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#### Numerical approach to the semiclassical method of radiation emission for arbitrary electron spin and photon polarization

##### External Resource

https://journals.aps.org/prd/pdf/10.1103/PhysRevD.100.116001

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##### Fulltext (public)

1909.12899.pdf

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##### Citation

Wistisen, T. N., & Di Piazza, A. (2019). Numerical approach to the semiclassical
method of radiation emission for arbitrary electron spin and photon polarization.* Physical Review
D,* *100*(11): 116001. doi:10.1103/PhysRevD.100.116001.

Cite as: https://hdl.handle.net/21.11116/0000-0005-54EF-0

##### Abstract

We show how the semiclassical formulas for radiation emission of Baier,

Katkov and Strakhovenko for arbitrary initial and final spins of the electron

and arbitrary polarization of the emitted photon can be rewritten in a form

which numerically converges quickly. We directly compare the method in the case

of a background plane wave with the result obtained by using the Volkov state

solution of the Dirac equation, and confirm that we obtain the same result. We

then investigate the interaction of a circularly polarized short laser pulse

scattering with GeV electrons and see that the finite duration of the pulse

leads to a lower transfer of circular polarization than that predicted by the

known formulas in the monochromatic case. We also see how the transfer of

circular polarization from the laser beam to the gamma ray beam is gradually

deteriorated as the laser intensity increases, entering the nonlinear regime.

However, this is shown to be recovered if the scattered photon beam is

collimated to only allow for passage of photons emitted with angles smaller

than $1/\gamma$ with respect to the initial electron direction, where $\gamma$

is the approximately constant Lorentz factor of the electron. The obtained

formulas also allow us to answer questions regarding radiative polarization of

the emitting particles. In this respect we briefly discuss an application of

the present approach to the case of a bent crystal and high-energy positrons.

Katkov and Strakhovenko for arbitrary initial and final spins of the electron

and arbitrary polarization of the emitted photon can be rewritten in a form

which numerically converges quickly. We directly compare the method in the case

of a background plane wave with the result obtained by using the Volkov state

solution of the Dirac equation, and confirm that we obtain the same result. We

then investigate the interaction of a circularly polarized short laser pulse

scattering with GeV electrons and see that the finite duration of the pulse

leads to a lower transfer of circular polarization than that predicted by the

known formulas in the monochromatic case. We also see how the transfer of

circular polarization from the laser beam to the gamma ray beam is gradually

deteriorated as the laser intensity increases, entering the nonlinear regime.

However, this is shown to be recovered if the scattered photon beam is

collimated to only allow for passage of photons emitted with angles smaller

than $1/\gamma$ with respect to the initial electron direction, where $\gamma$

is the approximately constant Lorentz factor of the electron. The obtained

formulas also allow us to answer questions regarding radiative polarization of

the emitting particles. In this respect we briefly discuss an application of

the present approach to the case of a bent crystal and high-energy positrons.