Laser Microscope
September 7, 2010 1:11 PM   Subscribe

"After witnessing the image of a mosquito in a laser beam outside, I decided to investigate the phenomenon further. I started by locating scuzzy water. Ponds lacking, I decided to take water out of the bowl of my 6 year old spider plant. I then filled a syringe and hung it above a laser so that a drop of water, almost ready to fall, was in the beam path." [via]
posted by brundlefly (31 comments total) 46 users marked this as a favorite
Apparently the site's been up and down, so here's a mirror if needed.
posted by brundlefly at 1:12 PM on September 7, 2010

Note to self: Every visualization is better with a cat.
posted by null terminated at 1:13 PM on September 7, 2010 [21 favorites]

That's no moon.
posted by swift at 1:13 PM on September 7, 2010 [1 favorite]

Science cat is watching you investigate.
posted by Horace Rumpole at 1:14 PM on September 7, 2010 [32 favorites]

This is an important advance in cat entertainment.
posted by melissam at 1:20 PM on September 7, 2010 [21 favorites]

Holey moley! I know what I'm doing tonight.
posted by MrMoonPie at 1:24 PM on September 7, 2010 [1 favorite]

New bumper sticker:


posted by Halloween Jack at 1:33 PM on September 7, 2010 [2 favorites]

Wow, that's amazing.
posted by cryptozoology at 1:48 PM on September 7, 2010

That's cool, but are they really bacteria? It seems to me they might be larger organisms.
posted by Philosopher Dirtbike at 1:51 PM on September 7, 2010 [5 favorites]

This is awesome. Kinda makes me want to get my 9th grade biology teacher's email and send it to her.
posted by CrazyLemonade at 1:53 PM on September 7, 2010

I keep waiting for Science Cat to start adding his own MST3K style critiques.
posted by rokusan at 1:54 PM on September 7, 2010

Our cat Yorvit would love this. He loved the parkour video from the other day.
posted by rtha at 2:05 PM on September 7, 2010 [1 favorite]

Back when I used to do laser shows in the very early 90s I used to do this. You can do it a number of ways. Using a syringe without a needle is one way, but eyedroppers work fine too, as does stacking drops of water on the end of something thin like the inside of a pen.

You can also use dirty water with microbes in it or you can use dust, dirt, ash or other very fine particles suspended in water and Brownian motion happily keeps it all in motion.

It works because the surface tension of water is so high and it has such a heavy refraction index that it effectively makes lenses around any particles or microorganisms, and then the spherical shape of the water droplet acts as a "very short focal length convex lens" otherwise known as a "beam expander" in laser and optics circles - basically a magnifying glass with a focal length so short that it's located inside the lens itself.

I never could figure out how to incorporate it into the laser shows I was doing because it's so unstable, messy, subtle and not very bright at large sizes. Back then my most powerful laser was an 8 milliwatt helium-neon tube laser about three feet long that cost me about $300 in the day. 1-5mw diode lasers were still more expensive then that, and not as bright per mw due to the wavelength of diode lasers being closer to infrared then pure red. Point being - my projections and experiments were either very dim or had to be projected on a nearby piece of white paper at a much smaller size and closer distance.

Another thing that was cool about it is that it would react to sound and vibrations, which is an automatic win when you're doing laser shows for raves, but alas I never was able to bring it to a show because my lasers weren't powerful enough to project it large enough to be that interesting for an audience.

I would love to try to set this up again with an RGB laser projecting three beamlines, one color each for it's own droplet-lens, and then overlap the circles perfectly. The chaotic movements and distortions from each drop would cause some amazing RGB additive-color blending and displays.

But even in an art gallery it would be hard to keep it stable for very long. The small size needed for the water droplet to make it behave as a lens means that it evaporates quickly, on the order of an hour or two depending on humidity and even less if it's warm enough out, on the order of minutes, because you're talking about a droplet of water smaller than a BB. The droplets tended to go from near-spherical to flat (and out of the beamline) rather fast.

I suppose someone could use glycerin or something besides water - but there's nothing that has the particular surface tension that water has, and higher viscosity of something like glycerin would mean less Brownian motion.

Warning: If you try this at home be careful. I would be extremely careful if you used one of the higher power green or blue diode lasers. You're dealing with reflective surfaces and beam spreaders. Do not look into laser with remaining eye.
posted by loquacious at 2:15 PM on September 7, 2010 [18 favorites]

posted by schoolgirl report at 2:16 PM on September 7, 2010

Please ( do | do not ) try this with NYC tap water.

