CK-12-Physics-Concepts - Intermediate

http://www.ck12.org Chapter 23. The Atom

and used as laser pointers are continuous lasers. The photons emitted by the atoms are collected by placing the glass
tube containing the atoms between two parallel mirrors. One mirror reflects all the light striking it while the other
mirror allows some small percentage of the light to pass through. The light which passes out of the tube produces
the laser beam.

Laser light is highly directional because of the parallel mirrors. The laser beam is very small, typically around^12 mm
in diameter. The light ismonochromatic, coherent, and very intense. The concentrated power of laser light is used
in a variety of ways. In medicine, lasers can be used to repair the retina in an eye. Lasers can also be used in surgery
in place of a knife to cut flesh with little loss of blood (the laser cauterizes as it cuts). In industry, lasers are used to
cut steel and to weld materials together. Lasers may, in the future, be used to start nuclear fusion reactions.

Summary

• The word laser is an acronym. It stands forLightAmplification byStimulatedEmission ofRadiation.


• A continuous electric discharge like that in a neon sign can be used to put atoms in the excited state.


• The helium-neon lasers often seen in science classrooms and used as laser pointers are continuous lasers.


• The photons emitted by the atoms are collected by placing the glass tube containing the atoms between two
  parallel mirrors. One mirror reflects all the light striking it while the other mirror allows some small percentage
  of the light to pass through. The light which passes out of the tube produces the laser beam.


• The light from a laser is monochromatic, coherent, and very intense.

Practice

Questions

http://www.youtube.com/watch?v=oUEbMjtWc-A

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/64530

Follow up questions:

1. What substance was used to make the first laser?


2. What additions are needed on the ruby tube to get a narrow beam of light?


3. What medical procedure using lasers is mentioned in the video?

Review

Questions

1. A laboratory laser has a power of only 0.0008 watts. Such a laser seems more powerful to us than a regular
   100 watt light bulb. Suggest a reason for this.


2. A device like a laser, that emits microwave radiation is called amaser. What words are likely to make up this
   acronym?


3. What do you call an atom whose electrons have reached a higher energy state?


4. When an electron moves from a higher energy level to a lower energy level, what is emitted by the atom?