Lasers Experiments & Videos

Most people know not to shine lasers into sensitive places like eyeballs, but very few people can tell one laser from another. The truth is that not ALL lasers are dangerous, and there are different classifications of lasers. The most important information you need about laser safety is printed right on the laser itself.

Basic Laser Guidelines for Safety:
1. Never look directly at the beam source, or aperture
2. Never point the beam at another person
3. Always be mindful of where a “bouncing beam” will land due to reflection

Laser light is collimated, meaning that it travels in parallel rays. Here’s a really cool experiment that will show you the difference between a non-collimated light, like from a flashlight and collimated light from a laser.

Ordinary light from a light bulb diverges as it travels. It spreads out and covers a larger and larger area the further out you go. A laser has little to no divergence, so we way that laser light is collimated.

Lasers light is different from light from a flashlight in a couple of different ways. Laser light is monochromatic, meaning that it’s only one color.

Laser light is also coherent, which means that the light is all in synch with each other, like soldiers marching in step together. Since laser light is coherent, which means that all the light waves peaks and valleys line up. The dark areas are destructive interference, where the waves cancel each other out. The areas of brightness are constructive interference, where the light adds, or amplifies together. LED light is not coherent because the light waves are not in phase.

The angle that the reflected light makes with a line perpendicular to to the mirror is always equal to the angle of the incident ray for a plane (2-dimensional) surface.

We’re going to play with how light reflects off surfaces. At what angle does the light get reflected? This experiment will show you how to measure it.

This simple activity has surprising results! We’re going to bend light using plain water. Light bends when it travels from one medium to another, like going from air to a window, or from a window to water. Each time it travels to a new medium, it bends, or refracts. When light refracts, it changes speed and wavelength, which means it also changes direction.

If you’re scratching your head during math class, wondering what you’ll ever use this stuff for, here’s a cool experiment that shows you how scientists use math to figure out the optical density of objects, called the “index of refraction”.

How much light bends as it goes through one medium to another depends on the index of refraction (refractive index) of the substances. There are lots of examples of devices that use the index of refraction, including fiber optics. Fiber optic cables are made out of a transparent material that has a higher index of refraction than the material around it (like air), so the waves stay trapped inside the cable and travel along it, bouncing internally along its length.  Eyeglasses use lenses that bend and distort the light to make images appear closer than they really are.
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Gummy bears are a great way to bust one of the common misconceptions about light reflection. The misconception is this: most students think that color is a property of matter, for example if I place shiny red apple of a sheet of paper in the sun, you’ll see a red glow on the paper around the apple.

Where did the red light come from? Did the apple add color to the otherwise clear sunlight? No. That’s the problem. Well, actually that’s the idea that leads to big problems later on down the road. So let’s get this idea straightened out.

Diffraction is how light bends as it passes through very narrow slits or around very thin objects like a hair. When light travels around a hair, two wave patterns form, and those waves interfere with each other constructively (they add together to form a bright region) or destructively (the cancel each other out and leave a dark spot).

This experiment looks at the light and dark areas of interference to determine the wavelength of a laser. You can do this for lasers that don’t have labels on them, so you really don’t know what wavelength they are!

We’re going to use a laser pointer and a protractor to measure the microscopic spacing of the data tracks on a DVD and a CD. The really cool part is that you’re going to use an interference pattern to measure the spacing of the tracks, something that you can’t normally see with your eyes.

Interference is what happens when waves smack into each other. When the waves collide, if the two highest or two lowest points of the waves are lined up, then they add together to form a larger amplitude which is seen as a bright spot of light. However, if a peak and a trough line up, then they cancel each other out and there is a dark area in the pattern (see the dark spaces in the line?).