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In a past Saturday Science, we learned how to use a drop of water as a magnifying glass. Today we’re going to kick that up a few notches and use a drop of water and a laser pointer to make a working laser microscope. You’ll be able to see single-celled organisms moving around inside the laser beam!
Materials
- Pond water
- A laser pointer (you can often find inexpensive ones for $3-$5 near the check-out at the store)
- A paperclip or copper wire
- A binder clip large enough to fit around the laser pointer
- Scotch tape
- A white surface
Process
- Straighten out the paperclip, then wrap most of it around the front part of the laser pointer, leaving about an inch sticking out in front of the hole where the beam comes out. If you’re using copper wire, give yourself 3-4 inches so you have plenty to wrap around the laser.
- Secure the paperclip/wire to the laser pointer with tape.
- Carefully bend that leftover inch of paperclip/wire into a small circle, a little bigger than the laser pointer’s lens hole. Make sure it is centered right in front of the hole so the laser beam passes through it. This will hold your water drop.
- Clip the binder clip around the laser pointer closer to the front. Keep the two “arms” on the clip where they need to be to open/close it because they are the stand you will use to make sure your microscope holds steady.
- Dip your loop of paperclip/wire into your pond water. Carefully remove it, making sure there is a crop of water suspended inside the loop. If you’re having trouble getting the water droplet to stay inside the loop, make sure the loop is complete all the way around and the paperclip/wire is touching itself, forming a full circle. If there is space between one end of the loop and the other the water will have a hard time forming a stable drop.
- Carefully set your laser pointer down, using the binder clip as a stand, and point it at your white surface. Turn off all the lights in the room.
- Press the button to shine the laser beam through the water drop. It will show up on your white surface much bigger than normal and you’ll be able to see things moving around inside it. Experiment with distance: move the laser pointer closer to or further from the white surface to see what it takes to get the best focus and the sharpest image.
Summary
What are those things moving around in your laser beam?
Well, some of it is just the movement of the water. But the small dots and blobs are microorganisms that live in the pond water, like paramecia and amoeba. These single-celled organisms swim around the water using tiny hair-like structures called cilia or flagella. There may even be some single-celled plant-like lifeforms called diatoms. Your laser microscope isn’t powerful enough to make out fine details in these microorganisms, but how cool is it that you can see them moving around in the beam of a laser?
This works because the water drop is similar in shape to the lens of a real microscope. A lens takes the light waves moving through it and bends them so they start traveling outward as they leave the water drop. The laser beam continues expanding until it hits the white surface. The microorganisms swimming around in the pond water get in the way of the light, which means they cast shadows inside the laser beam. Those shadows are what you see moving around in the light.
Want more Saturday Science? See all of our at-home activities on the blog or on Pinterest.
