Attosecond X-ray Spectroscopy of Ultrafast Dynamics in the Condensed Phase

Lead Research Organisation: Imperial College London
Department Name: Physics


We are all familiar with the idea that X-rays can "see" inside matter, after all this is the basis of much imaging technology from medical X-rays to Superman's astounding vision. We plan to use new sources of X-rays with the unique property that they are in pulses of duration less than 1 femtosecond (1 fs= 10^-15 s that is a millionth of a billionth of a second) to allow us, for the first time, to take snapshots and even make movies of some of the fastest events that occur within matter.
Our ability to produce and use such short pulses of X-rays has come out of our research over the past six years (funded by an ERC Advanced Grant and an EPSRC Programme Grant). We showed that high harmonic generation (HHG) based sources of ~0.3 fs pulse duration could be generated from 150 - 600 eV, an unprecedented achievement for ultrafast X-ray sources. Combined with the ultra-thin liquid sheet jets that we have recently invented and few-femtosecond optical pulses available in our laboratory that can start the clock by electronic excitation of the material, we have now in place the tools that enable a new kind of ultrafast X-ray spectroscopy that can be applied to any system whether it is in gas, liquid or solid state. We now want to advance this research in new directions by using this method to investigate some of the fastest processes in physics and chemistry.
In parallel with our laser research we have been working with international teams to develop the methods of using X-ray free electron laser facilities to make measurements on the few-femtosecond timescale. This has included work with LCLS (SLAC, California) in a two-pulse/two-colour mode with ~ 3 fs temporal resolution. Later this year it is anticipated that LCLS will produce the first FEL based sub-femtosecond X-ray pulses of extreme brightness (> 10^6 times greater than our HHG source). We plan to use this new capability to develop a new concept in X-ray non-linear spectroscopy that will allow us to precisely follow electron motions in matter at atomic spatial resolution and with time-scales faster than a femtosecond.
What will we investigate with these remarkable new tools? The answer is the fundamental dynamical events in physics, such as exciton formation and charge migration, and key processes in chemistry, such as electron transfer and bond-breaking/making. These can occur within 10 fs of initial electronic excitation and have hitherto not been accessible to direct measurement. Moreover with our tools we can track the dynamics of microscopic systems across the boundary in the temporal domain between quantum and classical behaviour. In condensed phase systems, where the quantum coherence of the initial state is lost in a few 10's of femtoseconds, this will allow us to see into a new quantum regime of dynamics. In particular we will focus on structures containing delocalised electrons (pi-conjugated systems) as in this case the electrons are highly mobile and so can display the very fastest dynamics. Additionally pi-conjugated molecules are the building blocks of polymers and molecular complexes of great interest in photochemistry and solar-energy conversion. Not only will our measurements capture the ultrafast electronic motion in these systems they will also allow us to measure the structural dynamics associated with isomerization, ring opening and other chemical changes.
Our research will extend the frontier of science's measurement capability in the time domain with the likelihood of measuring physical processes at timescales 100 times faster than before. This will lead to new breakthroughs in our understanding of quantum dynamical processes in nature and technology.

Planned Impact

As well as academic beneficiaries the research outcomes in photocatalysis and optoelectronics have a high potential to impact the Catalysis and Renewable Energy industrial sectors. In parallel there is a resulting societal benefit in terms of efficient use of resources for chemical synthesis and renewable energy production. To capture this we will continue to work with industrial contacts (e.g. in Johnson-Mathey, GSK and Rolls-Royce) and will organise a follow up meeting to the very successful one on "Applications of Ultrafast X-rays" that was hosted at Imperial College in 2016.
An important impact to the national science and technology workforce will be in providing a number of highly skilled researchers trained in the methods of ultrafast X-ray measurement. This will address a developing skills gap in the UK as we don't yet host, or plan to host, an X-ray FEL facility of our own, but we do plan to make use of the internationally available facilities for both scientific and technological research in the future (see report issued by STFC on X-ray FELs in 2016).
The research will result in the development of technology that may be widely used by the technology community in the private sector and public research arena as well as having potential for commercial development. The technology that may be most relevant are compact soft X-ray ultrafast coherent light sources, few-cycle high power laser pulses tuneable in the IR and new liquid jet technology. First the sub-fs soft X-ray pulses we can generate from table top (and hence portable) apparatus represents a new technological capability. They can be applied to X-ray spectroscopic analysis of a wide range of materials and can capture transients at all timescales. This may prove critical for future methods of in-situ measurements on chemical reactors, combustion and other industrial processes. Second the few cycle waveform controlled mid-IR pulses, again generated from a relatively compact apparatus, may find application in remote sensing (e.g. for environmental monitoring) and defence/security (stand-off detection of chemicals). Important wavelength bands we plan to open up by this research include the 1100-1600 nm, and in the UV, and along with the mid-IR these may find application in spectroscopic analysis and environmental monitoring. Aspects of the work already completed on few cycle sources are now being developed towards commercialisation via funding from an ERC Proof-of-Concept grant. Third the new liquid sheet jet technology is already exciting the interest of an industrial partner ("Rho nano" UAB, Lithuania) and through the new project we hope to greatly extend the capability of this technology to handle a large range of liquids and to handle smaller volumes of high value sample. This may have impact in the Chemical Analysis, Biomedical and Pharmaceuticals sectors.


