Science Alliance

LASER Pointer Activities

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LASER Pointer Safety - from Princeton University

LASER Demonstrations: Note: To Keep your LASER pointer on, without holding it, while doing your demos I recommend using a medium sized (1 1/4" wide) binder clip.

See the Light

Materials: LASER pointer (with binder clip), erasers equipped with chalk dust

Set up your LASER pointer and then clap your erasers to make the beam visible. The tiny particles help to scatter the light in many directions making the beam easily seen.

You can also shine your LASER beam into a tank of water where some substance has been dissolved to make the water a bit cloudy.

Rainbows

Materials: slide projector, screen or light colored wall, slide with slit (optional), LASER pointer (with binder clip)

Shine the white light from the slide projector through a glass prism and onto a screen or light colored wall. Play a little with the exact orientation of the prism and soon you should see a nice spectrum on the wall or screen. Using a dark slide with a slit cut out makes it easier to do. The spectrum appears because each color of light is bent differently, thus spreading them out.

Shining the LASER pointer through the prism should demonstrate how different LASER light is from white light. The LASER light is monochromatic, just one color. So you see the same color on either side of the prism.

Inteference

Materials: screen or light colored wall, LASER pointer (with binder clip), and diffraction grating

Set up your LASER pointer so that it shines through a diffraction grating. Shining on your wall or screen will be a pattern similar to what you see above. Instead of just one spot of LASER light there will be many!

Why?

Light is a wave! So when the LASER light passes through a diffraction grating, the wave will be split by the grating and re-form on the other side in a pattern of constructive and destructive interference. What is constructive and destructive interference? When waves of any kind (water, sound, light) meet they interact. One possibility is that they can wipe each other out. This is known as destructive interference and is seen as the dark areas between the bright spots. The other possibility is that they can add together. This is called constructive interference and it produces the bright spots.

Twinkle, Twinkle Little Star

Materials: hot plate, LASER pointer (with binder clip), screen or light colored wall, slide projector, slide of stars

Set up the LASER so that the beam passes over the top of the hot plate and makes a spot on the wall some distance away. Turn on your LASER and look at the spot on the wall. Then turn the hot plate to high. The spot of LASER light will start to move around much like a twinkling star. If the hot plate is turned off the spot will eventually stop moving.

By using a slide projector with a slide of stars instead of the LASER you can demonstrate the same effect. Also try a slide of the Moon. Does it twinkle? Why or why not? Also try using the slide projector without a slide! Shine the light over the hot plate and the turbulent air will become easily visible.

How is this like the real twinking stars and our atmosphere? The way light travels through air depends on the temperature of the air. The hot air rises from the hot plate deflects the light slightly due to the turbulence of the air above the heat source. In the real atmosphere when you look at a twinkling star its light passes through Earth's turbulent atmosphere. The temperature changes are smaller, but the light shines through a much longer path!

Why don't planets twinkle? Planets (or the Moon) look larger than stars, and the effect is less noticeable because they occupy a larger part of the sky.