Thread by @RealSci_Nano

Hello everyone!
To talk about my research, I decided to theme it by "studying the ionisation process itself" (today) and "possible things that can happen afterwards" (tomorrow).

I'm going to keep the explanations in the threads fairly colloquial. But I will link the corresponding publications (open access whenever possible) so you can dig into the details there if you wish. Or of course, just ask me any questions you might have and I'll expand on that 😉

Yesterday I have already introduced the idea that the strong electric field of the laser pulse modifies the Coulomb potential which keeps electrons in bound states. The video shows a classical picture of this:

However, we are actually dealing with a quantum system, and for typical strong-field parameters, most of the ionisation processes happen by quantum-tunnelling through the potential barrier

One of the key questions which is still being investigated in detail is then, what the electron wavefunction looks like at the end of this tunnelling process. Does it have some momentum? How wide is its spread?

These characteristics are important because they determine where the electron (probability distribution) will go subsequently, and this is precisely what is measured at the end on a detector. (video not mine)

By comparing simulations with different momentum distributions along the tunnel-ionisation direction against a set of experimental measurements, we found that the (previously common) assumption of (almost) 0 momentum along that direction is not a good approximation.

publisher version:
doi.org/10.1088/0953-4…

open access (OA):
arxiv.org/abs/1303.3209

And this finding is independent of whether we are in an adiabatic regime (i.e. the wavefunction can always instantaneously adapt to any situation) or non-adiabatic (i.e. the temporal evolution matters)
doi.org/10.1103/PhysRe…
OA: researchgate.net/publication/27…

Another key question is: "how long does this process take?" ⏲️. At first glance, this might sound like a straightforward question, but since the phenomenon of quantum tunnelling has been discovered almost 100 years ago, there has been a debate about this.

So, #attoscience tries to time-resolve electron dynamics, where one of the dominant processes is quantum tunnelling 😉
Of course, our field developed both additional theories and several experiments to try and measure the/a tunnelling time

Most commonly, the laser field is elliptically polarised, so that the electric field rotates around like a clock, but still has clearly defined moments of strongest field leading to highest probability of ionisation

The interaction with the laser field after ionisation imprints the moment when an electron exits from the potential barrier onto the final momentum direction. This moment appears to be later than the maximum ionisation probability moment. (first image: doi.org/10.1038/s41586…)

Unfortunately, this "exit time↔️final momentum" mapping is disturbed by many factors, such as the Coulomb attraction of the parent ion, momenta/energy at the tunnel exit, and more. This debate still continues...
doi.org/10.1080/095003…

(thread by @coenneli)