Electromagnetic radiation is found as a natural phenomenon in almost all areas of daily life. Some examples are thermal radiation (in the form of warmth), x-rays and γ-rays emerging from radioactive decomposition. Electromagnetic radiation is also artificially generated by radio transmitters or mobile phones. It travels in waves like sound and is produced by the movement of charged particles. In contrast to sound, electromagnetic radiation does not need a medium in which to travel. Laser radiation – like all light – consists of electromagnetic radiation as well.
Electromagnetic radiation within the range visible to the human eye is commonly called light. In this general sense light consists of electromagnetic radiation in the wave-
length range between 380 and 780 nm (nm = nanometer = one billionth of a meter). This range is designated as the visible spectrum. When all wavelengths in the visible spectrum are emitted simultaneously, this is perceived as white light. When white light falls on an optically dispersive element such as a prism or birefringent filter the colours of the spectrum can be seen due to refraction. It starts at the short wave as the colour violet, turning to blue, green, than yellow and goes to the long wave, which appears as red. Beyond the long wave (red) of the spectrum is the near and far infrared range. Below the shortwave range (blue) is the ultraviolet range.
But the term Laser-‘light’ refers to a much broader range of the electromagnetic spectrum: between 150 nm up to 11000 nm, i.e. from UV-‘light’ up to far infrared ‘light.’
