Laser pens have become so inexpensive it is easy to forget that they are small wonders of technology. If you have a laser pen you can perform some simple but striking science experiments. Have some educational fun with the kids, or just revive your sense of scientific wonder by tinkering around with lasers.
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See the Laser
Make the laser visible by creating some fog. Because lasers are made of coherent light the beam will travel straight ahead without spreading or scattering. Unlike lasers in the movies, real lasers cannot be seen except when they are being reflected by something.
To make a laser beam visible, you can use a fog machine, such as the kind you can find for parties. A bit of dry ice dropped in hot water will create a spooky-looking fog with a mad scientist vibe, too, but use it in a well-ventilated area. For a low-tech and low-budget solution, you can just beat two very dusty blackboard erasers together.
Reflect the Laser
Line up two mirrors parallel to each other, and shine the laser beam between them. By adjusting the angle of incidence carefully you can "trap" the beam between both mirrors making it bounce from one to the other in an intricate accordion pattern. (The angle of incidence is the angle at which the laser touches the surface of the mirror. You can use a protractor to measure it and see that it is equal to the angle of reflection.)
Split the Laser
Shine the beam of your laser pen into a microscope slide set at 45 degrees to the beam. When a laser meets a transparent but reflective surface a part of the beam will get through, but another part will be reflected. Repeat the procedure and create an arrangement of mirrors and slides to create complex paths for the beams to follow.
Diffract the Laser
Create patterns by shining the laser through a fine mesh or a bird's feather and onto a white wall. A laser beam can be described as an array of almost perfectly synchronised waves, and when you use a fine mesh to split the beams you interfere with that synchronisation. As a result, some waves will reinforce each other and some will neutralise each other, creating mesmerising geometrical patterns.
Reduce the risk of eye damage by using a red laser pointer with an output of less than 1 mw (that is, 1 milliwatt, or one hundredth of a thousandth of the power of a common light bulb).
For school projects, avoid high-power green laser pointers. They have a higher visibility, but they are more expensive and they can cause nearly instant eye damage unless you wear protective goggles.
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