lasers use excited atoms or molecules to amplify light.
Free-electron lasers (FEL) use a high-energy electron beam as an
The electron beam emits light as it wiggles through a periodic magnetic
structure called undulator. The light is stored in in an optical
cavity, and can interact back with the electrons. This interaction
leads to a modulation of the electronic density, and a growth in
intensity and coherence of the emitted light.
The radiated wavelength depends on the energy of the electrons, the
undulator period and the applied magnetic field. In principle, any
wavelength can be produced from X-ray to THz. But most FEL up
now operate in a wavelength range spanning from UV to far-infrared.
Limitations occur mostly from the electron beam quality and of course,
the cumbersomeness and price of the required particle accelerators.
A different laser
- Undulator radiation