses. Using a rate-equation model for the time-dependent absorbance changes of an ionized neon target, we show how the frequency chirp can be directly extracted and quantified from measured data. Since the method does not rely on an additional external field, we expect a widespread implementation at FELs benefiting multiple science fields by in-situ on-target measurement and optimization of FEL-pulse properties.

Electrokinetic instability due to streamwise conductivity gradients in microchip electrophoresis

2021 ◽  
Vol 925 ◽  
Author(s):  
Kaushlendra Dubey ◽  
Sanjeev Sanghi ◽  
Amit Gupta ◽  
Supreet Singh Bahga
Keyword(s):  
Electric Field ◽  
Numerical Simulations ◽  
Electric Fields ◽  
Quantitative Measure ◽  
Underlying Mechanism ◽  
Scaling Analysis ◽  
Recirculating Flow ◽  
Electrokinetic Instability ◽  
Spatial Features ◽  
Proper Orthogonal Decomposition Technique

We present an experimental and numerical investigation of electrokinetic instability (EKI) in microchannel flow with streamwise conductivity gradients, such as those observed during sample stacking in capillary electrophoresis. A plug of a low-conductivity electrolyte solution is initially sandwiched between two high-conductivity zones in a microchannel. This spatial conductivity gradient is subjected to an external electric field applied along the microchannel axis, and for sufficiently strong electric fields an instability sets in. We have explored the physics of this EKI through experiments and numerical simulations, and supplemented the results using scaling analysis. We performed EKI experiments at different electric field values and visualised the flow using a passive fluorescent tracer. The experimental data were analysed using the proper orthogonal decomposition technique to obtain a quantitative measure of the threshold electric field for the onset of instability, along with the corresponding coherent structures. To elucidate the physical mechanism underlying the instability, we performed high-resolution numerical simulations of ion transport coupled with fluid flow driven by the electric body force. Simulations reveal that the non-uniform electroosmotic flow due to axially varying conductivity field causes a recirculating flow within the low-conductivity region, and creates a new configuration wherein the local conductivity gradients are orthogonal to the applied electric field. This configuration leads to EKI above a threshold electric field. The spatial features of the instability predicted by the simulations and the threshold electric field are in good agreement with the experimental observations and provide useful insight into the underlying mechanism of instability.

Ultrafast Triplet Generation at the Lead Halide Perovskite/Rubrene Interface

2021 ◽  
Author(s):  
Carl Conti ◽  
Alexander Bieber ◽  
Zachary VanOrman ◽  
Gregory Moller ◽  
Sarah Wieghold ◽  
...  
Keyword(s):  
Transient Absorption ◽  
Underlying Mechanism ◽  
Transient Absorption Spectroscopy ◽  
Trap States ◽  
Photovoltaic Devices ◽  
Data Points ◽  
Halide Perovskites ◽  
Absorption Features ◽  
Lead Halide ◽  
Visible Photon

Triplet sensitization of rubrene by bulk lead halide perovskites has recently resulted in efficient infrared-to-visible photon upconversion via triplet-triplet annihilation. Notably, this process occurrs under solar relavant fluxes, potentially paving the way toward integration with photovoltaic devices. In order to further improve the upconversion efficiency, the fundamental photophysical pathways at the perovskite/rubrene interface must be clearly understood to maximize charge extraction. Here, we utilize ultrafast transient absorption spectroscopy to elucidate the processes underlying the triplet generation at the perovskite/rubrene interface. Based on the bleach and photoinduced absorption features of the perovskite and perovskite/rubrene devices obtained at multiple pump wavelengths and fluences, along with their resultant kinetics, our results do not support charge transfer states or long-lived trap states as the underlying mechanism. Instead, the data points towards a triplet sensitization mechanism based on rapid extraction of thermally excited carriers on the picosecond timescale.

scholarly journals Tracking Intrinsic Properties of CH3NH3PbI3 Perovskite Thin Films Grown by Spin Coating Technique at Ambient Temperature

