Four level laser

In the four level laser system, the atoms from ground state E1 are raised to excited state E4 with the help of pumping. From the E4, the atoms decay to energy state E3 by spontaneous emission. The transition rate of atoms from E4 to E3 is much faster as compared to transition rate of atoms from E3 to E2. This is due to the reason that E4 is an excited state with life time of the atoms of the order of 10-8 seconds.

E3 is the metastable state. Thus the number of atoms in E3 exceeds the number of atoms in E2. The population inversion is achieved between E3 and E2. The laser action takes place between E3 and E2 by stimulated emission. The atoms from energy state E2 get deexcited to E1. The atoms from E1 are again pumped to E4.

Example: Helium-Neon laser is four level laser system.

Advantage of four level laser:

The rate of relaxation of the atoms from E2 to E1 should be faster than the rate of arrival of atoms from E4 or E2.

This is required for better efficiency of laser system. Thus, four level laser is better than three level laser.

Reference: This article is referred from my authored book “optics and lasers” having ISBN 81-272-2948-2. In case of any doubt, post in the comment section.

Kindly Read This Also :

Note from winnerscience: If you want the e-notes of all the laser  articles that will include the basics of lasers like stimulated absorption, difference between spontaneous and stimulated emission, Einstein  Coefficients, properties and applications of lasers, complete construction and working of lasers like Ruby laser, He-Ne laser, Carbon dioxide laser, Nd:YAG laser, dye laser, semiconductor laser, holography and additional articles of Q-switching and mode locking, then please contact [email protected]. You can post your queries also there.

6 Replies to “Four level laser”

  1. I think there is a young error in the end of four level Laser. The atoms from E1 are again pumped to E2? Shouldn’t it be “The atoms from E1 are again pumped to E4” ?

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.