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The Ideal Pump Intensity Distribution in an End-Pumped Solid-State Laser

Posted on 2007-04-01 as a part of the Photonics Spotlight (available as e-mail newsletter!)

Permanent link: https://www.rp-photonics.com/spotlight_2007_04_01.html

Author: , RP Photonics Consulting GmbH

Abstract: One often comes across the question what shape and size of pump intensity profile is ideal for an end-pumped laser. The article shows that a universal answer can not be appropriate: what is best depends on many different aspects. For solid-state lasers operating at higher power levels, a laser design based on a careful analysis can replace a tedious trial-and-error approach.

Dr. Rüdiger Paschotta

Ref.: encyclopedia articles on end pumping, side pumping, thermal lensing, beam quality, resonator modes, mode coupling, and alignment sensitivity; R. Paschotta, “Beam quality deterioration of lasers caused by intracavity beam distortions”, Opt. Express 14 (13), 6069 (2006)

In the scientific and technical literature, one often comes across the question what shape and size of pump intensity profile is ideal for an end-pumped laser. The given answers vary quite substantially and sometimes even appear to be in outright contradiction with each other. I suppose that many people would like to know what the right answer is.

Here it is: it depends! I am sorry, but that's true, even if we consider only lasers with diffraction-limited (TEM00) output:

In this context, it can be important to understand how exactly aberrations influence the laser's beam quality: via mode coupling – see the paper cited above. Interestingly, this crucially depends not only on mode sizes in the laser crystal, but also on other properties of the resonator design.

So we see that a universal answer cannot be appropriate. To find out what is best in a concrete case will often require either a carefully worked out approach, based on the detailed understanding of the relevant physical issues, or an experimental trial-and-error approach which might be tedious and result in non-ideal performance or stability. There are, however, cases e.g. where only a low output power is required, and the design is not critical.

In any case, however, it is highly recommended to carefully check the pump intensity profile e.g. with a beam profiler even before building the laser resonator. By trying to save a little time at this point one may later on get into trouble e.g. with instabilities, and it takes much longer then to identify and cure the cause.

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 RP Photonics Encyclopedia.

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