The free-electron laser has the widest frequency range of any laser type , and can be widely tunable , currently ranging in wavelength from microwaves , through terahertz radiation and infrared , to the visible spectrum , ultraviolet , and X-ray .
The free-electron laser has the widest frequency range of any laser type , and can be widely tunable , currently ranging in wavelength from microwaves , through terahertz radiation and infrared , to the visible spectrum , to ultraviolet , to X-rays .