Dispersion of Laser looks odd

[FarbigeWelt]

In my opinion Laser with monochrom color like RGB 255,0,0 shouldn't disperse but it does, see attachments.
BiDir

macos: Ventura 13.2.1
Blender: 2.93.18 LTS
Luxcore: 2.6

[FarbigeWelt]

Without dispersion Laser looks correct.

[FarbigeWelt]

In the scene there is large cube with inside volume homogenous.
The bodies like the cone, the lenses have an outside of volume clear like air.
The different volumes have defined priorities,.e. g. volume air 0 and volume homogenous 10.
But the priorities of the volumes seem not working properly.
For the pictures above I had to change all outside volumes to homogenous.
I expected, maybe wrongly, that in case of overlapping volumes, the higher priority bats the lower.
But this works obviously not perfectly.

Due to much noise png file is to large. I add a smaller picture later.

[FarbigeWelt]

There is a further issue.
Look at the right border of the picture.
The picture doesn't fit correctly there is border because the picture shifts some pixels to the right after rendering.

EDIT:
After setup a new Blender file by appending Objects in a new Scene this odd rim disappeared.
However this happened it had nothing to do with with LuxCore.

[FarbigeWelt]

Path rendering without cache

Path rendering with caches

How ever there is quite a difference in the background compared with bidir rendering.

[FarbigeWelt]

Just for the fun of it I've setup a more famous scene setting.

BiDir and Metropolis, no chaches

BiDir and Metropolis, some chaches

Path with Light tracing, no caches

Path with Light tracing, some caches

Unfortunately the Blender file is too large I guess I should zip the file first. I may post it later.

[FarbigeWelt]

Cornel Box copy.blend.zip

(449.12 KiB) Downloaded 166 times

[FarbigeWelt]

I think a lot of question repeat about Glasses and Homo- or Heterogeneous Volumes.
A most tricky one, rendering an orange juice even required user with lots of experience to solve the question.
For the simplicity I attached here a Bender with a special Cornell Box containing a Glass of wine and one with juice.
Very important is to work with Volumes in case of glasses or liquids.
Don't change the color in then material because that won't work that means it works but not as expected.
Glasses and other Liquids must have a proper Interior Volume that means one can use fully saturated colors. The colors' depth are defined with Absorption.

Very low scattering

More scattering air volume. One has to set the volume for camera, the world and for each object inside the foggy box the Exterior Volume.

Cornel Box Kopie.blend.zip

(1.85 MiB) Downloaded 111 times

[FarbigeWelt]

As one can see there are differences between BiDir and Path Rendering.
With BiDir the orange juice looks like orange juice but with Path it doesn't.
What both algorithms fail is to render scattered lights behind Glass.

I don't know how scattered light is calculated. If light generates new Point Lights for each particle it hits then the scattered light should be visible even behind glass or in the mirror I guess. The bouncing counter still applies.
Actually creating a new light for each bouncing until the camera is hit or the counter is down to zero I mean the light dies after the number set for path depth.

[rrubberr]

Have you tried rendering it with LuxCore's BidirVM integrator and Metropolis sampling? Vertex merging would be a good fit for this scene.