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Di Palo N, Adamska L, Bonetti S, Inzani G, Talarico M, Arias Velasco M, Dolso GL, Borrego-Varillas R, Nisoli M, Pittalis S, Rozzi CA, Lucchini M. Role of crystal orientation in attosecond photoinjection dynamics of germanium. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2024; 11:044303. [PMID: 39175799 PMCID: PMC11341128 DOI: 10.1063/4.0000253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/16/2024] [Accepted: 07/30/2024] [Indexed: 08/24/2024]
Abstract
Understanding photoinjection in semiconductors-a fundamental physical process-represents the first step toward devising new opto-electronic devices, capable of operating on unprecedented time scales. Fostered by the development of few-femtosecond, intense infrared pulses, and attosecond spectroscopy techniques, ultrafast charge injection in solids has been the subject of intense theoretical and experimental investigation. Recent results have shown that while under certain conditions photoinjection can be ascribed to a single, well-defined phenomenon, in a realistic multi-band semiconductor like Ge, several competing mechanisms determine the sub-cycle interaction of an intense light field with the atomic and electronic structure of matter. In this latter case, it is yet unclear how the complex balance between the different physical mechanisms is altered by the chosen interaction geometry, dictated by the relative orientation between the crystal lattice and the laser electric field direction. In this work, we investigate ultrafast photoinjection in a Ge monocrystalline sample with attosecond temporal resolution under two distinct orientations. Our combined theoretical and experimental effort suggests that the physical mechanisms determining carrier excitation in Ge are largely robust against crystal rotation. Nevertheless, the different alignment between the laser field and the crystal unit cell causes non-negligible changes in the momentum distribution of the excited carriers and their injection yield. Further experiments are needed to clarify whether the crystal orientation can be used to tune the photoinjection of carriers in a semiconductor at these extreme time scales.
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Affiliation(s)
- Nicola Di Palo
- Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci, 20133 Milano, Italy
| | | | - Simone Bonetti
- Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci, 20133 Milano, Italy
| | - Giacomo Inzani
- Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci, 20133 Milano, Italy
| | - Matteo Talarico
- Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci, 20133 Milano, Italy
| | | | - Gian Luca Dolso
- Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci, 20133 Milano, Italy
| | | | | | - Stefano Pittalis
- CNR – Istituto Nanoscienze, via Campi 213/A, I-41125 Modena, Italy
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2
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Leone SR. Reinvented: An Attosecond Chemist. Annu Rev Phys Chem 2024; 75:1-19. [PMID: 38012050 DOI: 10.1146/annurev-physchem-083122-011610] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
Attosecond science requires a substantial rethinking of how to make measurements on very short timescales; how to acquire the necessary equipment, technology, and personnel; and how to build a set of laboratories for such experiments. This entails a rejuvenation of the author in many respects, in the laboratory itself, with regard to students and postdocs, and in generating funding for research. It also brings up questions of what it means to do attosecond science, and the discovery of the power of X-ray spectroscopy itself, which complements the short timescales addressed. The lessons learned, expressed in the meanderings of this autobiographical article, may be of benefit to others who try to reinvent themselves.
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Affiliation(s)
- Stephen R Leone
- Departments of Chemistry and Physics and Lawrence Berkeley National Laboratory, University of California, Berkeley, California, USA;
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3
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Kretschmar M, Svirplys E, Volkov M, Witting T, Nagy T, Vrakking MJJ, Schütte B. Compact realization of all-attosecond pump-probe spectroscopy. SCIENCE ADVANCES 2024; 10:eadk9605. [PMID: 38381830 PMCID: PMC10881040 DOI: 10.1126/sciadv.adk9605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 01/17/2024] [Indexed: 02/23/2024]
Abstract
The ability to perform attosecond-pump attosecond-probe spectroscopy (APAPS) is a longstanding goal in ultrafast science. While first pioneering experiments demonstrated the feasibility of APAPS, the low repetition rates (10 to 120 Hz) and the large footprints of existing setups have so far hindered the widespread exploitation of APAPS. Here, we demonstrate two-color APAPS using a commercial laser system at 1 kHz, straightforward post-compression in a hollow-core fiber, and a compact high-harmonic generation (HHG) setup. The latter enables the generation of intense extreme-ultraviolet (XUV) pulses by using an out-of-focus HHG geometry and by exploiting a transient blueshift of the driving laser in the HHG medium. Near-isolated attosecond pulses are generated, as demonstrated by one-color and two-color XUV-pump XUV-probe experiments. Our concept allows selective pumping and probing on extremely short timescales in many laboratories and permits investigations of fundamental processes that are not accessible by other pump-probe techniques.
