5 Tricks You Did Not Know You Could Do With Lasers


Adam Beehler

In each newsletter, Adam Beehler, Lecture Demonstration Specialist, explains one of his demonstrations.

I was contemplating some of the cool things that could be done by folks with common, everyday materials. It was not long before I remembered the laser. What was non-existent in the not too distant past, is now ubiquitous & necessary for so many other applications. To many people, a laser is considered just a toy. So, here are a few activities that I have enjoyed over the years that are made possible, or easier, with a simple laser pointer, found at any office supply store.

 

1) Laser Spirograph

(Lissajous Patterns*)

I think I first saw such an arrangement at the Little Shop of Physics outreach program at Colorado State University. Taking a laser pointer and aiming it at a mirror, the beam is directed toward a second mirror, and then on to a third mirror. Each mirror is mounted onto a little motor that can be controlled by a switch (both items easily found at any hobby supply store). In this way, one rotating mirror can reflect the beam in one direction while another mirror can reflect that same beam in another direction. Due to the persistence of vision of our eyes, we see the beam drawn around in wonderful patterns on a screen. I have personally made a little portable version with the components mounted on a board. It was a big hit one campout when I projected cool, moving patterns onto the trees at night.

2) Laser Waterfall

(Total Internal Reflection)

This can be done as simply as filling a plastic bottle with water, and then poking a small hole near the bottom of the bottle to allow a stream of water to smoothly shoot out and down. Now all that is required is to aim the laser beam through the water-filled bottle and into the water stream. A fair amount of the light will totally internally reflect inside the water stream and be guided down with the stream. Placing one’s hand into the stream should reveal the laser light shining on your skin, and mixing in a little scattering agent (such as Pine-Sol or milk) can make the beam more visible.

3) Change Color

(Fluorescence - Cool Color Changes)

We are able to send laser beams through different materials and see the path of the beam due to the scattering of the beam off of microscopic particles within the material through which it passes. This is cool in and of itself. We can literally show reflection, refraction, dispersion, and total internal reflection. However, by choosing different materials to shine the laser through, we can also affect the color of the beam. Some of the light may be absorbed by the medium and excite the dye above its ground energy state. If this transition is followed by another instantaneous transition back down to some excited state above the ground energy state, then it radiates lower energy photons than those used to excite it in the first place. This is known as fluorescence. It is a common misconception that fluorescence only occurs when using ultraviolet light (UV), yet that is wrong. I enjoy taking my green laser pointer (as well as my UV laser pointer) and shining it through anything I can think of in my house.

4) Transition Lenses

(Photochromism)

Materials that change their color upon illumination are called photochromic materials, and the phenomenon is known as photochromism. The material’s molecules are transparent to visible light in the absence of UV light, but when exposed to UV light, the molecules undergo a chemical process that causes them to change shape. The new molecular structure absorbs portions of the visible light, causing the lenses to darken. Upon removing the UV light, a different chemical reaction takes place, and the molecules go back to their original shape. A simple way to see this effect is to get some photochromic sunglasses and go outside into the sun, but it is more fun to try it with a UV laser pointer. Don’t worry, the lenses will go back to normal.

5) Laser Radio

(Beam Modulation)

Using a simple laser pointer, a few miscellaneous parts*, and a bit of time, one can make a simple laser communicator. It converts a sound source into light that travels across a room and then back into sound with very little quality loss. Basically, the laser light is amplitude modulated. This simply means that the amount of light the laser emits varies over time. A solar cell can pick up the signal and convert it back into sound. I have piggy-backed music on a laser beam down a long hallway successfully

You can also view this demo, and a complete materials list, here.