Find Academic Supervisors

• X-ray Physics
• Synchrotron Radiation
• Medical Imaging
• +5 more

Benedikt Günther is a research scientist at the Technical University of Munich (TUM) working within the Chair of Biomedical Physics led by Prof. Dr. Franz Pfeiffer. His research focuses on the Munich Compact Light Source (MuCLS), a laboratory-scale inverse Compton X-ray source that provides synchrotron-like radiation for biomedical applications. Günther plays a key role in developing, optimizing, and characterizing this innovative technology, contributing to both its fundamental physics and practical medical applications. His primary research interests center around X-ray physics and imaging techniques, particularly laser enhancement cavities for inverse Compton X-ray sources, X-ray microscopy, dynamic phase-contrast imaging, and X-ray spectroscopy. Günther's work bridges fundamental physics with practical medical applications, developing instrumentation that brings synchrotron-quality imaging to conventional laboratory settings. His research has significant implications for improving medical diagnostics while making advanced imaging techniques more accessible. Analysis of Günther's publication record reveals a consistent focus on advancing compact X-ray source technology and its applications. His work demonstrates expertise in both theoretical modeling and experimental implementation, with publications spanning instrument development, imaging techniques, and specific medical applications. The research shows progression from fundamental source characterization to increasingly sophisticated biomedical applications, particularly in breast imaging, dental diagnostics, and materials science. 2019 Best Poster Award at the combined meeting of the 68th Denver X-ray Conference (DXC) & 25th International Congress on X-ray Optics and Microanalysis (ICXOM) for 'Full-Field Structured Illumination Super-Resolution X-ray Transmission Microscopy' Günther regularly presents his work at major international conferences including the International Particle Accelerator Conference, High-Brightness Sources and Light-driven Interactions Congress, and specialized X-ray imaging meetings. His research is conducted within the Munich Compact Light Source facility, a collaborative project involving physicists, engineers, and medical researchers working to develop laboratory-scale synchrotron technology for widespread biomedical use.

Ioachim PupezaView profile

Professor

• Optical Spectroscopy
• Field-Resolved Spectroscopy
• Precision Optical Measurements
• +6 more

Prof. Dr. Ioachim Pupeza serves as Group Leader in the Department of Spectroscopy/Imaging at the Leibniz Institute of Photonic Technology (Leibniz-IPHT) in Jena, Germany. His research focuses on advanced optical measurement techniques, particularly in the field of field-resolved spectroscopy and precision optical measurements. Dr. Pupeza's research interests center around optical spectroscopy with a particular emphasis on field-resolved techniques that capture the complete electric field waveform of light-matter interactions. His work spans infrared spectroscopy , molecular fingerprinting , ultrafast laser technology , and precision optical measurements . He has made significant contributions to electro-optic sampling techniques, which enable characterization of electric-field waveforms across the terahertz to visible spectral range. His research also extends to mid-infrared light generation , terahertz spintronic emitters , and cavity-enhanced spectroscopy , with applications ranging from fundamental physics to medical diagnostics. Analysis of Dr. Pupeza's recent publications reveals a strong trend toward increasingly sophisticated field-resolved spectroscopy techniques with applications in both fundamental science and practical diagnostics. His work has evolved from basic measurement techniques to applications in cancer detection through molecular fingerprinting of biofluids. A consistent theme across his publications is the pursuit of higher precision, broader bandwidth, and improved sensitivity in optical measurements, often achieving attosecond-level precision. His research bridges physics, engineering, and medical applications, demonstrating how fundamental optical advances can translate to real-world diagnostic tools. Dr. Pupeza leads the research group "Field-Resolved Optical Precision Measurement Methods" at Leibniz-IPHT, which appears to collaborate extensively with other research institutions and groups. His work involves sophisticated laser systems including high-power Yb:YAG thin-disk oscillators, femtosecond enhancement cavities, and dual-oscillator systems for precision measurements. The group's research has implications for molecular spectroscopy, medical diagnostics, and fundamental studies of light-matter interactions at the most fundamental time scales.

