Backscattering 1 Backscattering spectra 1 Electron dynamics 1 Electrons 1 Even orders Gaussian distribution 1 Gaussian lasers 1 Harmonic analysis 1 Harmonic generation 1 Harmonics generation 1 Intensity distribution 1 Laser pulses 1 Ponderomotive forces 1 Symmetry breakings 1 Thomson 1 Thomson backscattering 1