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Affiliation(s)
| | | | - Mikhail Volkov
- Max-Born-Institut, Max-Born-Strasse 2A, 12489 Berlin, Germany
| | - Tobias Witting
- Max-Born-Institut, Max-Born-Strasse 2A, 12489 Berlin, Germany
| | - Tamás Nagy
- Max-Born-Institut, Max-Born-Strasse 2A, 12489 Berlin, Germany
| | | | - Bernd Schütte
- Max-Born-Institut, Max-Born-Strasse 2A, 12489 Berlin, Germany
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4
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Hansen T, Bezriadina T, Popova-Gorelova D. Theoretical Description of Attosecond X-ray Absorption Spectroscopy of Frenkel Exciton Dynamics. Molecules 2023; 28:molecules28114502. [PMID: 37298978 DOI: 10.3390/molecules28114502] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Revised: 05/26/2023] [Accepted: 05/29/2023] [Indexed: 06/12/2023] Open
Abstract
Frenkel excitons are responsible for the transport of light energy in many molecular systems. Coherent electron dynamics govern the initial stage of Frenkel-exciton transfer. Capability to follow coherent exciton dynamics in real time will help to reveal their actual contribution to the efficiency of light-harvesting. Attosecond X-ray pulses are the tool with the necessary temporal resolution to resolve pure electronic processes with atomic sensitivity. We describe how attosecond X-ray pulses can probe coherent electronic processes during Frenkel-exciton transport in molecular aggregates. We analyze time-resolved absorption cross section taking broad spectral bandwidth of an attosecond pulse into account. We demonstrate that attosecond X-ray absorption spectra can reveal delocalization degree of coherent exciton transfer dynamics.
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Affiliation(s)
- Tim Hansen
- I. Institute for Theoretical Physics, Universität Hamburg, Notkestr. 9, 22607 Hamburg, Germany
| | - Tatiana Bezriadina
- I. Institute for Theoretical Physics, Universität Hamburg, Notkestr. 9, 22607 Hamburg, Germany
- Centre for Ultrafast Imaging, Luruper Chaussee 149, 22671 Hamburg, Germany
| | - Daria Popova-Gorelova
- I. Institute for Theoretical Physics, Universität Hamburg, Notkestr. 9, 22607 Hamburg, Germany
- Centre for Ultrafast Imaging, Luruper Chaussee 149, 22671 Hamburg, Germany
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5
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Kobayashi Y, Leone SR. Characterizing coherences in chemical dynamics with attosecond time-resolved x-ray absorption spectroscopy. J Chem Phys 2022; 157:180901. [DOI: 10.1063/5.0119942] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Coherence can drive wave-like motion of electrons and nuclei in photoexcited systems, which can yield fast and efficient ways to exert materials’ functionalities beyond the thermodynamic limit. The search for coherent phenomena has been a central topic in chemical physics although their direct characterization is often elusive. Here, we highlight recent advances in time-resolved x-ray absorption spectroscopy (tr-XAS) to investigate coherent phenomena, especially those that utilize the eminent light source of isolated attosecond pulses. The unparalleled time and state sensitivities of tr-XAS in tandem with the unique element specificity render the method suitable to study valence electronic dynamics in a wide variety of materials. The latest studies have demonstrated the capabilities of tr-XAS to characterize coupled electronic–structural coherence in small molecules and coherent light–matter interactions of core-excited excitons in solids. We address current opportunities and challenges in the exploration of coherent phenomena, with potential applications for energy- and bio-related systems, potential crossings, strongly driven solids, and quantum materials. With the ongoing developments in both theory and light sources, tr-XAS holds great promise for revealing the role of coherences in chemical dynamics.