Alexandre Mermillod-BlondinView profile

Researcher

• Laser-Matter Interaction
• Ultrafast Optics
• Photonic Structures
• +1 more

Dr. Alexandre Mermillod-Blondin is a Principal Investigator heading a DFG-funded project on 'Micromachining with few-cycle pulses' at the Max Born Institute. His research focuses on fundamental laser-matter interactions and direct laser writing of 3D micro-optical systems in transparent materials. Key investigations include plasma formation mechanisms in dielectrics, relaxation dynamics, and applications in photonic device fabrication. His group utilizes phase-contrast microscopy and time-resolved techniques to characterize ultrafast processes.

Michael Horn-von HoegenView profile

Professor

• Surface Physics
• Ultrafast Dynamics
• Electron Diffraction
• +4 more

Prof. Dr. Michael Horn-von Hoegen is a full professor in the Faculty of Physics at the University of Duisburg-Essen , Germany. His research focuses on ultrafast structural dynamics , surface physics , and 2D materials , particularly using electron diffraction and plasmonic imaging techniques. He leads the Horn-von Hoegen Group , which plays a central role in the Collaborative Research Center CRC 1242 Non-Equilibrium Dynamics of Condensed Matter in the Time Domain , where his team investigates driven phase transitions and phonon systems with sub-femtosecond temporal resolution. Location: Office Window MF260, Faculty of Physics, Lotharstr. 1-21, 47057 Duisburg Contact: Tel. +49 (203) 379 1439 | Fax +49 (203) 379 1555 His research spans ultrafast electron diffraction of photo-induced phase transitions in atomic wires and topological materials , with recent breakthroughs on Kibble-Zurek dynamics in the Si(001) surface and chiral plasmon polaritons . The group’s 15 most recent publications (2025-2022) address phenomena such as negative thermal expansion in 2D materials , electron-phonon coupling in Pb/Si heterostructures , and quantum pathway analysis in Bismuth films . These works are categorized under disciplines like Condensed Matter Physics , Nanooptics , and Ultrafast Dynamics , with subfields including Ising Model Transitions , Plasmon Focusing , and Time-Resolved Diffraction . Prof. Horn-von Hoegen serves as DFG Liaison Officer for the University of Duisburg-Essen, providing guidance on Deutsche Forschungsgemeinschaft (DFG) proposals . His group has mentored notable researchers including Dr. Simon Sindermann (postdoc at IBM), Dr. Anja Hanisch-Blicharski (Leopoldina Fellow), Dr. Hichem Hattab (Leopoldina Fellowship), and Dr. Marin Petrovic (Humboldt Fellow). The group’s laboratory facilities include advanced ultrafast electron diffraction and photoemission microscopy systems, enabling studies of atomic-scale processes such as molecular dynamics simulations of laser-excited surfaces and domain wall motion in Si(553)-Au systems .

Elena del ValleView profile

Research Professor

• Quantum Optics
• Cavity-QED
• Light-Matter Interaction
• +2 more

Elena del Valle is a Research Professor at the Technical University of Munich and Universidad Autónoma de Madrid, specializing in Theoretical Condensed Matter Physics. As a Hans Fischer Fellow at TUM-IAS, her research focuses on quantum optics, light-matter interactions, and nanophotonics. Her work explores quantum light generation, including single-photon sources, N-photon bundles, and quantum correlations in cavity-QED systems. She investigates fundamental phenomena such as photon statistics, entanglement, and polariton dynamics in semiconductor nanostructures. Del Valle's research demonstrates strong trends in quantum emitter technologies and nanophotonic device applications, with publications frequently appearing in high-impact journals like Nature Photonics and Physical Review Letters. Her contributions advance quantum communication, sensing, and computing platforms. She has received numerous awards including the Excellence Award for University Professors (2020), Ramón y Cajal award (2014), and Humboldt Research Fellowship (2011). She supervises research in quantum optics and mentors students in nanophotonics. As Principal Investigator of multiple projects, she leads the 'Novel quantum-light sources' focus group at TUM-IAS, collaborating with experimental groups to develop next-generation quantum technologies.

