Continuing with the American Physical Society's milestone series celebrating 20th century achievements in physics, the 1976 milestone includes two letters that together detail the first experimental demonstration of a working free electron laser (FEL), in which a beam of unbound electrons is made to travel through a periodic magnetic field and generate a beam of light.
It's research that represented a major breakthrough in laser development: FELs held the promise of a widely tunable source of coherent radiation, something that had eluded researchers since the invention of "masers" in the 1950s. Both papers cover work done at the Stanford University High Energy Physics Lab. Using two different experimental setups-one which "seeded" the electron beam with a CO2 laser, and one which used a reflecting cavity-beams of coherent infrared radiation were created using the Stanford superconducting linear accelerator (different to the existing two-mile-long copper linear accelerator in use today).
Today, FELs represent the next big step in the use of synchrotron radiation for investigating matter down to the atomic scales of length and time. Several FELs are in operation around the world now, all based directly on the principles derived here. And FEL evolution continues, with more powerful electron beams and longer arrays of undulators producing wavelengths down into the X-ray range. In 2009, the Stanford Linear Accelerator Center will begin operation of the first FEL to create "hard" X-rays, with wavelengths in the ångström range, the Linac Coherent Light Source.
