Enhanced soft x-ray betatron radiation from a transversely oscillating laser plasma wake

Betatron radiation from relativistic electrons accelerated by a laser plasma wakefield is a promising x-ray source. However, the betatron photon number and energy is limited by the MeV electron energy when accelerated by a sub-terawatt laser pulse. Here we have proposed a scheme of enhancing the betatron radiation of electrons accelerated by a millijoule laser pulse. By applying a moderate mid-infrared control laser field, the plasma bubble and electrons injected inside are forced to oscillate transversely at a high, tunable frequency, enhancing the betatron oscillation strength and resulting in soft x-ray radiation.