Cedrik MeierView profile

Professor

• Nanophotonics
• Plasmonics
• Metamaterials
• +3 more

Prof. Dr. Cedrik Meier is a faculty member at the University of Paderborn , affiliated with the Faculty of Natural Sciences and serving as the head of the Department of Physics . He holds the academic rank of Professor and chairs the Audit Committee. Education: Diplom in Physik, Ruhr-Universität Bochum (1998) Dr. rer. nat. in Experimentalphysik, Ruhr-Universität Bochum (2001) Habilitation, Universität Duisburg-Essen (2007) His research focuses on Nanophotonics , Plasmonics , Metamaterials , and Nonlinear Optics . The work involves developing novel photonic devices using nanofabrication techniques and materials like zinc oxide (ZnO) and silicon metasurfaces . Recent publications highlight advancements in third harmonic generation , correlated photon sources , and nonlinear optical effects in nanostructured materials. Key projects include TRR 142 (Tailor-Made Nonlinear Photonics) and studies on quantum dot positioning and liquid crystal-tunable devices . Scientific Awards: Golden Chalk for teaching physics (2016) Junge Kolleg, NRW Academy of Sciences (2007) Gottschalk-Diederich Baedeker Prize (2007) NanoFutur Award (2006) DFG Postdoc Fellowship (2003) Evangelical Study Association Villigst Scholarship (1998) He has led research groups at multiple institutions and currently oversees the Nanophotonics & Nanomaterials working group. His teaching includes Experimental Physics D and Lab Projects .

• Radiochemistry
• Radioecology
• Actinide Chemistry
• +7 more

Thorsten Stumpf is a Professor and Director of the Institute of Resource Ecology at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), with a joint professorship in Radiochemistry/Radioecology at Technische Universität Dresden. His work bridges fundamental chemistry and environmental safety in nuclear waste management. Research Interests: His research focuses on the molecular-level understanding of actinide and radionuclide behavior in the environment, including speciation, migration, and interaction with minerals, organic matter, and microorganisms. Key areas include radiochemistry, geochemistry, environmental chemistry, and nuclear waste disposal science. The recent publications reflect a strong trend in using advanced spectroscopic and synchrotron techniques (e.g., TRLFS, EXAFS, XRD) to study actinide speciation and redox behavior. Themes include bioassociation of radionuclides with plants and fungi, formation of actinide nanoparticles, and molecular interactions at mineral-water interfaces—critical for deep geological repository safety assessments. Scientific Awards: Fritz-Straßmann-Preis of the GDCh 'Fachgruppe Nuklearchemie' (2013) Advising and Grants: He has led significant research initiatives, including the Helmholtz-University Young Investigator Group and the Virtual Institute 'Advanced Solid – Aqueous Radiogeochemistry'. While specific students are not listed, his extensive publication record with multiple co-authors suggests active mentoring. His work is supported by Helmholtz Association funding and strategic collaborations. Labs and Teams: He leads the Institute of Resource Ecology at HZDR, which houses advanced laboratories for radiochemistry, spectroscopy, and environmental simulation. The institute is part of a larger network including CASUS and the Dresden High Magnetic Field Laboratory, enabling interdisciplinary research.

• Nanophotonics
• Infrared Spectroscopy
• Metamaterials
• +4 more

Prof. Dr. Thomas Taubner serves as a Professor at the Institute of Physics within the Faculty of Mathematics, Computer Science and Natural Sciences at RWTH Aachen University. He leads the IR Nano-Optics and Metamaterials research group, operating from Campus Melaten (Physics Building 26, Room A 104). His team focuses on cutting-edge nanophotonic technologies with applications in infrared optics and reconfigurable optical systems. Taubner's research spans nanophotonics, infrared spectroscopy, metamaterials, and phase-change materials, with particular expertise in plasmonic phase-change materials like In 3 SbTe 2 . His group pioneers techniques for dynamic control of light at the nanoscale through near-field microscopy, beam steering, and thermal emission manipulation. Key areas include 2D material characterization, phonon polariton engineering, and ultrafast optical phenomena in semiconductor heterostructures. Analysis of his recent publications reveals a dominant focus on programmable infrared nanophotonics using plasmonic phase-change materials. His work consistently demonstrates reconfigurable optical devices through direct laser writing, geometric phase metasurfaces, and real-space imaging of confined electromagnetic waves. The research shows strong interdisciplinary connections between condensed matter physics, materials science, and optical engineering, with practical applications in thermal management, sensing, and next-generation optical computing. Prof. Taubner actively supervises doctoral and master's students, regularly advertising thesis positions and doctoral openings through his research group. His team maintains advanced laboratory facilities for nanofabrication, near-field optical characterization, and ultrafast spectroscopy, supporting both fundamental research and technology development in infrared nanooptics.

