how to make a laser?

[v_mulligan]

Hey, my hat's off to you OnoSendai. In theory, this ought to work -- but I'm glad to see it works in practice, too. And this is the sort of thing you really can't do with any other type of renderer.

[v_mulligan]

Heh heh. Fun with bouncing lasers off of things. Bzap.

[Kram1032]

cool
*waiting for more samples*

I wonder if you could also create a semi-reflecting mirror? (Not the variant of using a perfect mirror, blended with NULL, but an actual "real" semi-reflecting mirror...)

[v_mulligan]

Do you mean a beam-splitter? That is, something that will transmit a fraction of the light and reflect the rest? Or do you mean a dichroic mirror -- something that will transmit light of certain wavelengths and reflect light of other wavelengths?

[alex22]

Whats the problem with the Null?
A real semi reflecting Mirror reflects photons either to the right or to the left. The Null thing splits the ray in two rays with each having half of the former energy.

[v_mulligan]

Whats the problem with the Null?
A real semi reflecting Mirror reflects photons either to the right or to the left. The Null thing splits the ray in two rays with each having half of the former energy.

That's why I asked the question above. It seems to me that if you just want to make a beam-splitter, blending a perfectly reflective material with a NULL material is exactly the way to do it. If you really want to be accurate, you could add a small amount of an absorbing material as well. (Any material that transmits light will absorb a small amount).

[v_mulligan]

Excellent, how about using a lens now

The math is a bit more complicated for a lens, since the focal position is dependent not only on the shape of the two sides of the lens, but also on the index of refraction of the lens material. I believe (though I'm not 100% sure) that each side of the lens should be an arc (not a parabola). The lensmaker's equation is:

1/f = (IOR - 1) (1/R_1 - 1/R_2 + (IOR - 1)*d/(IOR*R_1*R_2) )

Where f is the focal length, IOR is the index of refraction of the lens material (relative the surrounding medium), R_1 and R_2 are the radii of curvature of the lens faces away from and towards the focus, respectively, and d is the thickness of the lens at its midpoint.

Maybe I'll try making a lens-based "laser" in the next few days.

[v_mulligan]

Correction: an arc is generally a good approximation, but it will lead to spherical aberration. I'm not sure if the correct shape is a parabola or a hyperbola...

[v_mulligan]

Hmm... I can't seem to find information about the perfect lens shape online. I'll check my physics textbooks when I get home, or derive the equations for the geometry myself.

In any case, I'd say the easiest and fastest way to do a perfect or near-perfect laser in Indigo is with a parabolic mirror, not a lens. (If anyone has ever wondered why the best telescopes are reflectors and not refractors, this is part of the reason.)

[Kram1032]

http://en.wikipedia.org/wiki/Aspheric_lens

Probably, both give interesting results... Though not the same ones, for sure^^

What's about a direct triple lens compare?

spheric |wall| hyperbolic |wall| parabolic

both convex and concave, as well as doublerounded () or singlerounded |) (no idea if that's the correct vocabulary for what I mean, but I hope, you know what I mean...)

[alex22]

The reason we have reflector Telescopes is because they are waaay easier to produce that lens telescopes. It would be so hard to produce a lens with several meters in Diameter.
btw I remember lens being hyperbolic.

[v_mulligan]

The reason we have reflector Telescopes is because they are waaay easier to produce that lens telescopes. It would be so hard to produce a lens with several meters in Diameter.
btw I remember lens being hyperbolic.

That's definitely part of it -- you can make a mirror much bigger than a lens. The other thing is it's easier to grind the perfect shape of mirror (a paraboloid) than it is to grind the perfect shape of lens (some sort of aspherical thing -- not yet sure what). Finally, one big problem with lenses is chromatic aberration. Any real-world material will have different indices of refraction for light of different wavelenghts.

Of course, with Indigo, we can work with "perfect" materials with identical IORs at all wavelengths. Given a decent modelling program, we can also make "perfect" lenses, provided we can derive the right equations defining the geometry. I'm kind of tempted, now, to try to make a "perfect" lens...

It might be fun to play with Fresnel lenses, too...

[CTZn]

both convex and concave, as well as doublerounded () or singlerounded |) (no idea if that's the correct vocabulary for what I mean, but I hope, you know what I mean...)

Well if YOU understand what you mean, why don't you do it ?

[v_mulligan]

http://en.wikipedia.org/wiki/Aspheric_lens

Probably, both give interesting results... Though not the same ones, for sure^^

What's about a direct triple lens compare?

spheric |wall| hyperbolic |wall| parabolic

both convex and concave, as well as doublerounded () or singlerounded |) (no idea if that's the correct vocabulary for what I mean, but I hope, you know what I mean...)

It's always best to start with the simplest possible system and to add elements only as needed. With three lenses, I have too many degrees of freedom. With a single lens, the only things I have to worry about are varying the shape of the front and the back (and to make things even simpler, I'll try and keep both sides the same shape). I just want to get parallel light rays to converge to a point, perfectly.

In cameras and telescopes, this is often done with multiple lenses in order to correct for distortions. Here, I can give a lens any properties I want to, though, so I might as well try and do this with a single lens.

[v_mulligan]

Oh, wait -- I misunderstood. You mean setting up three separate lenses, each with their own source, to see what sorts of geometric aberration each one causes? Yes, that might be interesting. It would be a little problematic, though, since I only know how to calculate the focus for a spherical lens at the moment...