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The Photonics Spotlight

Higher Heat Generation Density, Stronger Thermal Effects?

Posted on 2007-07-25 as a part of the Photonics Spotlight (available as e-mail newsletter!)

Permanent link: https://www.rp-photonics.com/spotlight_2007_07_25.html

Author: Dr. Rüdiger Paschotta, RP Photonics Consulting GmbH

Abstract: One usually expects that the higher the density of dissipated power in a laser crystal is, the stronger are the resulting thermal effects. The article shows that in a thin disk laser this is not quite true: reducing the disk thickness increases the power density, while reducing thermal effects.

Dr. Rüdiger Paschotta

Ref.: encyclopedia articles on thin-disk lasers and thermal lensing

It is common wisdom (and seems pretty plausible) that the density of dissipated power in a laser crystal should be kept low enough to avoid excessive thermal effects, such as thermal lensing. In this light, it may appear unlikely that the concentration of the dissipated power in a rather thin disk of crystal material, as used in a thin-disk laser, is a good idea.

It is worth to consider what happens when e.g. the thickness of such a disk (made e.g. of Yb:YAG) is reduced to one half the original value, while leaving the total dissipated power unchanged:

So in total we have reduced temperature rises, and consequently also reduced transverse temperature gradients and thermal lensing, even though we have doubled the density of heat generation.

In conclusion, one should be a bit careful concerning the link between power density and thermal effects; geometry has an important influence.

This article is a posting of the Photonics Spotlight, authored by Dr. Rüdiger Paschotta. You may link to this page and cite it, because its location is permanent. See also the Encyclopedia of Laser Physics and Technology.

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