Easy LASER Experiments

The Red Spot

Visible Laser Diodes (VLDs) and Helium Neon (HeNe) lasers both produce a brilliant red spot at great distances. You can do some very annoying things using this property, but I don't suggest you do. Do not aim the laser into other people's windows, eyes or moving automobiles. You could get into some serious trouble.

You can have some innocent fun with your own (not someone else's) dog or cat. If you let the animal rest periodically, you will do the animal no harm, while you make its life extremely interesting. A dog or cat will be very interested in the red spot if you make it behave as if it's alive. For example, move the spot across the yard, and turn it off to make it look like the spot disappeared under a rock or other object. A dog will sniff around the spot for several minutes.

A cat will chase the spot across the yard at full speed, in any direction. It's as if you suddenly have a remote control for your pet. You can actually make a (young) cat climb your curtains, but again, this may not be a wise thing to do.

Again, take it easy on your animal and you will not hurt it.

Fog Effects

Low powered VLDs and HeNe lasers do not produce visible beams in clear air, unless you look almost directly into them, at which time you see a sparkling effect produced by the beam scattering off of dust particles. Mount the laser on a tripod and aim it across a large field at night. Hike to the other end of the field and look back at the laser (while you're there, measure the diameter of the beam - you'll be surprised). To be able to see the beam from larger angles requires that the beam be scattered by more than just dust. The fog produced by professional fog machines is ideal, but if you don't have one of these, use dry ice to make fog. Just drop chunks of dry ice into some hot water for a dense ground - hugging fog. For safety, don't allow anyone - pets or people - to lay down in this fog, as they could be asphyxiated. CO₂ gas does not support animal or human life.

Fog Cutter

While you've got this dense fog filling your living room, try this; Get a small polished cylindrical object, such as a drill bit, and aim the laser beam at the cylinder. The beam will spread out into a fan. Aiming the beam through a glass or clear plastic stirring rod will do the same thing. Now orient the cylinder or rod vertically so the laser fan sweeps out in a horizontal sheet. Look at the cross section this cuts in the fog. Try not to disturb the fog too much, but let it settle down into a steady, ever shifting maelstrom of micro eddies and vortices. It's incredible to watch.

Diffraction Grating Effects

Direct the beam of your laser through those diffraction grating glasses you can buy in novelty shops, and project the pattern on a wall or ceiling. You will get a rectilinear array of laser spots. Overlap two of the diffraction gratings and rotate them slowly against each other for a very impressive molecular - grid - looking effect. You can reflect the laser beam off of diffraction foil patterns for different but similar effects.

Caustics, Refraction and Interference effects

Get together a collection of cut or molded crystal or glass objects. Butter dishes, stemware, etc. Direct the laser beam through the pieces individually and aim at the ceiling. If you scan the beam very slowly over different regions of the glass piece, you will find regions where incredible caustics are generated. They appear as warped netting, fine structured traceries of clouds or alien atmospheric phenomena. Cut crystal performs better than molded glass, because it has sharp edges. But cut crystal is much more expensive. You may want to experiment - carefully - with pieces of broken glass.

A Laser X-Ray

You can use your laser as a sort of X-ray machine, to examine the inside of a frosted lightbulb. This can be a quick way to check the filament of the bulb. Shine the laser pointer onto the light bulb, and observe it from the opposite side. You will see a clear shadow of the filament, so you can tell if the filament is broken.
How does this work? The laser pointer creates a tiny spot of light on the bulb. The frosted coating on the bulb causes this light to spread in all directions. As it crosses the inside of the lightbulb, the filament creates a shadow that appears on the frosted coating on the opposite side of the bulb. Please note that the only reason to use a laser for this is because it produces a small, very bright point of light. Theoretically, you could punch a hole in a piece of cardboard, shine a bright light through it, and hold the lightbulb against the hole while examining it from the other side. A comparison of these two methods might make a nice science fair project.