Free Electron Lasers Explained With Diagram

Lasers have always been a subject of interest for students of modern physics. And why not, lasers are known for their accuracy and power. The free electron lasers are very similar to the conventional lasers but the mechanism used to produce coherent electromagnetic radiation is different in case of free electron lasers. Unlike the conventional lasers in which a gas or solid is used as the lasing medium, the electron beam is used as the lasing medium in free electron lasers (FELs). FEL was invented by John Madey at Stanford University.



In FEL, the electron beam is first passed through a linear accelerator in which the beam is accelerated to a speed which is nearly equal to speed of light. Then the accelerated beam is passed through an oscillator (also called as a ‘wiggler’) , formed by an array of magnets with alternating poles.  Under some specific conditions the electrons bunch together tightly and they begin to oscillate. In some cases it might be required to pass the electrons back and forth through the oscillator. The electrons follow a sinusoidal path. The motion of the electron is in phase with the light already emitted and this causes coherent emission of light. Thus, instead of emitting light independently, the electrons emit light in phase with each other. This light emitted has characteristics similar to that of a conventional laser. Wavelength of the emitted light can be changed easily by changing either the electron beam energy or the magnetic field strength or both. The light generated comes in ultrashot pulses due to the small size of electron bunches. The light emitted in oscillator can also be used to generate new electrons and thus making the FEL more powerful. The wiggler can also be placed in an optical cavity formed by mirrors. The free electron laser has widest frequency range including microwaves , infrared , visible sprectrum , ultraviolet and terahertz radiation also.

Free electron lasers have a wide range of applications in the field of optics, medical science and military. FELs can be used in operating  upon brain, cornea and skin tissues.  Dr. Rox Anderson of the Wellman Laboratory of Photomedicine predicted possible medical application of the free-electron laser in melting fats without harming the overlying skin.FELs have a very deadly accuracy in shooting down cruise missiles. USA’s navy has conducted experiments in which FELs were used to cut steel at rate of 20 feet per second. After few years lasers might replace bullets.