Undulator

An undulator is an insertion device from high-energy physics and usually part of a larger installation, a synchrotron storage ring, or it may be a component of a free electron laser.

Electrons traversing the periodic magnet structure are forced to undergo oscillations and thus to radiate energy.

The radiation produced in an undulator is very intense and concentrated in narrow energy bands in the spectrum.

the oscillation amplitude of the motion is small and the transverse deflection nearly sinusoidal as a function of time, so that long undulators can have narrow on-axis bandwidth, and most of the radiated power at around the fundamental wavelength.

the oscillation amplitude is large and the transverse deflection is no longer sinusoidal in time so that it contains Fourier components of high harmonics of the fundamental wavelength.

[2] Since the radiation emitted from an undulator is incoherent, the power scales linearly with the number of electrons.

The polarization of the emitted radiation can be controlled by using permanent magnets to induce different periodic electron trajectories through the undulator.

The Russian physicist Vitaly Ginzburg showed theoretically that undulators could be built in a 1947 paper.

[3] Julian Schwinger published a useful paper in 1949[4] that reduced the necessary calculations to Bessel functions, for which there were tables.

The design could produce a total frequency range from visible light down to millimeter waves.