Science Teleclass: Light & Lasers

Monday October 6, 2014
This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I've included it here so you can participate and learn, too!

This class is all about Light Waves! Energy can take one of two forms: matter and light (called electromagnetic radiation). Light is energy in the form of either a particle or a wave that can travel through space and some kinds of matter, like glass.

We're going to investigate the wild world of the photon that has baffled scientists for over a century. We'll also do experiments in shattering laser beams, bending and twisting light, and also split light waves into rainbow shadows. Materials:
  • laser pointer
  • flashlight
  • paper clip
  • gummy bear (green and red)
  • old CD
  • paper clip
  • rubber band
  • pond water (just a little bit)
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What is a Laser?

Thursday March 20, 2014

Have you ever wondered why you just can’t just shine a flashlight through a lens and call it a laser? It’s because of the way a laser generates light in the first place.

The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation.
That’s a mouthful. Let's break it down.

Let's do an experiment that shows you how a laser is different from light from a flashlight by looking at the wavelengths that make up the light.

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Laser Collimation

Thursday March 20, 2014

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.


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Laser Coherence

Thursday March 20, 2014

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.


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Measuring the Wavelength of a Laser

Thursday March 20, 2014

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!


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Gummy Bears, Absorption, and Transmittance

Thursday March 20, 2014

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.


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Lasers, Jell-O and Trigonometry

Thursday March 20, 2014

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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Reflection Law using a Laser

Thursday March 20, 2014

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.


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Refraction using Lasers and Water

Thursday March 20, 2014

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.


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Laser Safety

Thursday March 20, 2014

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


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Fluorescence

Tuesday September 3, 2013

Fluorescent minerals emit light when exposed to ultraviolet (UV) light, usually in a completely different color than when exposed to white light. UV is invisible to the human eye, and is the wavelength of light that is responsible for sunburns.


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Measure the Track Spacing of a DVD and CD

Sunday September 1, 2013

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?).


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Measure your Hair Width with a Laser

Sunday April 21, 2013

Do you have thick or thin hair? Let’s find out using a laser to measure the width of your hair and a little knowledge about diffraction properties of light. (Since were using lasers, make sure you’re not pointing a laser at anyone, any animal, or at a reflective surface.)


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Answers to ‘Lasers’ Exercises

Wednesday February 3, 2010

Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!


Here’s printer-friendly versions of the exercises and answers for you to print out: Simply click here for printable questions and answers.


1. Light can change speed The word “LASER” stands for Light Amplification by Stimulated Emission of Radiation.


2. Light from a regular incandescent light bulb covers the entire spectrum as well as scatters all over the room. A laser beam is monochromatic – the light that shoots out is usually one wavelength and color, and is in a narrow beam.


3. Glass (like a window pane) and clear plastic (like a water bottle).


4. Take it in a steamy room, like just after a hot shower. Or aim it through a glass of water that has a drop of milk in it.


5. The laser beam hits a spinning mirror that’s off-center. The more angled the mirror mount, the larger the image that the laser traces out. Which is why this is a perfect project for kids – the sloppier they build it, the better the laser light show.


6. High-power CO2 lasers have an intense amount of heat that melts through metal. These aren’t the lasers we’re going to be working with! The lasers at the grocery store are Class I lasers, which will harm your eye if you stare into it without blinking once for at least 15 minutes. These ‘keychain’ lasers are Class II & III, some of which can overpower your retina in less than a minute, and the damage is irreversible. When I work with kids in a live Laser Lab class, I have a zero-tolerance rule (which is explained beforehand): if misused, I just walk over, take the laser without a word, and keep it. Class proceeds as normal, and it’s up to the kid to figure out how to finish the project.


Laser Basics

Wednesday February 3, 2010

Did you know that the word LASER stands for Light Amplification by Stimulated Emission of Radiation? And that a MASER is a laser beam with wavelengths in the microwave part of the spectrum? Most lasers fire a monochromatic (one color) narrow, focused beam of light, but more complex lasers emit a broad range of wavelengths at the same time.


In 1917, Einstein figured out the basic principles for the LASER and MASER 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!


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Laser Maze

Wednesday February 3, 2010

By using lenses and mirrors, you can bounce, shift, reflect, shatter, and split a laser beam. Since the laser beam is so narrow and focused, you’ll be able to see several reflections before it fades away from scatter. Make sure you complete the Laser Basics experiment first before working with this experiment.


You’ll need to make your beam visible for this experiment to really work.  There are several different ways you can do this:


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Laser Light Show

Wednesday February 3, 2010

ss-laserWhat happens when you shine a laser beam onto a spinning mirror? In the Laser Maze experiment, the mirrors stayed put. What happens if you took one of those mirrors and moved it really fast?


It turns out that a slightly off-set spinning mirror will make the laser dot on the wall spin in a circle.  Or ellipse. Or oval.  And the more mirrors you add, the more spiro-graph-looking your projected laser dot gets.


Why does it work? This experiment works because of imperfections: the mirrors are mounted off-center, the motors wobble, the shafts do not spin true, and a hundred other reasons why our mechanics and optics are not dead-on straight.   And that’s exactly what we want – the wobbling mirrors and shaky motors make the pretty pictures on the wall!  If everything were absolutely perfectly aligned, all you would see is a dot.


Here’s how to do this experiment:


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Space-Age Laser Communicator

Wednesday February 3, 2010

laser17This experiment is for advanced students.Did you know that when you talk inside a house, the windows vibrate very slightly from your voice? If you stand outside the house and aim a laser beam at the window, you can pick up the vibrations in the window and actually hear the conversation inside the house.


Remember how windows split a laser beam in two from the Laser Basics experiment? That’s the basic idea behind it. First, I’ll show you how to build your own space-age laser communicator, then you can work on your spy device.


The first thing we’re going to do is take the music from your stereo or MP3 player and transmit it on a laser beam to a detector on the other side. The detector has an earphone attached, so someone else can listen to the music from your laser. Weird, huh?


Here’s how to build your own:


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Unit 9: Lasers Video

Wednesday February 3, 2010

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?).


Soon you’ll be building shattering light rays, firing music on a laser beam, and building your own laser light show from tupperware. Let’s get started by learning about lasers with this video:


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