How is LASER light different from white light? Teacher Notes

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1 How is LASER light different from white light? Teacher Notes Concepts: (1) Light is a type of energy that travels as waves. [ ] (2) Laser light is different from traditional light sources and must be used with care. [ ] (3) Different kinds of light can do work for us. Questions to get students thinking before the activity or to use after: What is laser light? What can lasers be used for? How do lasers solve problems for us? How is laser light different from the light in the classroom? Materials per group: red low wattage LASER pointer with LED flashlight white light (strong flashlight not LED) diffraction grating (available online or from science supply catalogues) SAFETY NOTE: avoid rainbow glasses, you do not want the kids to use them to look at the laser light. white paper (walls work too) tape Procedure: Review laser safety before doing this activity. Make sure you try this one ahead of time. The best light source to use for procedure 4 is an incandescent light bulb. AVOID DIRECT EXPOSURE TO BEAM CLASS IIIa LASER PRODUCT If you cannot get rainbows with a flashlight you can look at the room lights through diffraction grating. Just make sure the laser pointers are set aside! Observations/Results: A strong white light shown through a diffraction grating will produce a rainbow. (White light is made of all the colors. When we see all the colors of light reflected to us, we interpret that as white.) Only red light is seen when the laser light goes through the grating. The laser light is seen across the room and the white light is not. The laser light is focused into a small spot and the white light is not. Summing Up: 1.Is LASER light the same as normal white light? Describe two ways they are different. Laser light makes a small spot, white light spreads out. Laser light travels much further than white light. Laser light is only one color (red) but white light is really all the colors.

2 2.If you had to send a light from Earth to the moon, would you use white light or LASER light? Why? Laser light because it travels much further without spreading out than white light does! Have your students read What is LASER light? after doing this activity. Questions: 1.What does LASER stand for? LASER stands for Light Amplification by Stimulated Emission of Radiation 2.Laser light is monochromatic. What does that mean? It means only one color. 3.Draw a wave. Indicate the location of a crest and a trough. Use an arrow to show the length of a wavelength. wavelength crest trough 4.Lasers come in all different colors. Some lasers send out wavelengths of light the eye cannot see. Each color of light has a different wavelength. The wavelengths of visible light are very small. The label on a laser says the wavelength of the light 532nm. Use the diagram below to tell what color of light is emitted by the laser. It would be green. 5.Can laser light be found in nature? No. 6.List three properties of LASER light that white light does not have. Laser light is monochromatic (one color), coherent (all the crests are lined up or amplified) and it is coherent (the light does not spread out).

3 How is LASER light different from white light? Purpose: The purpose of this activity is to learn what a LASER is. Materials: red low wattage LASER pointer with LED flashlight, white light (strong flashlight not LED), diffraction grating, white paper, tape SAFETY NOTE: Never look directly at LASER light! Follow the directions carefully. Procedure: 1.Read the LASER safety rules. Make sure every member of the group understands and agrees to follow the rules. AVOID DIRECT EXPOSURE TO BEAM CLASS IIIa LASER PRODUCT 2.Tape a piece of white paper to the wall about waist high. 3.From about 2 feet away, shine the white light from the pointer and then the LASER light at the paper. Compare the spots of light from the two sources. 4.a)Shine the white light of a strong flashlight through the diffraction grating onto the white paper. You may need to adjust the position of the light and diffraction grating until you see an image. How many colors do you see? b)carefully shine the LASER pointer through the diffraction grating at the white paper. How many colors do you see? 5.CAUTION: make sure you warn your classmates before you do this step! Turn and face the other side of the room Turn on the pointer s flashlight. Standing in the same place, turn on the pointer s LASER. Compare how much light from each source gets to the other side of the room. Summing Up: 1.Is LASER light the same as normal white light? Describe two ways they are different. 2.If you had to send a light from Earth to the moon, would you use white light or LASER light? Why?

4 What is LASER light? LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. Laser light is different from normal white light in many ways. First of all, laser light does not exist in nature; laser light is man made! Let s take a quick look at how laser light is produced. Inside a laser there is a crystal such as a ruby. Within the crystal the electrons are excited so more of them have higher energy than have lower energy. Both ends of the containment tube are covered with reflective surfaces. This permits photons (particles of light energy) to reflect back and forth, building up in each passage. The photons bounce back and forth between two mirrors until coherent light escapes from the cavity. The activity showed you three ways laser light is 1 different from normal, white light. When white light is put through a diffraction grating or prism it separates into many colors. White light is made up of all the colors of the rainbow. Laser light is different. clipartpanda.com When you passed the laser light through the diffraction grating it produced only red light. Laser light is monochromatic. The light from the laser pointer contained only the red wavelengths of light. As shown in the picture to the left, the wavelength is the distance between the high points (crests) wavelength of a wave. Green light has a shorter wavelength than red light does. The wavelength of the laser light from the pointer should be printed on the label. Laser light is coherent light. All the crests are lined up, the light is amplified. This allows laser light to travel great distances. You saw this when the laser light made it all the way across the classroom and the white light did not. Yet another way that laser light is different it that laser light is collimated. All the waves are traveling in the same direction. That means a narrow, concentrated spot of light is seen on a surface. The flashlight did not produce a concentrated spot of light - the light was spread out or diffuse. Because laser light travels great distances and in straight lines without spreading out, they can be used in levels and for surveying. Lasers are used in bar code scanners, CD players and game systems. Stronger lasers are used to cut metals. Lasers can even be used to cut tissue during surgery. Questions: 1.What does LASER stand for? 1 has an excellent demonstration of the differences between laser light and normal light.

5 ! 2.Laser light is monochromatic. What does that mean? 3.Draw a wave. Indicate the location of a crest and a trough. Use an arrow to show the length of a wavelength. 4.Lasers come in all different colors. Some lasers send out wavelengths of light the eye cannot see. Each color of light has a different wavelength. The wavelengths of visible light are very small. The label on a laser says the wavelength of the light 532nm. Use the diagram below to tell what color of light is emitted by the laser. red orange yellow green blue purple 700nm 600nm 500nm 400nm 5.Can laser light be found in nature? 6.List three properties of LASER light that white light does not have.