• Semiconductor Materials
• Nanotechnology
• Condensed Matter Physics
• +3 more

Dr. Emmanouil Dimakis is a Researcher and Group Leader in the Spectroscopy department at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). His research focuses on semiconductor nanowires, plasmonics, and optoelectronics, with emphasis on strain engineering, heterostructure design, and advanced spectroscopic techniques such as THz and infrared nanospectroscopy. His work explores electronic and optical properties of nanomaterials, including III-V semiconductor systems, InGaN/GaN quantum wells, and core-shell nanostructures. Key themes include understanding strain effects on material performance, developing high-electron-mobility nanostructures, and optimizing optoelectronic devices for near-infrared applications. Dimakis' publications highlight innovations in nanowire growth methodologies, nonlinear plasmonic responses, and time-resolved analysis of carrier dynamics under extreme conditions. His group employs cutting-edge techniques like probe-corrected HRSTEM and THz pump-probe spectroscopy to uncover fundamental material behaviors. Despite no listed awards or grants in the provided text, his contributions to nanomaterials research and spectroscopic characterization are evident through his prolific publication record spanning over two decades. His research group at HZDR continues to advance the frontiers of semiconductor physics and nanotechnology.

Carolin MüllerView profile

Assistant Professor

• Computational Chemistry
• Molecular Dynamics
• Machine Learning
• +7 more

Carolin Müller is a Juniorprofessor for the Theory of Electronically Excited States at the Friedrich-Alexander University Erlangen-Nuremberg since November 2023. Previously, she was a Feodor Lynen Postdoctoral Researcher at the University of Luxembourg (June 2022-October 2023) and a Postdoctoral Researcher at Friedrich Schiller University Jena (March 2021-May 2022). Dr. Müller received her B.Sc. (2016) and M.Sc. (2018) in Chemistry from Friedrich Schiller University Jena, followed by her Ph.D. (Dr. rer. nat) in 2021 from the same institution. Her doctoral research focused on "Towards Operando Spectroscopy of Supramolecular Photocatalysts – A Case Study on Ru-dppz-derived Systems" under the supervision of Prof. B. Dietzek-Ivanšić. Dr. Müller's research focuses on the theoretical understanding of photoinduced processes in molecules and materials. Her group (CPC Group) investigates electron transfer processes, isomerization reactions, and excited-state dynamics with the goal of controlling and optimizing light-driven processes for increased reactivity and efficiency. Her work combines computational chemistry, spectroscopy, and machine learning approaches, specifically utilizing methods like TD-DFT, CASSCF, molecular/quantum dynamics, and cheminformatics techniques including SVD, MCR, and global/target lifetime analysis. Her recent publications demonstrate a strong interdisciplinary approach spanning computational chemistry, spectroscopy, and machine learning. Key themes include nonadiabatic molecular dynamics, excited-state simulations, photoswitch design, photocatalysis, and the development of computational tools like KiMoPack for kinetic modeling. Her work often bridges theoretical predictions with experimental validation through close collaboration with spectroscopy research groups. Feodor Lynen Research Fellowship (Alexander von Humboldt Foundation) Thuringian Research Award 2023 for Applied Research Albert-Weller Award (German Chemical Society) Dissertation Award (Faculty of Chemistry and Earth Sciences) FCI Kekulé PhD fellowship As a Juniorprofessor, Dr. Müller leads the CPC Group at FAU, where she mentors students in computational chemistry research. She has developed expertise in combining spectroscopic techniques (resonance Raman, transient absorption, and time-resolved emission spectroscopy) with computational methods and cheminformatics approaches. She also actively contributes to the scientific community through service roles including co-organizing the ESTML 2023 Workshop and serving as an active member in the yPC organization of the German Bunsen Society. Dr. Müller is actively developing the CPC Group research program at the Computer Chemistry Center, focusing on light-induced physical processes and chemical reactions. Her group combines quantum chemistry, chemoinformatics, and experimental spectroscopy to reveal mechanisms behind photoinduced phenomena and optimize light-driven processes.

