[FLASH-USERS] Variable "absr" in FLASH Output

[David Montgomery]

Hi Owen & user-group,

I couldn’t find anything about “absr” either in the documentation.

But the “lase” plot variable, only available when doing 3D-in-2D ray tracing I believe, is energy density of the available laser energy at any given point in space, in units of ergs/cm^3.

We use “lase” frequently and convert it to laser intensity in W/cm^2 using:

“lase” * V_group * 1.0e-7 J/erg

where V_group is the group velocity of the laser in the plasma, V_group = c * sqrt(1 - wp^2/w0^2) = c * sqrt(1- ne/ncrit), the speed of light times the refractive index of the laser in the plasma.

Beyond that, LaserEnergyProfile.dat will at least give you time dependence and time integrated laser energy coming in and going out.

Hope this helps.

David


> On Aug 12, 2025, at 11:53 AM, Owen Bardeen <owenbardeen at gmail.com> wrote:
> 
> Hello all,
> 
> I'm trying to get a good idea of laser absorption in my FLASH simulation. I know I have access to the LaserEnergyProfile.dat file as well as the energies and "lase" variable in each cell in FLASH output to help understand this. 
> 
> I see the "absr" variable as another output, and intuitively it would make sense for it to be some kind of quantification of laser absorption, but I don't see any documentation on what it is or its units. I can't quite determine it myself. 
> 
> Can someone help me understand the "absr" variable and its units? General advice for analyzing laser absorption would also be greatly appreciated.
> 
> Thank you!
> Owen
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