Chapter 15

1. Chapter 15 Section 3 Lasers

2. Objectives • Describe the properties of laser light. • Explain how laser light has particular advantages in certain applications.

3. Lasers • Have you ever asked yourself, how certain things work?  For instance, how can police officers measure how fast you are going in your car or how does your CD player works?  What about the movement of the earth’s crust and the measurement of earthquakes?  Well it just so happens that all of these questions can be found out using lasers.  So what is a laser?  How do they work?  What are they used for?  Lasers are studied in physics and help us understand many things. •             If you asked a person 50 years ago, what a laser was, he or she would have a very confused look on their face.  If you asked a person today what a laser was they would give you answer, but probably wouldn’t be able to tell you how they work.  A laser is a device that control the way excited atoms release photons or particles of light (Weschler).  The word laser is not only a word, but an acronym.  It stands for Light Amplification by the Stimulated Emission of Radiation.   Once you understand what the different letters mean in this acronym, you will understand how a laser works (Jezek).

4. Lasers • A laseris a device that produces coherent light at a single wavelength. • The word laser is an acronym of “light amplification by stimulated emission of radiation.” • Lasers transform other forms of energy into coherent light. • The light produce by a laser has unique properties that make it very useful for many applications

5. Applications of lasers • Lasers are used to measure distances with great precision. • Compact disc and DVD players use lasers to read digital data on these discs. • Lasers have many applications in medicine. • Eye surgery • Tumor removal • Scar removal

6. Properties of lasers • Three Unique Properties: •     Lasers are very different from normal, everyday light.  There are three properties that every laser has that make them unique from normal light.  Laser light is monochromatic which means it has one specific wavelength of light or one color of light.  The color of light is determined by the amount of released energy when an electron goes from an excited state back to ground state.  The laser light released is also coherent.  This means that the photons move in an organized fashion with other photons.  They all have the same wave fronts.  Lastly, laser light is extremely directional.  Unlike normal light that spreads out in many directions, lasers are concentrated and light is only projected wherever the laser is pointing to (Weschler).     • Uses of Lasers: • The uses of lasers are endless.  Lasers are used in geology, medicine, optometry, supermarkets, optical networks, mechanics, construction, lab experiments, and many more.  The devices used when lasers first were developed were very primitive, but today lasers have revolutionized many areas of science and have been a big success in these areas. • Laser beams have been bounced off reflectors on the moon which would provide information of the movement of Earth’s crust (Background).  In the field of medicine, lasers are used to remove scarring or tattoos from a person’s skin, seal off bleeding blood vessels, kill cancerous cells, and also can get rid of small growths in places inaccessible on the body such as the bowel and vocal cords (Lasers Revolutionize).

7. Properties of lasers • Optometrists use lasers to correct a person’s vision and to attach retinas back into place without making a cut.  Lasik, which stands for Laser-Assisted In Situ Keratomileusis, Eye Surgery uses an excimer laser to permanently change the shape of the cornea in your eye that will in turn reduce the dependency on glasses and contact lenses.  Optometrists also use a procedure called a PRK, Photorefractive Keratectomy, with lasers to correct myopia, hyperopia, and astigmatism (Lasik).

8. Laser classification • Lasers are classified in five groups according to the medium used to create the laser light.  Lasers can be solid state, semiconductor, dye, gas, or excimer lasers.  Each group of lasers has certain attributes that a laser must have to be classified in that group.  Solid state lasers use a solid laser-creating medium and an example of a solid state laser is a ruby laser, which uses a tube of ruby to create the laser light.  Semiconductor lasers or sometimes called diode lasers are usually very small and use a small amount of power.  They are very weak and can be found in laser pointers and in optical networks such as fiber optics.  Diode lasers emit a red beam of light that has a wavelength between 630 nm and 680-nm.   •     Dye lasers use organic dyes as mediums to create laser light.  The dye is mixed or suspended in a liquid.  Dye lasers can create various wavelengths of light.  Gas lasers, as you might guess, use gases for mediums to create laser light.  The most common gas lasers are helium and helium-neon lasers which are found in grocery store checkout lines.  Gas lasers also could be made to cut through hard substances.  Lasers that use carbon dioxide as a medium can cut through objects such as steel.  To cut through a hard substance, the gas laser “cuts” through it by melting whatever it is pointing at.  The final groups of lasers are the excimer lasers.  These lasers use reactive gases mixed with non-reactive gases to create its medium.  When this laser is stimulated by electricity, a molecule develops that gives off ultraviolet light.  Thus the light that an excimer laser gives off is ultraviolet light (Lasers).

9. Video • Let’s watch a video on lasers • Properties of lasers • Exploring lasers