Abstract
Free electron Lasers (FEL) have advantages of wide tunability, high efficiency and no lasing material which imply the high potentiality for various applications. However very low emittance of electron beam and high accuracy of wiggler magnetic field is required to obtain FEL oscillation. Recent progress of accelerator technology overcomes these issues and makes possible to obtain high power short wavelength FEL. We present the principal of FEL, its properties and system briefly. The applications for various field is also discussed.
