Creating a Laser Could we just bounce one clump back and forth in one direction so that it built up really big? Yes, that's exactly what we do...we use mirrors to bounce the photons back and forth along one direction through the atoms. In this next applet we add mirrors to the energy pump that gives the population inversion and we have built a laser! This applet lets you picture the laser light as either particles or waves, but it's really two different ways of thinking of the same thing. If you're curious why the wave inside the laser doesn't seem to move either left or right, come read about Standing Waves Cool! If the energy pump is high enough, eventually it builds up into a bigger and bigger wave or clump of photons. Wait...we have a leak. Some of the light is escaping to the right. That is so we can get the beam of laser light out! A laser would not be very useful if all the light was always held inside. We use a partially reflective mirror on one end so that some of the light leaks through. Wow...so the beam inside the laser is a lot more powerful than the beam that actually comes out. Also notice how we can't get the device to "lase" (yes, it's a verb, too...) unless enough atoms are excited. That's the "population inversion" we talked about before. When I push the button on a laser pointer it works right away. Why does it take so long for anything to happen in this laser? With real atoms and real lasers everything happens very fast. To make it easier for you to see, everything in this laser section is running a billion times slower than it does with real atoms and real light! In a real laser the atoms are also about a billion times smaller and there are a billion times more of them.

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