This is a simple build of a Michelson Interferometer using the SpyNet Laser Tripwire . About a year ago, I accidentally came across this toy and noticed that it has a red laser and two adjustable mirrors. It also has a receiver that will sound an alarm when the laser beam that shines on it is blocked. Yes, I have reverse engineered the receiver—a rather simple circuit, really—and, of course, improved it and may post an article about it to demonstrate an SCR (Silicon-Controlled Rectifier). I requested a reviewer’s sample from Jakks Pacific but did not receive one, so I had to wait for an after Christmas sale and found a set for 80% off (about $5.00 USD which was less than purchasing a laser pointer and two makeup mirrors). Remember, do not shine the laser beam into your eyes, nor anyone else's.

Parts needs from the Laser Tripwire set:


2 Adjustable mirrors

Additional Parts:

CD clamshell

Cardboard backing from a 8 ½ X 11 notepad

Sheet of blank white printer paper 8 ½ X 11

4 Paperclips

Large binder clip

A magnifying lens (mine came from my telescope)

Something to prop the lens on (I used my copy of The Complete Works of Shakespeare)

Here’s the layout of the interferometer:

If you don’t have the Spynet Laser Tripwire set you can replace the parts with a cat toy (laser pointer) and two makeup mirrors. Here’s an excellent video by Celtic Mad Scientist that demonstrates how to build the interferometer:

I have yet to build a receiver (out of what else? Snap Circuits!), but the laser interferometer can be used for quite a number of physics demonstrations from wave/particle duality to (and don’t hold me to this because it has proved to be quite a challenge) a P-wave detector, or earthquake early warning device.