how to make a laser?

CTZn · Post by **CTZn** » Tue Jan 27, 2009 10:42 am

Thank you for that great input, v_mulligan !

Lord of the Rings Junkie · Post by **Lord of the Rings Junkie** » Tue Jan 27, 2009 1:49 pm

v_mulligan wrote:If you were to make a lasing cavity in Indigo, you wouldn't get a laser out. There's no way for Indigo to simulate stimulated emission from a medium.

Thank you, this is what I was trying to communicate.

I'm conducting my own tests right now.

Lord of the Rings Junkie · Post by **Lord of the Rings Junkie** » Wed Jan 28, 2009 3:04 am

Well, I'm getting close. I'll have to tinker some more to get the collimation tighter, though.

The width of the peg at the wide end of the beam is the target beam diameter at 1 meter. I'm using a set of two lenses to collimate, but it seems VERY sensitive to the shape and thickness of the lens. I've resorted to making fine adjustments to the IOR of the lens material itself, so we'll see how it goes.

Once I get good collimation, the next step will be acceptable power. The render you see uses linear tone mapping with a scale of 5*10^9!

v_mulligan · Post by **v_mulligan** » Wed Jan 28, 2009 6:11 am

Oh, okay -- you're using a lens-based collimator. When you said "collimator" I was thinking of the sort used for x-ray beams -- a tube with a grid in it (see http://upload.wikimedia.org/wikipedia/c ... imator.jpg). My concern with that was, of course, that most of the light would be absorbed, but you won't have that problem with lenses.

If you're using lenses, the lensmaker's equation might help you (see earlier post) to figure out where to put the light source relative the lens. Note that that's for a lens with an arc-shaped cross section (i.e. a spherical lens).

Zom-B · Post by **Zom-B** » Wed Jan 28, 2009 6:42 am

Lord of the Rings Junkie wrote:The render you see uses linear tone mapping with a scale of 5*10^9!

Light normalization ftw!!!

Try to define your lasers flux by your self, if you don't, Indigo does! And the smaller your lightsource, the smaller the flux Indigo uses for this light!

a flux of 10000 is me fine with the most tonemapping like camera & linear... but camera settings are important here too... f-stop & Co...

Lord of the Rings Junkie · Post by **Lord of the Rings Junkie** » Thu Jan 29, 2009 12:10 pm

I'm continuing my tests, but I thought I would provide my .blend file so that other people could take a crack at making a lens collimator as well. The following render shows the raw, uncollimated beam emerging from a 0.5mm aperture with a divergence of approx. 3.5 degrees. The peg at the target indicates the desired beam width of about 2mm at a distance of 1 meter from the aperture. The collimating lenses should probably have a diameter of about 2mm as well.

Layer 1 of the blend file contains several cameras and fog to make the beam show up. Layer 2 contains the laser itself and the target geometry. Let's see who can do it first...

CTZn · Post by **CTZn** » Fri Jan 30, 2009 4:20 am

The best collimation results I've seen with indigo were from high res paraboloid reflectors I think...

Kram1032 · Post by **Kram1032** » Fri Jan 30, 2009 6:37 am

Hmmm... In theory, a laser is built like that:
two mirrors, one being (more or less) 100% reflecting and the other one being like a semi-mirror, letting 50% through and reflecting the other 50%. (In reality, it's impossible to get a 0-absorber, so a tiny amount of light always gets absorbed...)

Using twice a specular mirror with IoR 1000 or so and blending one of them with NULL at blendfactor 0.5 should work fine...

between, you need a black diffuse tube.... and if you want to maximize your emission energy, you probably need to shape the "backside" mirror like a parabola....
The emitting ball should be in the focal-point and besides being an emitter, you might want to also make it a diffuse white (in this special case 1 1 1 white) material, so that it throws back all the rays, hitting the side on the parabola...

eulgrand · Post by **eulgrand** » Fri Jan 30, 2009 7:57 am

Call me lazy

Kram1032 · Post by **Kram1032** » Fri Jan 30, 2009 8:10 am

you know, that's actually NOT what you'd want. you'd actually want a lightsource, emitting on the whole (parabolic) mirror, to get a wider beam PLUS less wideing (namely, if it's a pefect parabola, ZERO)

eulgrand · Post by **eulgrand** » Fri Jan 30, 2009 8:41 am

I agree with you Kram. The IES may be a good starting point though, acting as a "perfect" cone, placed at the focal point of the parabolic mirror.

v_mulligan · Post by **v_mulligan** » Fri Jan 30, 2009 8:53 pm

Kram1032 wrote:you know, that's actually NOT what you'd want. you'd actually want a lightsource, emitting on the whole (parabolic) mirror, to get a wider beam PLUS less wideing (namely, if it's a pefect parabola, ZERO)

I did it already, exactly as you describe. See the bottom of page 2 of this thread and the top of page 3. And there's no challenge to getting widening if that's what you want; just move the light source in a bit from the focus of the paraboloid. If you want none, keep a point source right on the focus.

The new challenge is to do it with lenses instead of mirrors. The math becomes a bit trickier, especially if you want to figure out the "perfect" lens shape to avoid any spherical aberration from the lenses.

Kram1032 · Post by **Kram1032** » Sun Feb 01, 2009 12:33 am

Oh! I somehow didn't realice, that it's THAT old thread xD

neo0. · Post by **neo0.** » Sun Feb 01, 2009 8:35 pm

VERY neat stuff. Looking forward to future development on this.

galinette · Post by **galinette** » Thu Feb 04, 2010 11:28 am

This is a very old post but... LOTR : not so sure it's impossible to make stimulated emission in Indigo. Actually this can be not so badly described by a negative absorbance coefficient. Actually Indigo probably complaints when k<0 in a medium, but it's probably very simple to remove this constraint. Then it should be able to make simple optical amplifiers.

ANY light-matteer interaction (such as all phenomenons described in Indigo's material is a relation between light and electrons. Not only lasers.

Etienne

how to make a laser?

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