(I can't decide whether or not I want to know.)
posted by rokusan at 2:18 PM on September 7, 2010 [1 favorite]

posted by Senor Cardgage at 2:28 PM on September 7, 2010 [9 favorites]

I kept waiting for the cat to go medieval on those bacteria. Who needs white cells when you've got a kitty?
posted by CheeseDigestsAll at 2:43 PM on September 7, 2010 [2 favorites]

loquacious, I am fairly certain I could design a feedback system with a micropump to stabilize the droplet size. Take feedback from a second laser aimed across the path of the main display laser, project onto a CCD (or a screen viewed by a CCD or even a set of strategically placed phototransistors) and use something like a fine pitch screw driven by a servo to change the volume of the feed container.
posted by localroger at 3:18 PM on September 7, 2010 [3 favorites]

that reminds me way too much of the floaties i get in my eyes.
posted by msconduct at 3:31 PM on September 7, 2010 [2 favorites]

Those are probably amoeba or other protists, not bacteria.
posted by Blazecock Pileon at 4:11 PM on September 7, 2010

Those are probably amoeba or other protists, not bacteria

I'm thinking Paramecium. Long time ago I used to be a biologist working for a Sewage treatment plant in Norfolk, and my favorite part of the job was looking at the content of the treatment tanks to make sure it had a healthy amount of microorganisms. The medium oval blobs move like Paramecia trying to swallow bacteria. Beware the giant lurking blob at the right top edge: it looks hungry!
posted by francesca too at 4:51 PM on September 7, 2010

close encounters with protists
posted by longsleeves at 9:07 PM on September 7, 2010 [1 favorite]

Can I do with the red laser pointers around the house?
posted by LarryC at 10:35 PM on September 7, 2010

OK, what kind of laser do I need to do this? Is it something I can buy in the grocery store or do I need to go to Land o' Lasers and ask for a specific kind of laser?
posted by pracowity at 12:15 AM on September 8, 2010

I just tried this with my 50mW laser. Worked a treat.
I used gylcerin mixed with water so the droplets were thick enough that it was easy to hold on on my finger tip while lining up the beam.

Since we seem to have a lot a laser owners, my favourite trick is this:

light up a cigar and smoke it for a bit (or cigarette if you must),
turn on your laser and flick it back and forth over a 45 degree arc as quickly as you can, so you are seeing a sort of triangular "segment" of laser light.

Then, exhale your smoke over the light, you'll see an amazing cross-section of the smoke particles travelling through the beam. Works best on nights with just a little bit of moisture in the air.
posted by Dillonlikescookies at 3:12 AM on September 8, 2010 [1 favorite]

sorry i meant 5mW not 50mW, though it would probably be a lot more impressive. Standard handheld laser worked fine.
posted by Dillonlikescookies at 3:16 AM on September 8, 2010

So something like this would work?
posted by pracowity at 4:02 AM on September 8, 2010

Dillonlikescookies, now imagine how that'd look with six lasers mounted in a spinning apparatus aimed across a smoking campfire surrounded by hippies.
posted by MrMoonPie at 7:25 AM on September 8, 2010

The hippies would look radiant!
posted by Catfry at 7:37 AM on September 8, 2010 [1 favorite]

You can do this with any laser. A $1.00 laser pointer will work fine, and is the functional equivalent of the $300 tube laser I used to use in the early 90s - if not better. A sheet of blank copy paper works great as a small, bright screen, or any light colored wall in a darkened room.

I'm not sure if it would work at all with a non-coherent (non-laser) light source. Part of the effect seems to be caused by interference fringes - the distorted laser light interfering with itself with constructive and destructive interference just like in the double-slit experiment, except with thousands of moving objects suspended in a Brownian motion instead of a simple pair of slits.

I would not recommend doing this with any laser that was more powerful than 5mw, which is the cutoff point for a class IIIa consumer laser emitter. Unless you know what you're doing, and it used to be if you could afford a laser greater than 10mw you probably know what you're doing - but since people can now buy class IIIb and IIIc lasers for cheap on the internet I'm not sure if that's true anymore.

Seriously, even small lasers can screw up your eyes. I have a couple of small blind spots from low power lasers from accidentally catching the beamline and never using filter goggles.
posted by loquacious at 10:24 AM on September 8, 2010 [1 favorite]

So something like this would work?

Woah, you can get green lasers for 5 bucks now? Want.
posted by loquacious at 10:43 AM on September 8, 2010

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