Profile
My research interests lie in the development of instruments and methods to expand our view of matter.
I mainly work with sources based on ultrafast lasers to produce ultrashort pulses of X-rays and electrons, to probe samples that have a societal and/or biological relevance, using imaging techniques often based on coherent diffraction. Check out some of my research highlights below! |
I use my hands a lot when I speak...
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CEP effects in Laser Wakefield Acceleration
(I'm presenting this work at the Optica High-Brightness Conference in Budapest, March 23)
In Laser Wakefield Acceleration, we can accelerate electrons to relativistic energies over a distance that is thousands of times smaller than with conventional accelerators. We do this by shooting an extremely short, extremely intense laser pulse in a gas. The laser is so intense that all the gas is immediately ionized and transformed in a plasma. As the laser pulse propagates through the plasma, it pushes the electrons away, causing a wake in the electron density behind the laser pulse, much like the wake in the water behind a boat. Under the right circumstances, electrons can leave the plasma, start 'surfing' this wake, and be accelerated to almost the speed of light after just tens of micrometers.
This video is a simulation I performed of this process. What is special about this particular simulation, is that I use a laser pulse that is so incredibly short, that it consists of just a few cycles of the electric field of the laser light. When you use a pulse that short, the exact shape of the electric field becomes important. The intensity of the pulse is given by the so-called pulse envelope (the blue line). The electric field oscillates within this envelope (red line). As the pulse moves through the plasma (plasma density in shades of green), the phase of the electric field shifts with respect to the envelope (the so-called Carrier-Envelope Phase, or CEP). As it shifts, the plasma wake changes shape, wiggling up and down as the pulse propagates through the plasma.
The accelerated electron beam gets injected about 130 femtoseconds after the start of the simulation. Because the wake moves a bit sideways at the moment of injection, the electron beam gets injected a bit sideways as well, causing it to oscillate during acceleration, and leave the accelerator pointing a bit up or down.
We then tried to see this effect in our experiment. We use a laser pulse as short as 3.5 fs, of which we can precisely control the shape of the electric field (the carrier-envelope phase). The figures below summarize what we observed:
The angle with which the electron beam leaves the accelerator changes when we change the CEP of the laser pulse, exactly as predicted by the simulation. We are the first in the world to observe this effect!
This video is a simulation I performed of this process. What is special about this particular simulation, is that I use a laser pulse that is so incredibly short, that it consists of just a few cycles of the electric field of the laser light. When you use a pulse that short, the exact shape of the electric field becomes important. The intensity of the pulse is given by the so-called pulse envelope (the blue line). The electric field oscillates within this envelope (red line). As the pulse moves through the plasma (plasma density in shades of green), the phase of the electric field shifts with respect to the envelope (the so-called Carrier-Envelope Phase, or CEP). As it shifts, the plasma wake changes shape, wiggling up and down as the pulse propagates through the plasma.
The accelerated electron beam gets injected about 130 femtoseconds after the start of the simulation. Because the wake moves a bit sideways at the moment of injection, the electron beam gets injected a bit sideways as well, causing it to oscillate during acceleration, and leave the accelerator pointing a bit up or down.
We then tried to see this effect in our experiment. We use a laser pulse as short as 3.5 fs, of which we can precisely control the shape of the electric field (the carrier-envelope phase). The figures below summarize what we observed:
The angle with which the electron beam leaves the accelerator changes when we change the CEP of the laser pulse, exactly as predicted by the simulation. We are the first in the world to observe this effect!
First experimental observation of CEP-effects in Laser Wakefield Acceleration.
a): Principle of the experiment. b): The beam pointing as a function of the CEP, in the plane of the electric field (red line) and the perpendicular plane (blue line). c): Images of the electron beam on our detector for three different CEP values.
The simulation of the video above was published in Physics of Plasmas (as cover article!), while the experimental observation just got published in Physical Review X. The CNRS (French national research agency) published a popular science article about it (in French...)
a): Principle of the experiment. b): The beam pointing as a function of the CEP, in the plane of the electric field (red line) and the perpendicular plane (blue line). c): Images of the electron beam on our detector for three different CEP values.
The simulation of the video above was published in Physics of Plasmas (as cover article!), while the experimental observation just got published in Physical Review X. The CNRS (French national research agency) published a popular science article about it (in French...)
Broadband Coherent Diffractive Imaging
Coming soon: as part of my PhD research I developed a technique that allows to image samples in a way that was impossible before...
This work got published in Nature Photonics in 2020.
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