Area laser light missing in viewport render

[Burk]

Blender 2.79b, LuxCore 2.0

I have a project to show geometric optics with area laser light.
Here a sample for a laser from above meeting a glass slab:

That works fine with rendering (F12), but doesn't work with viewport rendering (Shift + Z).
s. blend-file attached
How can I get the preview in viewport rendering?

B.t.w. is there a description what exactly the parameters of volumes do? E.g. priority?

[B.Y.O.B.]

That works fine with rendering (F12), but doesn't work with viewport rendering (Shift + Z).

The viewport always uses the RT Path CPU engine, which is not able to compute the complicated light paths in your scene.

B.t.w. is there a description what exactly the parameters of volumes do? E.g. priority?

Not yet.
Volumes with a higher priority replace volumes with lower priority in areas where they overlap.

[B.Y.O.B.]

Just remembered we actually have a wiki page about the volume settings thanks to Piita.
However, the priority parameter is not yet described there.
https://wiki.luxcorerender.org/LuxCoreRender_Volumes