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Affiliation(s)
- Yuki Kobayashi
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - Stephen R. Leone
- Department of Chemistry, University of California, Berkeley, California 94720, USA
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Physics, University of California, Berkeley, California 94720, USA
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6
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Abel JJ, Wiesner F, Nathanael J, Reinhard J, Wünsche M, Schmidl G, Gawlik A, Hübner U, Plentz J, Rödel C, Paulus GG, Fuchs S. Absolute EUV reflectivity measurements using a broadband high-harmonic source and an in situ single exposure reference scheme. OPTICS EXPRESS 2022; 30:35671-35683. [PMID: 36258513 DOI: 10.1364/oe.463216] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Accepted: 08/02/2022] [Indexed: 06/16/2023]
Abstract
We present a tabletop setup for extreme ultraviolet (EUV) reflection spectroscopy in the spectral range from 40 to 100 eV by using high-harmonic radiation. The simultaneous measurements of reference and sample spectra with high energy resolution provide precise and robust absolute reflectivity measurements, even when operating with spectrally fluctuating EUV sources. The stability and sensitivity of EUV reflectivity measurements are crucial factors for many applications in attosecond science, EUV spectroscopy, and nano-scale tomography. We show that the accuracy and stability of our in situ referencing scheme are almost one order of magnitude better in comparison to subsequent reference measurements. We demonstrate the performance of the setup by reflective near-edge x-ray absorption fine structure measurements of the aluminum L2/3 absorption edge in α-Al2O3 and compare the results to synchrotron measurements.
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7
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Tsai MS, Liang AY, Tsai CL, Lai PW, Lin MW, Chen MC. Nonlinear compression toward high-energy single-cycle pulses by cascaded focus and compression. SCIENCE ADVANCES 2022; 8:eabo1945. [PMID: 35921417 PMCID: PMC9348793 DOI: 10.1126/sciadv.abo1945] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Accepted: 06/21/2022] [Indexed: 05/31/2023]
Abstract
The advancement of contemporary ultrafast science requires reliable sources to provide high-energy few-cycle light pulses. Through experiments and simulations, we demonstrate an arrangement of pulse postcompression, referred to as cascaded focus and compression (CASCADE), for generating millijoule-level, single-cycle pulses in a compact fashion. CASCADE is realized by a series of foci in matter, whereas pulse compression is provided immediately after each focus to maintain a high efficiency of spectral broadening. By implementing four stages of CASCADE in argon cells, we achieve 50-fold compression of millijoule-level pulses at 1030 nanometers from 157 to 3.1 femtoseconds, with an output pulse energy of 0.98 millijoules and a transmission efficiency of 73%. When driving high harmonic generation, these single-cycle pulses enable the creation of a carrier-envelope phase-dependent extreme ultraviolet continuum with energies extending up to 180 electron volts, providing isolated attosecond pulses at the output.
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Affiliation(s)
- Ming-Shian Tsai
- Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 300044, Taiwan
| | - An-Yuan Liang
- Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 300044, Taiwan
| | - Chia-Lun Tsai
- Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 300044, Taiwan
| | - Po-Wei Lai
- Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu 300044, Taiwan
| | - Ming-Wei Lin
- Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu 300044, Taiwan
| | - Ming-Chang Chen
- Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 300044, Taiwan
- Department of Physics, National Tsing Hua University, Hsinchu 300044, Taiwan
- Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu, Taiwan
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8
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Borrego-Varillas R, Lucchini M, Nisoli M. Attosecond spectroscopy for the investigation of ultrafast dynamics in atomic, molecular and solid-state physics. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2022; 85:066401. [PMID: 35294930 DOI: 10.1088/1361-6633/ac5e7f] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Accepted: 03/16/2022] [Indexed: 06/14/2023]
Abstract
Since the first demonstration of the generation of attosecond pulses (1 as = 10-18s) in the extreme-ultraviolet spectral region, several measurement techniques have been introduced, at the beginning for the temporal characterization of the pulses, and immediately after for the investigation of electronic and nuclear ultrafast dynamics in atoms, molecules and solids with unprecedented temporal resolution. The attosecond spectroscopic tools established in the last two decades, together with the development of sophisticated theoretical methods for the interpretation of the experimental outcomes, allowed to unravel and investigate physical processes never observed before, such as the delay in photoemission from atoms and solids, the motion of electrons in molecules after prompt ionization which precede any notable nuclear motion, the temporal evolution of the tunneling process in dielectrics, and many others. This review focused on applications of attosecond techniques to the investigation of ultrafast processes in atoms, molecules and solids. Thanks to the introduction and ongoing developments of new spectroscopic techniques, the attosecond science is rapidly moving towards the investigation, understanding and control of coupled electron-nuclear dynamics in increasingly complex systems, with ever more accurate and complete investigation techniques. Here we will review the most common techniques presenting the latest results in atoms, molecules and solids.
