Attosecond XFEL and Beyond

Jiawei Yan

Ultra-high-power hard X-ray attosecond pulse generation and applications

My current main focus is the generation and application of ultra-high-power hard X-ray attosecond pulses. More broadly, I work on advanced X-ray free-electron laser science, especially when source physics can be pushed toward stronger temporal compression, higher peak power, richer pulse structure, and more useful experimental capability.

My research spans attosecond XFELs, spatiotemporal shaping of X-ray pulses, fully coherent high-repetition-rate FELs, and AI for Science. At the center is a broader question: how can we move toward complete control over X-ray pulses?

Attosecond XFEL X-ray pulse shaping Fully coherent high-repetition-rate FEL AI for Science

About

Centered on hard X-ray attosecond pulse generation, then extended outward

The center of gravity of my current work is ultra-high-power hard X-ray attosecond pulse generation and its application to new ultrafast X-ray science.

I am based in Hamburg and work on advanced XFEL science across theory, numerical design, and experimental implementation. My current research program focuses on advancing hard X-ray attosecond pulse generation toward higher peak power, stronger controllability, and broader experimental impact, especially where pulse properties can be deliberately matched to demanding ultrafast measurements.

Around this main line, I work on several connected problems: shaping X-ray pulses in both time and space, developing routes toward fully coherent high-repetition-rate FEL operation, and using AI and optimization methods to make accelerator and light-source physics more efficient and more programmable.

I do not see these as separate topics. They are parts of one broader objective: complete control over X-ray pulses, from pulse duration and wavefront structure to coherence, stability, diagnostics, and machine intelligence.

JY

Current emphasis

  • Ultra-high-power hard X-ray attosecond pulse generation and applications
  • Spatiotemporal shaping of structured X-ray pulses
  • Fully coherent high-repetition-rate FEL concepts and seeded FEL physics
  • Bayesian and AI-assisted optimization for accelerator-based light sources

Research

Four research themes

Attosecond XFELs, X-ray pulse shaping, coherent high-repetition-rate FELs, and AI for Science.

01

Attosecond XFEL

Hard X-ray attosecond pulses are a uniquely powerful route to resolving electronic motion and nonequilibrium dynamics on their natural timescales. The challenge is not merely to reach the attosecond regime, but to do so with sufficiently high peak power and with pulse properties that are actually useful for experiments.

This is my primary focus. I work on the generation and application of ultra-high-power hard X-ray attosecond pulses, with emphasis on beam shaping, pulse compression, source optimization, diagnostics, and the transition from proof-of-principle generation to robust scientific use.

02

Spatiotemporal shaping of X-ray pulses

Once pulse duration becomes controllable, the next question is whether one can also shape waveform, phase, and transverse mode content at the source. This matters because many future X-ray experiments will need not just shorter pulses, but pulses with designed spatiotemporal structure.

I study methods for directly shaping X-ray pulses in time and space, including orbital-angular-momentum control and other routes to wavefront-engineered or waveform-engineered X-ray emission.

03

Fully coherent high-repetition-rate FEL

Fully coherent FEL operation at high repetition rate is a major goal for next-generation light sources, but standard seeded FEL schemes run into practical limits, especially in seed-laser power and scalability. More generally, the question is how to retain seeded-FEL coherence while removing those bottlenecks.

In my work, the most concrete example is the self-modulation seeded FEL mechanism, which I proposed and experimentally validated. More broadly, I am interested in how self-modulation HGHG and related mechanisms can support compact, high-average-power EUV FELs as well as more general coherent high-repetition-rate FEL development.

04

AI for Science

Accelerator and FEL systems are already too high-dimensional and too nonlinear to rely only on manual tuning or brute-force scans. If we want light sources to become more adaptive and more precisely controlled, intelligent optimization must become part of the physics workflow.

I use Bayesian optimization, machine learning, and physics-informed algorithms for machine studies, FEL design, and operational optimization, especially where these methods can improve both physical insight and practical controllability.

Papers

Selected papers

Recent work.

  1. Terawatt-attosecond hard X-ray free-electron laser at high repetition rate

    J. Yan et al. Nature Photonics 18, 1293–1298 (2024)

  2. AttoSHINE: Generation of continuous-wave terawatt-scale attosecond X-ray pulses at SHINE

    B. Yan, C. Xu, S. Chen, D. Gu, Y. Chen, J. Yan, H. Deng. Ultrafast Science (2026)

  3. Spatiotemporal shaping of attosecond X-rays with time-dependent orbital angular momentum

    C. Xu, J. Yan, G. Geloni, C. Lechner, H. Deng. arXiv:2508.19020v2

  4. Self-seeded free-electron lasers with orbital angular momentum

    J. Yan and G. Geloni. Advanced Photonics Nexus 2(3), 036001 (2023)

  5. Self-Amplification of Coherent Energy Modulation in Seeded Free-Electron Lasers

    J. Yan et al. Physical Review Letters 126, 084801 (2021)

  1. First observation of laser-beam interaction in a dipole magnet

    J. Yan et al. Advanced Photonics 3(4), 045003 (2021)

  2. Self-enhanced coherent harmonic amplification in seeded free-electron lasers

    H. Yang, J. Yan, H. Deng. Fundamental Research (2024)

  3. High-repetition-rate seeded free-electron laser enhanced by self-modulation

    H. Yang, J. Yan, H. Deng. Advanced Photonics Nexus 2(3), 036004 (2023)

  4. Cascaded hard X-ray self-seeded free-electron laser at megahertz repetition rate

    S. Liu et al. Nature Photonics 17, 984–991 (2023)

  5. Multi-Beam-Energy Control Unit Based on Triple-Bend Achromats

    L. Wu et al. Photonics 12(3), 275 (2025)

Highlights

Current directions and future plans

Attosecond pulse generation, coherent FEL concepts, diagnostics, and applications.

Toward complete control over X-ray pulses

The central aim is not only to make XFEL pulses shorter or more intense, but to make them deliberately shapeable. That means engineering the electron beam, the seeding process, and the FEL interaction so that the final X-ray pulse carries useful structure in duration, phase, topology, and coherence.

In this view, attosecond XFELs, structured X-ray pulses, coherent FEL control, and machine intelligence are not isolated projects. They all serve the same long-term goal: achieving as complete control over X-ray pulses as possible.

Shared scientific thread

  • Electron-beam phase-space control
  • Direct shaping of ultrafast X-ray waveforms
  • Coherence and scalability at high repetition rate
  • Data-driven operation of complex accelerator systems

Future directions

Looking ahead, I want to develop compact attosecond XFEL concepts, diagnostics tailored to attosecond XFEL pulses, and new applications that fully exploit the unique combination of hard X-ray photon energy, attosecond duration, and high peak power.

On the coherent FEL side, I am also interested in whether self-modulation HGHG and related mechanisms can support compact, high-average-power EUV FEL development.

Visuals

Research visuals

Selected cover and concept visuals related to recent work.

Attosecond XFEL visual
Nature Photonics 2024

Attosecond XFEL

Concept visual for ultra-high-power hard X-ray attosecond pulse generation.

Self-seeded OAM visual
APN 2023

Self-seeded OAM

Structured X-ray pulses with orbital angular momentum.

Self-modulation HGHG visual
PRL 2021 / APN 2023

Self-modulation HGHG

Visual work related to self-modulation seeded FEL and coherent harmonic control.

Laser-beam interaction visual
Advanced Photonics 2021

Laser-beam interaction

Concept visual for laser-beam interaction in a dipole magnet.

Contact

Contact and profiles

Academic correspondence and collaborations.

Email

Academic correspondence.

Location

Hamburg, Germany