help needed creating a focused laser beam

[emmanuelleroy]

Hello,

 

I'm trying to simulate an optical system which focuses a laser beam.

I would like to visualize the focused laser beam.

So, in reality the light would get focused with a lens. Some atmospheric effect would show the light being focused.

 

First, I wish there were spot or targeted lights that could be focused at some point, but there isn't any. I can make a parallel beam and design a real lens to focus the light, then use caustics and some atmospheric effect, but that seems like a whole lot of work to get this right, and my trials have been unsuccessful: either the light doesn't get focused the way i want of the lens is not doing it's job...

 

I thought of using 2 spotlights centered at the focus. the problem is that there is no way to properly cast shadows that way if one part of the beam is going in the wrong direction.

 

I tried using VRay's environment fog and structure it with an hourglass cone and using a light on one end, but here again it seems like the fog is illuminated wherever the cone is, no matter if an object casts shadows inside of it, plus the light doesn't look like it's coming from the focuses spot anyways.

 

I'm running out of ideas... The best to date seems to be to really simulate the parallel beam of light being focused by a lens

 

any tips from the pros here? I'm a newbie, i don't do this for a living! ;-)

thanks

[Tommy L]

Difficult to see what you're trying to do without an image. I think your beam may e easiest to do in post, Im aftereffects(animation) or photoshop (stills). To do a real simulation is maybe overkill if you're just illustrating something. Post an image, even a sketch, of what you are trying to achieve.

[Fooch]

Ditto for tom.

fix it post

[Tommy L]

Maybe look up a light saber tutorial.

[Tommy L]

But to do it in 3d I'd maybe look at a renderable spline in scanline with a self-illuminated material with a falloff in the opacity channel, then do some tests with scanline post-render glow.

[emmanuelleroy]

ok, here is a photo of the effect: a laser beam focused by the lens into a cuvette (middle rectangle) fulled with Rhodamine 6g (a fluorescent liquid that lights up where the beam enters it)

don't mind the arrow pointing at the dot, this is not my picture. Look at the yellow beam of light focused inside the red fluorescent materials in the top 1/3 part of the rectangular cuvette. This is what I'm trying to achieve.

2 spots going from the center in opposite direction will do this, but then shadows are wrong (see other picture that shows the correct way here:

https://skydrive.live.com/redir.aspx?cid=fbb88d70c742a380&resid=FBB88D70C742A380!148&parid=FBB88D70C742A380!110&authkey=!ANhDn8GUBHEVlTM)

 

Caustics will kinda create that effect, but then the fog is another issue: it varies with the camera position, and I haven't been able to figure how to avoid this.

I've tried to use some translucent material instead of fog to contain the effect (kinda like the liquid in the cuvette in the first photo, but clear this time so it doesn't show unless illuminated, but i've have little luck so far.

 

So in short: 2 different issues: the lighting part to generate the effect of the focused beam, and then the 'fog' or material settings to 'show' the light.

 

In a static image I can probably 'fake' it with some translucent object, but when things come in and out of the beam, tracking with proper shadows in a nightmare...

Edited April 30, 2012 by emmanuelleroy

[Tommy L]

So this is for animation or still?

[Nic H]

use a standard 3dsmax direct light (with a really tight focus) in conjunction with volume light

renders fast and you can beam control falloff and distance attenuation easily

[emmanuelleroy]

Ok, but how would i actually 'focus' the beam?

You guys in the CG world have your terminology backwards and call a 'focused' beam what really is a parallel beam. Focus means light rays converge into one point. That's what I want to achieve, and there doesn't seem to be any easy way to do this with 3ds.

If it was possible to somehow 'structure' or 'texture' the volume light effect, that might work...

[Nic H]

in that case i would use geometry then - its going to be much more flexible and easy to manipulate / animate to your needs.

it shouldn't be too hard to make a material for that either - then you can also render masks and tweak the appearance.

 

the only way to do it 'correctly' would be to use caustics and im not sure even maxwell or vray can do this with a degree of control!

[emmanuelleroy]

Don't know Maxwell but the name sounds like it might do the job right... I'll see if i can get access to a machine with it.

Maxwell equations are the basic equations of light behavior. Hopefully the program stands by its name!

 

 

following up. I got some so-so results with caustics in VRay. The beam focsuing in looks ok, but the light moving away from the focus point doesn't show.

It may actually be a fog issue: is there an actual way to use EnvironmentFog that is not affected by camera position?

 

Otherwise, I got the best results using an array of 100 spot lights over the area of the lens, and focused on the same spot...

However, i see 'rays' (see picture attached) and if i make the spot a 'disk', then it just doesn't work in the EnvironmentFog or VolumeLight for some reason, even if i crank up the intensity 10^12 or some crazy number. Any idea why?