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#### Investigation of two-photon emission in strong field QED using channeling in a crystal

##### External Resource

https://journals.aps.org/prd/pdf/10.1103/PhysRevD.100.036002

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##### Fulltext (public)

1905.05038.pdf

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##### Citation

Wistisen, T. N. (2019). Investigation of two-photon emission in strong field QED using
channeling in a crystal.* Physical Review D,* *100*(3):
036002. doi:10.1103/PhysRevD.100.036002.

Cite as: https://hdl.handle.net/21.11116/0000-0004-A90F-E

##### Abstract

We investigate the 2nd order process of two photons being emitted by a

high-energy electron dressed in the strong background electric field found

between the planes in a crystal. The strong crystalline field combined with

ultra relativistic electrons is one of very few cases where the Schwinger field

can be experimentally achieved in the electron's rest frame. The radiation

being emitted, the so-called channeling radiation, is a well studied

phenomenon. However only the first order diagram corresponding to emission of a

single photon has been studied so far. We elaborate on how the 2 photon

emission process should be understood in terms of a two-step versus a one-step

process, i.e., if one can consider one photon being emitted after the other, or

if there is also a contribution where the two photons are emitted

'simultaneously'. From the calculated full probability we see that the two-step

contribution is simply the product of probabilities for single photon emission

while the additional one-step terms are, mainly, interferences due to several

possible intermediate virtual states. These terms can contribute significantly

when the crystal is thin. Therefore, in addition, we see how one can, for a

thick crystal, calculate multiple photon emissions quickly by neglecting the

one-step terms, which represents a solution of the problem of quantum radiation

reaction in a crystal beyond the usually applied constant field approximation.

We explicitly calculate an example of 180 GeV electrons in a thin Silicon

crystal and argue why it is, for experimental reasons, more feasible to see the

one-step contribution in a crystal experiment than in a laser experiment.

high-energy electron dressed in the strong background electric field found

between the planes in a crystal. The strong crystalline field combined with

ultra relativistic electrons is one of very few cases where the Schwinger field

can be experimentally achieved in the electron's rest frame. The radiation

being emitted, the so-called channeling radiation, is a well studied

phenomenon. However only the first order diagram corresponding to emission of a

single photon has been studied so far. We elaborate on how the 2 photon

emission process should be understood in terms of a two-step versus a one-step

process, i.e., if one can consider one photon being emitted after the other, or

if there is also a contribution where the two photons are emitted

'simultaneously'. From the calculated full probability we see that the two-step

contribution is simply the product of probabilities for single photon emission

while the additional one-step terms are, mainly, interferences due to several

possible intermediate virtual states. These terms can contribute significantly

when the crystal is thin. Therefore, in addition, we see how one can, for a

thick crystal, calculate multiple photon emissions quickly by neglecting the

one-step terms, which represents a solution of the problem of quantum radiation

reaction in a crystal beyond the usually applied constant field approximation.

We explicitly calculate an example of 180 GeV electrons in a thin Silicon

crystal and argue why it is, for experimental reasons, more feasible to see the

one-step contribution in a crystal experiment than in a laser experiment.