Tunable radiation source through upshifting without ionization

A mechanism for generating electromagnetic wakes of infrared radiation by a short laser pulse, propagating through an underdense plasma in the presence of a magnetostatic undulator, is described. As opposed to the undulator radiation, produced when a charged particle bunch propagates in a periodic magnetic field, here a laser pulse is used instead of the particle bunch. This mechanism for a tunable, plasma-based radiation source does not rely on ionization or photoswitching. It is also found that, in the presence of a static periodic magnetic field, long laser pulses become modulationally unstable, generating an electromagnetic wake.