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Laser beams are usually not cylinders of light, but instead they have a smooth beam profile, where they are brighter in the center of the beam and dimmer towards the sides. The cross section typically looks like a Gaussian function, do they are often called "gaussian beams".

Consequently, in illustrations, the lasers are often rendered such that they are most intense in the center and fade out towards the sides. I have achieved this using a blur effect in the compositor, but since Blender can handle most of the other physics in the world, I would like to include realistic laser beams directly.

Here is what I have come up with so far, but I am not quite happy with the results:

enter image description here

The blue beam was created using the node layout described in this post, except that I swapped the order of the colors in the color ramp. This still displays very sharp edges and they do not match the natural background color.

enter image description here

For the green beam, I tried to do the most realistic thing possible: I combined a volume emitter with a volume scatterer object. In reality, it is the scattering of the laser beam by particles in the air that allows us to see the beam, so I thought that this was the most appropriate. I added a set of nodes (yellow) to control the longitudinal intensity of the emitter in order to make the beam brighter near the focus (right side). Then, I included a set of nodes (red) to control the radial intensity of the beam in order to give it a nice soft edge. However, I just scaled the intensity along the radial coordinate, but did not take into account the fact that the beam is getting smaller. So, there is a nice gradient of intensity near the left side of the beam, but it's still very sharp towards the right side.

So, I suppose the question is how do I scale the intensity of the emitter while taking into account the width of the beam?

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Here is a node setup that approximates the Gaussian beam.

  • normalize the coordinates of the object by division on the dimensions
  • subdivide the radial dimensions "in this case Y and Z" on the beam length "X"
  • feed Y Z into a Gaussian function to create the redial gradient
  • the longitude gradient is simple (beam length-X)

cycles node setup for Gaussian laser beam

Coordinates node group
Coordinates node group

Gaussian function node group
Gaussian function node group
The A input in the Gaussian function group controls the amplitude of the Gaussian function.
S_y and S_z control the Y and Z spread.

simple render :example render

another render :

enter image description here .blend file
YA render

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  • $\begingroup$ Wow! i'm going to try and (i hope) understand this! thx! $\endgroup$
    – Bithur
    Feb 13, 2015 at 15:58
  • $\begingroup$ changing the object's origin allows to define where is the thinest point. (can be one side or in the middle giving 2 cones of light) $\endgroup$
    – Bithur
    Feb 13, 2015 at 16:35
  • $\begingroup$ @Bithur yes if download the file you can see that i have moved the origin to the end of the object , and it won't give two cones unless you take the absolute value of X $\endgroup$
    – Chebhou
    Feb 13, 2015 at 16:37
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    $\begingroup$ really fun!! now, question coming :) $\endgroup$
    – Bithur
    Feb 13, 2015 at 16:41
  • $\begingroup$ Thanks for demonstrating how to implement the gaussian function - that is awesome. But are you taking into account that the width of the object is changing with x? It seems that you have the same problem that I did, where you are defining a width of the gaussian that stays constant regardless of how the object changes in x. $\endgroup$
    – DanHickstein
    Feb 15, 2015 at 22:20

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