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Heat distribution of an infrared focused laser beam

Posted May 10, 2012, 2:21 a.m. EDT Heat Transfer & Phase Change, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.2a 2 Replies

Jakrey Myers
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Hi all,

I am looking to model the localized heating of a focused infrared beam. In specific I am looking to model a 1064nm optical trap, given the absorption of the trapping medium and the power of the beam.

The assumption I make is that all absorption events are dissipated through heat which is likely reasonable at these frequencies. I would also like to make this a transient model in the future, however I am suffering from fundamental problems.

I model the intensity profile of the beam, which seems to work out well. However when I couple the absorption (attenuation) coefficient as the heat induced I am encountered with non-physical temperatures.

Am i missing something simple or is my assumption just fundamentally wrong?

Thanks in advance
Jakrey Myers
2 Replies Last Post May 10, 2012, 3:27 a.m. EDT
Jakrey Myers
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Posted: 1 decade ago May 10, 2012, 3:10 a.m. EDT
After realizing COMSOL not liking my wz parameter expression I created an analytical version and was confronted with some new errors.

File attached

Thanks in advance
Jakrey
After realizing COMSOL not liking my wz parameter expression I created an analytical version and was confronted with some new errors. File attached Thanks in advance Jakrey
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 10, 2012, 3:27 a.m. EDT
Hi

first of all your wz is not a parameter, but a variable, remove it from the "parameter" section and add a Definition variable
and add it therein.

Then I'm astonished from the heat flux shape, if you add a 2D plot, Surface plot with the ht.Qtot COMSOL variable, then turn on wireframe and add a height Expression subnode, you will see that you deposit your energy really only over a few mesh elements, either you have a typo in your formula, or you need to encircle that region and use a much finer mesh therearound, and use a coarser one outside.

It is often usefull to set such formulas as for your heat flux into an anlalytical expression as you can then easily plot it and check that its coherent with your wish

--
Good luck
Ivar
Hi first of all your wz is not a parameter, but a variable, remove it from the "parameter" section and add a Definition variable and add it therein. Then I'm astonished from the heat flux shape, if you add a 2D plot, Surface plot with the ht.Qtot COMSOL variable, then turn on wireframe and add a height Expression subnode, you will see that you deposit your energy really only over a few mesh elements, either you have a typo in your formula, or you need to encircle that region and use a much finer mesh therearound, and use a coarser one outside. It is often usefull to set such formulas as for your heat flux into an anlalytical expression as you can then easily plot it and check that its coherent with your wish -- Good luck Ivar

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