Phase dependence of Thomson scattering in an ultraintense laser field

Abstract

The Thomson scattering spectra of an electron by an ultraintense laser field are computed. It is found that the electron orbit, and therefore its nonlinear Thomson scattering spectra, depend critically on the amplitude of the ultraintense laser field and on the phase at which the electron sees the laser electric field. Contrary to some customary notions, the Thomson scattering spectra, in general, do not occur at integer multiples of the laser frequency and the maximum frequency is proportional to the first instead of the third power of the electric field strength for the case of an ultraintense laser. The implications of these findings are discussed.

Thomson Scattering from Ultrashort and Ultraintense Laser Pulses

“…1 and t 0 ÿ4T ÿ80 fs. As in the continuous field case with zero entrance phase, only the odd harmonics are produced [12], but with significant redshift. The higher order harmonics have greater frequency shifts, and all harmonics shift more at higher intensity.…”

“…is different from the initial phase that the electron sees when it enters the field, which we denote as the entrance initial phase or entrance phase 0 !t 0 ÿ k rt 0 . 0 has been shown to have significant effects on Thomson scattering in a continuous field [12,14]; however, in a pulse field, its role has to be weighted by the pulse function ft ÿk r=c. The detailed analysis will be presented in the section Phase dependence.…”

Scale invariance and scaling law of Thomson backscatter spectra of electrons moving in the resonance regime in combined laser and magnetic fields

“…Different from the former works [23,24], our analytic solution of the motion equation indicates that the electron makes the strict periodic motion, therefore, the fundamental frequency of harmonic radiation would be affected by the combination of factors which include the period of the electron motion, the direction of observation and the electron orbit rather than only the laser frequency or the cyclotron-resonance frequency studied in Ref. [15,16]. On the other hand,it is found that the fundamental frequency of harmonic emission is independent of the initial phase of the electron with respect to the laser field, this point is contrast to the work by He [16].…”

“…Note that the dimensionless vector F(ω) can be expanded as an infinite series of delta function at the harmonics of the fundamental frequency of the emission spectrum [16] as…”

“…[31] demonstrates that the electron will emit radiation at high harmonics of the cyclotron frequency in the plane of the electron cyclotron orbit. Beside, when the cyclotron-resonance condition is met, i.e., the cyclotron frequency approaches to the laser frequency, the periodic motion electron makes would result in that the fundamental frequency of harmonic emission is neither the laser frequency nor the cyclotron frequency for the backscattered Thomson spectra [16]. Evenly the impact of cyclotronresonance degree of the electron motion upon the radiation spectrum can be adjusted by changing the electron orbit.…”