Good evening! While my fan heater is doing its job, why don't we catch some electrons? 
In yesterday's thread, the electrons which have been freed from their bound state by the laser mostly just oscillated around (steered by the electric field) and eventually flew off and away (until they hit a detector).
https://twitter.com/RealSci_Nano/status/1326189495805505536?s=20
However, not all electrons are so lucky. For some of them, their trajectory ends up looking almost like that lasso up there. This is if their kinetic energy at the end of the laser pulse is not quite enough to escape from the Coulomb potential of the atom/ion.
The nucleus is marked by the "x" at position (0,0,0). The electron exits from the quantum tunnel (beginning of the red dotted path) and starts oscillating in the laser field until it ends up on an elliptical, bound trajectory (blue dotted) once the pulse has passed.
The blue bound trajectory looks like a Kepler orbit, because the maths is (almost) the same: Planets are kept on their elliptical orbits by gravity, while electrons are bound by the Coulomb attraction with the ion (except, one is a quantum particle and one clearly isn't 😉).
Therefore, the final fate of these types of electrons is a highly excited bound state aka Rydberg state. And if we look at the entire process as one, there is no actual ionisation happening, in the end, we are left with a neutral, but highly excited, atom again.
I should probably also mention the units on the plots: a.u. = atomic units. Our preferred units because all the important reference quantities of an electron are set to unity. 1 a.u. in length equals the Bohr radius, approximately ½ Å.
If the laser is polarised linearly (or only has low ellipticity), a significant part of all tunnelled electrons ends up in Rydberg states. We can then use them for different purposes in our investigations,
for example:
for example:
taking them as a reference point to study shifts in the photoelectron momentum distribution
journals.aps.org/prl/abstract/1…
(OA: arxiv.org/abs/1408.2336)
journals.aps.org/prl/abstract/1…
(OA: arxiv.org/abs/1408.2336)
or searching for (and finding) non-adiabatic effects, meaning that the dynamics of the process is relatively fast and the wavefunction reacts to the entire temporal history rather than only a given instantaneous situation
journals.aps.org/pra/abstract/1…
(OA: arxiv.org/abs/1805.02384)
journals.aps.org/pra/abstract/1…
(OA: arxiv.org/abs/1805.02384)
(thread by @coenneli)
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