Pulse envelope effect on nonlinear Compton scattering in electron-laser collisions

Abstract

Nonlinear Compton scattering is calculated for the collision of an electron with a plane wave pulse. A mid infra-red (IR) peak arises in the photon spectrum due to long-range interference associated with the pulse envelope. The case of a flat-top pulse is studied as a toy model for pulse envelope effects and reduced to two final-state momentum integrations; the case of a sine-squared pulse is studied numerically. A perturbative expansion in charge-field coupling reveals that already at intermediate intensities, many orders are required to correctly capture the structure of the mid-IR peak. By regularising the classical result, it is shown that the mid-IR peak is due to plane-wave ponderomotive effects on the pulse envelope. Finally, it is shown that the mid-IR peak can be isolated using energy, angle and polarisation filters.

Generation of quasi-monoenergetic positron beams in chirped laser fields

“…Employing a many-cycle laser pulse will lead to outgoing photon spectra similar to those in a monochromatic background [3,4]: well-defined harmonic fringes in lightfront momenta and emission angle. Collision with short laser pulses will lead to a broadening of outgoing particle harmonic peaks [5][6][7] and richer spectral structures: infrared structure [8,9], asymmetry in emission angle [10], and pronounced interference phenomena [11,12]. The spectral broadening can be attributed to the inhomogeneous effective mass of the charged particle moving in the intense laser pulse [13][14][15][16]: the variation of the effective mass modifies the velocity of the changed particle during the scattering [17][18][19][20].…”