Maurits HaverkortView profile

Professor

• Strongly Correlated Electron Systems
• Quantum Many-Body Physics
• X-ray Spectroscopy
• +6 more

Maurits Haverkort is a Professor at the Institute for Theoretical Physics, Heidelberg University (Germany). His research focuses on quantum many-body systems , strongly correlated electrons , and X-ray spectroscopy of complex materials under strong fields. University of Cologne (PhD in Physics, 2005) University of Groningen (M.Sc. in Physics, 2002) Research Interests : He investigates orbital and magnetic properties in heavy fermion systems , actinide materials , and correlated oxides using resonant inelastic X-ray scattering (RIXS) , ARPES , and computational tools like Quanty . His work spans crystal field theory , spin-orbit coupling , and ultrafast electron dynamics . Scientific Awards & Activities : 2018 – Editorial Board Member, Physical Review Letters 2017 – Beam Time Allocation Panel, ESRF Grenoble 2016–2018 – Swedish Research Council Panel NT-4 2012–2016 – Scientific Selection Panel, Helmholtz-Zentrum Berlin Recent Publications highlight 5f electron counting , photon-modulated bonding , and precision neutrino mass experiments , reflecting his expertise in quantum materials and advanced spectroscopy .

Thomas FennelView profile

Professor

• Strong-Field Physics
• Ultrafast Processes
• Nanoplasma Dynamics
• +3 more

Prof. Thomas Fennel is a faculty member at the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, leading the department A1: Strong Field Processes at Extreme Wavelengths. His research focuses on ultrafast phenomena in strong-field physics, nanoplasma dynamics, and quantum coherent imaging. He has pioneered work on attosecond electron emission, laser-driven nanoplasma expansion, and light-induced dynamics in nanoscale systems. His educational background includes advanced studies in physics and optics, though specific degrees are not detailed here. His lab specializes in experimental and theoretical investigations of extreme light-matter interactions, particularly at the nanoscale. Key techniques include time-resolved spectroscopy, diffraction imaging, and ultrafast laser systems. Recent publications explore topics like subcycle metallization of nanoparticles, attosecond electron emission from metal tips, and quantum coherence in nanostructures. These contributions highlight his leadership in advancing ultrafast science and nanoscale optics. No awards are explicitly mentioned, though his prolific publication record indicates significant contributions to the field. He collaborates extensively with international teams on projects involving femtosecond imaging, plasma dynamics, and strong-field ionization. His work bridges fundamental physics with applications in nanotechnology and quantum photonics, positioning him as a key figure in modern ultrafast science.

Joshua BarhamView profile

Assistant Professor

• Synthetic Photoelectrochemistry
• Photoredox Catalysis
• Flow Chemistry
• +4 more

Dr. Joshua Barham is a Sofja Kovalevskaja Group Leader at the University of Regensburg, Faculty of Chemistry and Pharmacy, Institute of Organic Chemistry. He leads an active research group known as 'The Bear Clan' focusing on cutting-edge synthetic methodologies that bridge photochemistry and electrochemistry. His research program has established him as a leading figure in the emerging field of synthetic photoelectrochemistry. Barham's research interests center on developing innovative synthetic methodologies at the intersection of photochemistry and electrochemistry. His lab explores how light energy and electrical energy can be synergistically combined to overcome fundamental limitations of traditional photoredox catalysis and synthetic organic electrochemistry. His team has pioneered concepts like electrochemically-mediated PhotoRedox Catalysis (e-PRC) and interfacial PhotoElectroChemistry (dPEC), which enable the activation of strong chemical bonds under mild conditions while improving atom economy. His publication record demonstrates a clear trend toward increasingly sophisticated integration of photochemical and electrochemical techniques in organic synthesis. The research spans from fundamental mechanistic studies to practical applications in sustainable chemistry, with particular emphasis on C-H functionalization, bond activation, and the development of novel reaction platforms. His work frequently appears in high-impact journals with numerous cover features and highly cited papers. Sofja Kovalevskaja Award Reaxys Ph.D. Prize Barham actively mentors a diverse team of researchers including multiple PhD students, postdoctoral fellows, and visiting scholars. His group has secured funding through prestigious programs including the Sofja Kovalevskaja Award, Elitenetzwerk Bayern, and DFG SPP2370 grants. The research has resulted in numerous high-impact publications, patents, and press coverage highlighting the innovative nature of the work. The Barham Lab operates state-of-the-art facilities for photoelectrochemical research, flow chemistry, and microwave synthesis. The group has developed specialized equipment including continuous flow photoreactors and microwave flow systems that enable safer, more efficient chemical transformations. Their 'Electrifying Photochemistry' research program continues to push boundaries in sustainable synthetic methodology development.

