Laser Microscope

Did you know that you can use a laser to see tiny paramecia in pond water? We’re going to build a simple laser microscope that will shine through a single drop of water and project shadows on a wall or ceiling for us to study.

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Here’s how it works: by shining a laser though a drop of water, we can see the shadows of objects inside the water. It’s like playing shadow puppets, only we’re using a highly concentrated laser beam instead of a flashlight.

If you’re wondering how a narrow laser beam spreads out to cover a wall, it has to do with the shape of the water droplet. Water has surface tension, which makes the water want to curl into a ball shape. But because water’s heavy, the ball stretches a little. This makes the water a tear-drop shape, which makes it act like a convex lens, which magnifies the light and spreads it out:

Here’s how to make your own laser microscope:

Materials:

• red or green laser (watch video for laser tips)
• large paperclip
• rubber band
• stack of books
• white wall
• pond water sample (or make your own from a cup of water with dead grass that’s been sitting for a week on the windowsill)

Download Student Worksheet & Exercises

Exercises

1. Does this work with other clear liquids?
2.   What kind of lens occurs if you change the amount of surface tension by using soapy water instead?
3.   Does the temperature of the water matter? What about a piece of ice?
4.  Does this work with a flashlight instead of a laser?
5.  Do lasers hurt your eyes? How?

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