Lasers

Key Concepts

The word "LASER" stands for Light Amplification by Stimulated Emission of Radiation. A laser is an optical light source that emits a concentrated beam of photons. Lasers are usually monochromatic - the light that shoots out is usually one wavelength and color, and is in a narrow beam.

By contrast, light from a regular incandescent light bulb covers the entire spectrum as well as scatters all over the room. (Which is good, because could you light up a room with a narrow beam of light?)

Experiment & Video

Plastic Bottle Beam Fill up a plastic water or clean soda bottle with water and add a sprinkle of cornstarch. Turn down the lights and turn up the laser, aiming the beam through the bottle. Do you see the original beam in the bottle? Can you find the reflection beam and the pass-through beam?

CD Diffraction - Shine your beam over the surface of an old CD or DVD. Does it work better with a scratched or smoother surface? You should see between 5-13 reflections off the surface of the CD, depending on where you shine it and how good your "seeing" conditions are.

What's Going On?

In 1917, Einstein figured out the basic principles for the LASER and MASER (a MASER is a laser beam with wavelengths in the microwave part of the spectrum) by building on Max Planck's work on light. It wasn't until 1960, though when the first laser actually emitted light at Hughes Research Lab.

Today, there are several different kinds of lasers, including gas lasers, chemical lasers, semiconductor lasers, and solid state lasers. One of the most powerful lasers ever conceived are gamma ray lasers (which can replace hundreds of lasers with only one) and the space-based x-ray lasers (which use the energy from a nuclear explosion) – neither of these have been built yet!

Gas lasers pump different types of gases to get different laser colors such as the red HeNe (Helium-Neon laser), the high-powered CO 2 lasers that they can melt through metal, the blue-green argon-ion, the UV lasers that use nitrogen, and the metallic-gas combination such as He-Ag lasers (helium and silver) and Ne-Cu (neon and copper) which emit a deep violet beam.

But what about lasers used everyday? The lasers we're going to be using are semiconductor lasers that use a small laser diode to emit a beam. They are the same lasers that are in the grocery store scanners, pen laser pointers and key chain lasers. Usually a class I or II laser, these pose minimal safety risk and are safe to use in our experiments.  

A very neat addition to the experiments below is a fog machine. (Rent one from your local party supply store.) Turn it on, be sure you have good ventilation, darken the lights, and turn on the lasers for an outstanding laser experience! Or you can simply steam up the bathroom with a hot shower and shine your laser around (don't get the laser itself wet!).

A quick note about lasers: keychain lasers from the dollar store work just fine with these projects. Do not use the green lasers sold in astronomy stores - they are too dangerous for indoor use and cause permanent eye damage.

Keep experimenting on your own. One last thing - I really want to know how I can help my readers the most.  I want to know what your top science and education questions are... if you could sit down and have lunch with me, what are the top two questions you would ask me?  Hit your reply button now and send them to me... I guarantee that I will read them, and I will try to answer them in a future issue of the Rocket Scientist Newsletter.   

Talk soon,

Aurora