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Affiliation(s)
- Rocío Borrego-Varillas
- Institute for Photonics and Nanotechnologies (IFN), Consiglio Nazionale delle Ricerche (CNR), Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - Matteo Lucchini
- Institute for Photonics and Nanotechnologies (IFN), Consiglio Nazionale delle Ricerche (CNR), Piazza Leonardo da Vinci 32, 20133 Milano, Italy
- Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - Mauro Nisoli
- Institute for Photonics and Nanotechnologies (IFN), Consiglio Nazionale delle Ricerche (CNR), Piazza Leonardo da Vinci 32, 20133 Milano, Italy
- Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
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9
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Dolso GL, Moio B, Inzani G, Di Palo N, Sato SA, Borrego-Varillas R, Nisoli M, Lucchini M. Reconstruction of ultrafast exciton dynamics with a phase-retrieval algorithm. OPTICS EXPRESS 2022; 30:12248-12267. [PMID: 35472864 DOI: 10.1364/oe.451759] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Accepted: 03/04/2022] [Indexed: 06/14/2023]
Abstract
The first step to gain optical control over the ultrafast processes initiated by light in solids is a correct identification of the physical mechanisms at play. Among them, exciton formation has been identified as a crucial phenomenon which deeply affects the electro-optical properties of most semiconductors and insulators of technological interest. While recent experiments based on attosecond spectroscopy techniques have demonstrated the possibility to observe the early-stage exciton dynamics, the description of the underlying exciton properties remains non-trivial. In this work we propose a new method called extended Ptychographic Iterative engine for eXcitons (ePIX), capable of reconstructing the main physical properties which determine the evolution of the quasi-particle with no prior knowledge of the exact relaxation dynamics or the pump temporal characteristics. By demonstrating its accuracy even when the exciton dynamics is comparable to the pump pulse duration, ePIX is established as a powerful approach to widen our knowledge of solid-state physics.
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10
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11
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Lucchini M, Sato SA, Lucarelli GD, Moio B, Inzani G, Borrego-Varillas R, Frassetto F, Poletto L, Hübener H, De Giovannini U, Rubio A, Nisoli M. Unravelling the intertwined atomic and bulk nature of localised excitons by attosecond spectroscopy. Nat Commun 2021; 12:1021. [PMID: 33589638 PMCID: PMC7884782 DOI: 10.1038/s41467-021-21345-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Accepted: 01/25/2021] [Indexed: 11/09/2022] Open
Abstract
The electro-optical properties of most semiconductors and insulators of technological interest are dominated by the presence of electron-hole quasi-particles, called excitons. The manipulation of excitons in dielectrics has recently received great attention, with possible applications in different fields including optoelectronics and photonics. Here, we apply attosecond transient reflection spectroscopy in a sequential two-foci geometry and observe sub-femtosecond dynamics of a core-level exciton in bulk MgF2 single crystals. Furthermore, we access absolute phase delays, which allow for an unambiguous comparison with theoretical calculations. Our results show that excitons surprisingly exhibit a dual atomic- and solid-like character, which manifests itself on different time scales. While the former is responsible for a femtosecond optical Stark effect, the latter dominates the attosecond excitonic response. Further theoretical investigation reveals a link with the exciton sub-femtosecond nanometric motion and allows us to envision a new route to control exciton dynamics in the close-to-petahertz regime.
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Affiliation(s)
- Matteo Lucchini
- Department of Physics, Politecnico di Milano, 20133, Milano, Italy. .,Institute for Photonics and Nanotechnologies, IFN-CNR, 20133, Milano, Italy.
