What is an undulator?
Q: What is an undulator?
A: An undulator is a device from high-energy physics that consists of a periodic structure of dipole magnets. It forces electrons to undergo oscillations, which produces intense and concentrated electromagnetic radiation in narrow energy bands.
Q: What parameter characterizes the nature of the electron motion?
A: The important dimensionless parameter K = eBλu/2πβmecc characterizes the nature of the electron motion, where e is the particle charge, B is the magnetic field, β = v/c , me is the electron rest mass and c is the speed of light.
Q: How does an undulator compare to a bending magnet in terms of magnetic flux?
A: Undulators can provide hundreds of times more magnetic flux than a simple bending magnet.
Q: How does interference affect intensity when using an undulator?
A: If K ≤ 1, then oscillation amplitude is small and radiation displays interference patterns which lead to narrow energy bands. If K ≥ 1, then oscillation amplitude is bigger and radiation contributions from each field period sum up independently leading to broad energy spectrum.
Q: How can polarization be controlled when using an undulator?
A: Polarization can be controlled by using permanent magnets to induce different periodic electron trajectories through the undulator. If oscillations are confined to a plane, radiation will be linearly polarized; if trajectory is helical, radiation will be circularly polarized with handedness determined by helix.
Q: How does intensity increase with number of electrons for free-electron lasers?
A: When electrons follow Poisson distribution, partial interference leads to linear increase in intensity; for free-electron lasers intensity increases exponentially with number of electrons.
Q: What measure do physicists use to evaluate an undulator's effectiveness?
A: Physicists measure an undulator's effectiveness in terms of spectral radiance.
