Thu, 12 Dec 2019

Maccabeam™ Part 5: Oil and Lasers

— SjG @ 1:00 am

Part 1: Simulating candle-light with pseudo-random sequences
Part 2: Some physical structure
Part 3: When Exactly is Hanukkah?
Part 4: A Typical Programming Problem

So, remember how the one of the original requirements was that the lasers would illuminate vials of olive oil? Now that I’m at the point where I have the lasers working, I’ve discovered that olive oil is more transparent than I anticipated. In my mind, I kind of saw the oil illuminating evenly from the laser light when, in fact, it just creates a single faint beam like this:

Laser illuminating a full vial of oil

So, I could see that I got nice reflection and illumination off of the air-oil boundary up top, so the next thing I tried was filling the vial only partially:

Laser illuminating a partially full vial of oil

That’s better, but still lacks something. The next idea was to mix some very fine glitter into the oil:

Laser illuminating a partially full vial of oil with glitter

I like this! I think it looks really nice, but there’s still a problem. The glitter lamps and lava lamps that inspired this approach use convective forces to keep the glitter or wax moving inside the lamp. In my system, the laser light doesn’t transfer any measurable thermal energy to the oil, which means that there is no convection or other currents in the oil. So it looks good for a while, but as the next video shows, after ten minutes, we’re pretty much back to just a vial of oil — but with a clump of glitter on the bottom occluding the light.

Ten minutes later: Laser illuminating a partially full vial of oil with glitter

So how do you make it so glitter doesn’t sink to the bottom of the oil? Introduce thickeners! In this case, I blended in some corn starch, carefully heating it for maximum absorbtion. Now, not only is this getting way away from the original idea of illuminated oil (corn starch in the menorah probably violates halacha somehow), but I was unable to do it in a way that didn’t just cloud up and look icky.

Laser illuminating a partially full vial of oil, corn starch, and glitter

Not only does that look like a distressing medical sample, it still suffers from the same problem. The thickener slows the sinking of the glitter, but doesn’t prevent it entirely. After half an hour, it’s just murky soup:

Half an hour later: laser illuminating icky blend of corn starch and oil.

Going back to the observation from the beginning, I’d got nice scattering from the interface of the oil and the air. Maybe I’d get the same nice scattering from an interface between crystal and the oil. So I filled the vial with a few faceted bits of crystal to see:

Laser illuminating a vial containing oil and crystal beads

It’s a lot nicer than the oil/corn starch blend, but still not spectacular. Still, it fels like moving in the right direction. The last experiment was to fill up the vial with small beads made of ordinary glass and the oil. I chose 11/0 (2.2 mm) beads, thinking smaller beads meant more interfaces for scattering:

Laser illuminating a vial of glass beads and oil

Finally! While it’s not perfect, I like this look, and the source of the light scattering will not sink into oblivion any time soon. Coming up with an explanation is a little harder. Do the beads represent the sands of the Judean desert? Shattered windows of the Second Temple? Did they even have glass windows at that time? Well, regardless of explanation, this is what I will use for the final version.

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