| | - Shunsuke A Sato
- Center for Computational Sciences, University of Tsukuba, Tsukuba, 305-8577, Japan.,Max Planck Institute for the Structure and Dynamics of Matter, 22761, Hamburg, Germany
| | - Giacinto D Lucarelli
- Department of Physics, Politecnico di Milano, 20133, Milano, Italy.,Institute for Photonics and Nanotechnologies, IFN-CNR, 20133, Milano, Italy
| | - Bruno Moio
- Department of Physics, Politecnico di Milano, 20133, Milano, Italy
| | - Giacomo Inzani
- Department of Physics, Politecnico di Milano, 20133, Milano, Italy
| | | | - Fabio Frassetto
- Institute for Photonics and Nanotechnologies, IFN-CNR, 35131, Padova, Italy
| | - Luca Poletto
- Institute for Photonics and Nanotechnologies, IFN-CNR, 35131, Padova, Italy
| | - Hannes Hübener
- Max Planck Institute for the Structure and Dynamics of Matter, 22761, Hamburg, Germany
| | - Umberto De Giovannini
- Max Planck Institute for the Structure and Dynamics of Matter, 22761, Hamburg, Germany.,Nano-Bio Spectroscopy Group, Universidad del País Vasco, 20018, San Sebastian, Spain
| | - Angel Rubio
- Max Planck Institute for the Structure and Dynamics of Matter, 22761, Hamburg, Germany.,Nano-Bio Spectroscopy Group, Universidad del País Vasco, 20018, San Sebastian, Spain
| | - Mauro Nisoli
- Department of Physics, Politecnico di Milano, 20133, Milano, Italy.,Institute for Photonics and Nanotechnologies, IFN-CNR, 20133, Milano, Italy
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12
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Géneaux R, Chang HT, Schwartzberg AM, Marroux HJB. Source noise suppression in attosecond transient absorption spectroscopy by edge-pixel referencing. OPTICS EXPRESS 2021; 29:951-960. [PMID: 33726320 DOI: 10.1364/oe.412117] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Accepted: 12/01/2020] [Indexed: 06/12/2023]
Abstract
Attosecond transient absorption spectroscopy (ATAS) is used to observe photoexcited dynamics with outstanding time resolution. The main experimental challenge of this technique is that high-harmonic generation sources show significant instabilities, resulting in sub-par sensitivity when compared to other techniques. This paper proposes edge-pixel referencing as a means to suppress this noise. Two approaches are introduced: the first is deterministic and uses a correlation analysis, while the second relies on singular value decomposition. Each method is demonstrated and quantified on a noisy measurement taken on WS2 and results in a fivefold increase in sensitivity. The combination of the two methods ensures the fidelity of the procedure and can be implemented on live data collection but also on existing datasets. The results show that edge-referencing methods bring the sensitivity of ATAS near the detector noise floor. An implementation of the post-processing code is provided to the reader.
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13
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Dolso GL, Moio B, Inzani G, Di Palo N, Borrego-Varillas R, Nisoli M, Lucchini M. Ultrafast exciton dynamics reconstruction with a ptychographic approach. EPJ WEB OF CONFERENCES 2021. [DOI: 10.1051/epjconf/202125513005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Excitons characterize the ultrafast response of many materials of technological interest. While the development of attosecond science has unlocked the possibility of performing experiments with a suitable timeresolution, the access to the exciton properties remains a non-trivial step. We propose therefore a novel approach to disclose the physical properties behind the ultrafast exciton dynamics based on a phase-retrieval method.
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14
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Chen M, Lopata K. First-Principles Simulations of X-ray Transient Absorption for Probing Attosecond Electron Dynamics. J Chem Theory Comput 2020; 16:4470-4478. [PMID: 32470295 PMCID: PMC7467644 DOI: 10.1021/acs.jctc.0c00122] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
X-ray transient absorption spectroscopy (XTAS) is a promising technique for measuring electron dynamics in molecules and solids with attosecond time resolutions. In XTAS, the elemental specificity and spatial locality of core-to-valence X-ray absorption is exploited to relate modulations in the time-resolved absorption spectra to local electron density variations around particular atoms. However, interpreting these absorption modulations and frequency shifts as a function of the time delay in terms of dynamics can be challenging. In this paper, we present a first-principles study of attosecond XTAS in a selection of simple molecules based on real-time time-dependent density functional theory (RT-TDDFT) with constrained DFT to emulate the state of the system following the interaction with a ultraviolet pump laser. In general, there is a decrease in the optical density and a blue shift in the frequency with increasing electron density around the absorbing atom. In carbon monoxide (CO), modulations in the O K-edge occur at the frequency of the valence electron dynamics, while for dioxygen (O2) they occur at twice the frequency, due to the indistinguishability of the oxygen atoms. In 4-aminophenol (H2NC6H4OH), likewise, there is a decrease in the optical density and a blue shift in the frequency for the oxygen and nitrogen K-edges with increasing charge density on the O and N, respectively. Similar effects are observed in the nitrogen K-edge for a long-range charge-transfer excitation in a benzene (C6H6)-tetracyanoethylene (C6N4; TCNE) dimer but with weaker modulations due to the delocalization of the charge across the entire TCNE molecule. Additionally, in all cases, there are pre-edge features corresponding to core transitions to depopulated orbitals. These potentially offer a background-free signal that only appears in pumped molecules.
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Affiliation(s)
- Min Chen
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Kenneth Lopata
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States.,Center for Computation and Technology, Louisiana State University, Baton Rouge, Louisiana 70803, United States
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