discovered_01_2016 - Illustration

TITEL // DAS FORSCHUNGSMAGAZIN AUS DEM HZDR WWW.HZDR.DE 08 09 L·A·S·E·R THE PUMPING MECHANISM The particles in the active medium have to be charged with energy. This can be done by an electrical discharge. What is crucial is that the "pumping" is so strong that more particles are in a charged state (red) than in an uncharged state (blue). This is referred to as population inversion. THE RESONATOR Two parallel mirrors ensure that the LASER beam is caught in the active medium. While the light moves back and forth it keeps gaining in strength by stimulated emissions – which is called positive feedback. One of the mirrors is partially light-transmissive: This is where the beam exits the LASER. TITLE // THE HZDR RESEARCH MAGAZINE THE ACTIVE MEDIUM The heart of the LASER: This is where the LASER beam is generated. The active medium is composed of many particles (blue and red balls), for example atoms of a gas which are mostly energetically excited (red). The particles can spontaneously discharge this energy by emitting a photon – as the portion of light is known. If the photon meets another excited particle , a stimulated emission occurs: an exact copy of the first photon is produced. The pair of photons that has now been created multiplies in a chain reaction which leads to light amplification. 1 2 3 1 2 3 Light Amplification by Stimulated Emission of Radiation WWW.HZDR.DE 08 09

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