Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 30 - Think and Explain - Page 579-581: 65


A situation known as population inversion is necessary for a laser to operate.

Work Step by Step

A population inversion is a situation in which more atoms are in higher, excited states than in lower, unexcited energy states. This is not the normal situation, and thus is called an "inversion". The excited, metastable helium state should be relatively long-lived, so there are enough excited helium atoms to achieve population inversion. If they state de-excited too quickly, there wouldn't be enough excited helium atoms to efficiently transfer energy to neon atoms, creating a population inversion in the neon atoms too.
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