Manish GargView profile

Researcher

• Attosecond Science
• Quantum Microscopy
• Ultrafast Spectroscopy
• +7 more

Dr. Manish Garg is the Head of the Research Group 'Quantum Microscopy and Dynamics' at the Max Planck Institute for Solid State Research in Stuttgart, Germany. He holds a Group Leader (W2) position since 2024, having previously served as a Research Group Leader from 2020-2023 in the Department of Nanoscale Science. His research integrates attosecond science, scanning tunneling microscopy, and ultrafast Raman spectroscopy to develop a four-dimensional quantum microscope capable of capturing electrons and atoms in action at fundamental space-time limits. PhD (Dr. rer. nat.) in Physics from LMU Munich, Germany (2012-2017) Integrated B.S.-M.S. from Indian Institute of Science Education and Research, Kolkata, India (2007-2012) Dr. Garg's research focuses on developing techniques to observe and control quantum phenomena at the atomic scale. His group has pioneered methods to visualize electron dynamics with attosecond temporal resolution and sub-Ångström spatial resolution, enabling unprecedented insights into molecular processes. Recent breakthroughs include selective excitation of molecular vibrations, real-time tracking of electron oscillations in nanodevices, and imaging coherent phonon wave packets in graphene nanoribbons. His publication record shows a consistent trajectory of high-impact research in leading journals including Nature, Science, and Nature Communications. The work demonstrates expertise across multiple disciplines including attosecond physics, nanoscale imaging, quantum dynamics, and ultrafast spectroscopy, with applications ranging from fundamental quantum mechanics to potential light-wave electronics. Rudolf-Kaiser Preis (2023) Max-Auwärter Award (2022) IMPRS Advanced Photon Science Graduate Fellowship (2012-2016) INSPIRE Fellowship, DST India (2007-2012) Dr. Garg leads a research group comprising postdocs and PhD students working on cutting-edge quantum microscopy techniques. His group has secured significant recognition for developing methods to directly measure electron oscillations in quantum nanodevices and visualize atomic motion in single molecules. Current research focuses on advancing four-dimensional quantum microscopy to capture electronic and atomic dynamics in molecules, two-dimensional materials, and superconductors at fundamental space-time limits. The Quantum Microscopy and Dynamics group operates within specialized facilities at the Max Planck Institute for Solid State Research, utilizing low-temperature scanning tunneling microscopes operating in ultrahigh-vacuum conditions. Their work on picocavities and nonlinear optical spectroscopy at atomic length scales represents the frontier of quantum measurement science.

Olga SmirnovaView profile

Professor

• Nonlinear Optics
• Attosecond Science
• Strong-Field Physics
• +4 more

Prof. Olga Smirnova is a leading researcher at the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, heading the Strongfield Theory Group. Her work focuses on ultrafast phenomena, attosecond science, and quantum control in strong laser fields. She specializes in chiral dynamics, valleytronics, and high-harmonic generation, with contributions to understanding spin polarization and enantiosensitivity in molecular systems. Research interests include manipulating light-matter interactions at attosecond timescales, exploring topological photonics, and developing novel spectroscopic techniques like TACOS (Terahertz-Assisted Chiro-Optical Spectroscopy). Her theoretical advancements bridge fundamental physics and applications in chiral discrimination, ultrafast imaging, and valleytronics in 2D materials. Recent studies highlight discoveries such as multi-THz quantum beats in superfluorescent emission and polarization-shaped control of valley polarization in MoS 2 . Her work frequently interfaces with experimental groups, driving advancements in free-electron laser technologies and attosecond interferometry. Awards: Ahmed Zewail Award in Ultrafast Science and Technology (2020) Collaborations: Extensive international partnerships with institutions like DESY, Lund University, and the University of Rostock. Labs/Groups: Strongfield Theory Group at MBI, focusing on theoretical and computational modeling of ultrafast processes in intense laser fields.