2019 ◽  
Vol 6 (2) ◽  
pp. 59-68
Author(s):  
Cliff Orori Mosiori ◽  
John Maera
Keyword(s):  
Thin Films ◽  
Optical Constants ◽  
Transient Absorption ◽  
Large Fraction ◽  
Perovskite Solar Cells ◽  
Transient Absorption Spectrum ◽  
Decay Kinetics ◽  
Lead Iodide ◽  
Time Resolved ◽  
Optoelectronic Applications

Methyl ammonium lead iodide has become a burgeoning class of hybrid halide perovskites of solution-processed semiconductors. Advancements in its processing and characterization underscore structural, optical, and electronic properties. They have led to the development of perovskite solar cells, photo detectors, lasers, and photo diodes with power conversion efficiencies mature to be classified as first and second-generation technologies. Characterizing forms an integral understanding the operating principles and fundamental limitations for optoelectronics applications. Studies outlined in this paper covers CH3NH3PbI3 using time-resolved pump-probe spectroscopy, X-ray diffractometry, spectrophotometry and other measurements. Thus this investigatiosn may serve as principle tool in analyzing excited state decay kinetics and optical nonlinearities in CH3NH3PbI3 thin films. It is demonstrated herein that non-resonant photoexcitation yields a large fraction of free carriers on a sub-picosecond time scale. If applied in practical optoelectronic applications then any photogenerated carriers may travel long carrier lengths before they are extracted to realize large external quantum efficiencies and efficient charge extraction. The optical constants of CH3NH3PbI3 are interpreted using ab initio calculations through models. Findings show good agreement between the optical constants derived from QSGW and those from related literature. Transition from the highest valence band (VB) to the lowest conduction band (CB) was found to be responsible for almost all the optical responses between 1.2 and 5.5 eV. It was concluded that optical constants and energy band diagrams of CH3NH3PbI3 can be used to simulate the contributions from different optical transitions to a typical transient absorption spectrum for many optoelectronic applications.

Thickness dependence of transient absorption spectrum for InGaN thin films

2003 ◽  
Vol 0 (7) ◽  
pp. 2606-2609
Author(s):  
M.-S. Nomura ◽  
M. Arita ◽  
S. Ashihara ◽  
S. Kako ◽  
M. Nishioka ◽  
...  
Keyword(s):  
Thin Films ◽  
Absorption Spectrum ◽  
Transient Absorption ◽  
Thickness Dependence ◽  
Transient Absorption Spectrum

scholarly journals Attosecond transient absorption spectrum of argon at the L2,3 edge

2018 ◽  
Vol 97 (3) ◽  
Author(s):  
Andrew Chew ◽  
Nicolas Douguet ◽  
Coleman Cariker ◽  
Jie Li ◽  
Eva Lindroth ◽  
...  
Keyword(s):  
Absorption Spectrum ◽  
Transient Absorption ◽  
Transient Absorption Spectrum

Clocking the buildup dynamics of light-induced states through attosecond transient absorption spectrum

2021 ◽  
Author(s):  
Xiaoxia Wu ◽  
Shaofeng Zhang ◽  
Difa Ye
Keyword(s):  
Floquet Theory ◽  
Transient Absorption ◽  
Scaling Law ◽  
Time Lag ◽  
Time Dependent ◽  
Transient Absorption Spectroscopy ◽  
Transient Absorption Spectrum ◽  
Wide Range ◽  
Maximal Shift ◽  
Buildup Time

Abstract The buildup processes of the light-induced states (LISs) in attosecond transient absorption spectroscopy are studied by solving the time-dependent Schrödinger equation and compared with the quasistatic Floquet theory, revealing a time lag of the maximal shift and strongest absorbance of the LIS with respect to the zero delay that is referred to as the buildup time. We analytically derive a scaling law for the buildup time that confirms the numerical results over a wide range of detunings. Our theory verifies the commonly accepted scenario of nearly instantaneous response of matter to light if the pump field is blue-detuned, but some differences are found in the near-resonant and red-detuning cases. Implications of the buildup time in petahertz optoelectronics are discussed.

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