Imagine a laser that is continuously tunable over a wide range of wavelengths, including wavelength domains where conventional lasers cannot operate. This new kind of laser has already proven itself at microwave, far-infrared, visible, ultraviolet, and even x-ray wavelengths. Furthermore, it can run reliably and efficiently for days, or even weeks, with only minor maintenance, producing anything from continuous-wave laser light to subpicosecond pulses.
What we’re describing is the free-electron laser. FELs contain only the essential ingredients for light amplification by stimulated emission: a beam of electrons, an external magnetic field to deflect them, and laser light. They dispense with nonessentials like the atomic nuclei and their bound electrons that impose limitations on conventional atomic lasers. The gain medium of the FEL is transparent to all wavelengths, and the physics of the gain mechanism is essentially the same for all wavelengths from a centimeter down to an angstrom.
The FEL...
