The inherent delay between the emission of the two kinds of electron results in a particular ellipse in the analyzed information. In principle, the position of individual information points around the ellipse can be checked out like the hands of a clock to reveal the precise timing of the dynamical processes. Credit: Daniel Haynes/J örg Harms
New technique delivers resolution improvement in ultrafast processes.
An international consortium of researchers, started by Reinhard Kienberger, Professor of Laser and X-ray Physics at the Technical University of Munich (TUM), numerous years back, has made substantial measurements in the femtosecond variety at the U.S. Stanford Linear Accelerator Center (SLAC).
However, on these minuscule timescales, it is extremely hard to integrate the X-ray pulse that stimulates a reaction in the sample on the one hand and the laser pulse which observes it on the other. This issue is called timing jitter, and it is a significant obstacle in ongoing efforts to carry out time-resolved experiments at XFELs with ever-shorter resolution.
The inherent delay in between the emission of the two types of electron leads to a characteristic ellipse in the analyzed data. The X-ray pulse ejects photoelectrons from the sample, leading to their replacement by electrons in outer shells. As these outer electrons relax, they release energy which can later cause the emission of another electron, understood as an Auger electron.
Radiation damage is triggered by both the intense X-rays and the continued emission of Auger electrons, which can rapidly deteriorate the sample.” Crucially, in each measurement, the Auger electrons always interact with the spotting laser pulse slightly later on than the photoelectrons displaced at first, since they are emitted later,” states Prof. Reinhard Kienberger, who helped to develop the experiments style.
Now, a large worldwide research group has actually established an approach to get around this problem at XFELs and demonstrated its effectiveness by measuring a basic decay process in neon gas.
Good timing can prevent radiation damage
The X-ray pulse ejects photoelectrons from the sample, leading to their replacement by electrons in external shells. As these external electrons unwind, they release energy which can later cause the emission of another electron, known as an Auger electron.
Radiation damage is triggered by both the extreme X-rays and the continued emission of Auger electrons, which can rapidly break down the sample. Timing this decay would help to avert radiation damage in experiments studying various molecules. In addition, Auger decay is an essential criterion in research studies of unique, highly thrilled states of matter, which can only be investigated at XFELs.
Research team provides pioneering and extremely accurate approach
To chart Auger decay the scientists used a strategy dubbed self-referenced attosecond spotting, which is based upon mapping the electrons in thousands of images and deducing when they were emitted based on international patterns in the information.
For the first application of their method, the group utilized neon gas, where the decay timings have been presumed in the past. After exposing both photoelectrons and Auger electrons to an external streaking laser pulse, the scientists identified their final kinetic energy in each of tens of countless individual measurements.
” Crucially, in each measurement, the Auger electrons constantly interact with the spotting laser pulse a little later than the photoelectrons displaced initially, because they are produced later on,” says Prof. Reinhard Kienberger, who helped to develop the experiments style. “This continuous factor forms the foundation of the strategy.” By integrating numerous specific observations, the team was able to construct an in-depth map of the physical procedure, and thereby figure out the particular dead time in between the picture- and Auger emission.
Spotting method causes success
In several initial documents of our group, we have carried out time-resolved measurements on free-electron lasers using the streaking approach,” says TUM PhD student Albert Schletter, co-author of the publication. “Using this technique, we were able to measure the hold-up in between X-ray ionization and Auger emission in neon gases with the highest accuracy,” explains lead author Dan Haynes of Hamburgs Max Planck Institute for the Structure and Dynamics of Matter.
The researchers are hopeful that self-referenced spotting will have a broader effect in the field of ultrafast science. “Self-referenced streaking might facilitate a new class of experiments taking advantage of the flexibility and extreme strength of XFELs without jeopardizing on time resolution,” adds co-author Markus Wurzer, who is a PhD trainee of Prof. Kienberger.
For more on this research, see Clocking the Movement of Electrons Inside an Atom– Down to a Millionth of a Billionth of a Second.
Recommendation: “Clocking Auger electrons” by D. C. Haynes, M. Wurzer, A. Schletter, A. Al-Haddad, C. Blaga, C. Bostedt, J. Bozek, H. Bromberger, M. Bucher, A. Camper, S. Carron, R. Coffee, J. T. Costello, L. F. DiMauro, Y. Ding, K. Ferguson, I. Grguraš, W. Helml, M. C. Hoffmann, M. Ilchen, S. Jalas, N. M. Kabachnik, A. K. Kazansky, R. Kienberger, A. R. Maier, T. Maxwell, T. Mazza, M. Meyer, H. Park, J. Robinson, C. Roedig, H. Schlarb, R. Singla, F. Tellkamp, P. A. Walker, K. Zhang, G. Doumy, C. Behrens and A. L. Cavalieri, 18 January 2021, Nature Physics.DOI: 10.1038/ s41567-020-01111-0.
