Lifting the Confusion Concerning Doping Concentrations

Posted on 2006-07-01 (revised on 2006-07-02) as a part of the Photonics Spotlight.

Permanent link: http://www.rp-photonics.com/spotlight_2006_07_01c.html

Author: Dr. Rüdiger Paschotta, RP Photonics Consulting GmbH

Ref.: encyclopedia article on doping concentration

There are quite a few different ways to specify doping concentrations in laser crystals and glass fibers. Unfortunately, it is very often not made clear which definition is actually used. As a consequence, doping concentrations are quite commonly seen as a kind of house numbers: the crystal with the higher percentage of doping is expected to absorb the pump radiation better (hoping that both specifications were based on the same definition).

Knowing what these numbers really mean allows one to do useful calculations. For example, one may predict the pump absorption efficiency before one builds up a laser. Quite obviously, this can be more efficient than a “trial and error” approach of ordering different crystals and taking those which work best.

To clarify the situation, RP Photonics has recently published a new encyclopedia article on the issue of doping concentrations.