10 25 50
Description First measurement of signatures of excitons dynamics in organic semiconductors using high harmonic based time-resolved X-ray spectroscopy. The analysis of this data shows evidence for initial ultrafast delocalisation of the hot excitons across neighbouring polymer units on a few femtosecond timescale followed by cooling and localisation over tens of femtoseconds. This demonstrates the power of the method. Manuscript on arxiv.

HHG characterised from liquid targets, and the mechanism of electron recollision persisting in, but partially frustrated by collisions, has emerged from our analysis of this data. Manuscript in preparation.

X-ray attosecond pulses demonstrating non-linear impulsive electronic Raman (published PRL 2020), few femtosecond resolved transient electronic hole states (PRX 2021) and core excited electronic wavepackets (Science 2022)

First experiments of X-ray absorption in liquids have been accomplished with work ongoing to improve S/N and eliminate problems from contamination of the X-ray optics by the solute.

First demonstration of Attosecond one and two colour pulses from an X-ray laser. Published Nature Photonics Jan 2020

First demonstration of impulsive X-ray electronic Raman in a small molecule. Published PRL August 2020.
Exploitation Route Being developed under this grant. Hoping to roll out some of this capbility to Artemis, ELI-ALP.

This work has informed the Science Case for a UK XFEL and in the fullness of time may impact a UK XFEL and other XFELs
Sectors Aerospace

Defence and Marine




Pharmaceuticals and Medical Biotechnology

Description The confirmation of attosecond pulses from XLEAP at LCLS (SLAC, Stanford) has influenced the outline design of a potential UK XFEL as presented in the UK XFEL Science Case (Published UKRI October 2020). Moreover, the demonstration of the application to non-linear X-ray science and attosecond science has opened new technical capabilities with applications across science and technology.T Over the period 2021-2022 we conducted several beamtimes both remotely and in person that have demonstrated new principles of attosecond measurement and attosecond x-ray non-linear optics. This has influenced the development of the UK XFEL project which is now active, and led to the recent award of new funding. We also conducted the first studies of exciton delocalisation/localisation dynamics in organic semiconductors with photovoltaic applications.
First Year Of Impact 2020
Sector Chemicals,Energy
Impact Types Policy & public services

Description Science Lead UK XFEL Project 2019-2025
Geographic Reach National 
Policy Influence Type Contribution to a national consultation/review
Description Attosecond Electronic Dynamics of the Valence States in Matter Measured with XFELs
Amount £834,035 (GBP)
Funding ID EP/X026094/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 04/2023 
End 04/2026
Description Ultrafast Photochemical Dynamics in Complex Environments
Amount £8,055,186 (GBP)
Funding ID EP/V026690/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 08/2021 
End 08/2027
Title Proving of utility of attosecond X-ray pulses from XFELs 
Description We have used the XLEAP (attosecond pulse mode) in both single colour and two-colour format to demonstrate new capability in X-ray non-linear optics, X-ray pump-probe spectroscopy and time resolving photoelectron emission. 
Type Of Material Improvements to research infrastructure 
Year Produced 2020 
Provided To Others? Yes  
Impact So far a number of high profile publications in PRX, PRL and Science 
Description Bucksbaum Group - Stanford University 
Organisation Stanford University
Country United States 
Sector Academic/University 
PI Contribution We have provided ideas and expertise to progress research in ultrafast X-ray science by leading and participating in a number of joint beamtimes.
Collaborator Contribution Through this collaboration we have been able to efficiently engage in X-ray free electron laser research at the LCLS facility SLAC through their local resources and manpower. It has enabled around 10 separate beam-times.
Impact A number of research papers including 1 PRL, 2 Nature Communications and more in preparation.
Start Year 2011
Description SLAC Photon Sciences 
Organisation Stanford University
Department SLAC National Accelerator Laboratory
Country United States 
Sector Public 
PI Contribution We are a member of an international collaboration, the "Attosecond Campaign" coordinated by SLAC (Dr Agostino Marinelli and Dr James Cryan SLAC leads) aimed at developing attosecond measurements of electron dynamics using newly proven X-ray FEL capabilities.
Collaborator Contribution They provide the support of X-ray FEL beamtime and run the experimental endstation
Impact A papers published in PRL, Nature Photonics, Science
Start Year 2020