http://hyperphysics.phy-astr.gsu.edu/hbase/mod5.html Full article >>> http://hyperphysics.phy-astr.gsu.edu/hbase/mod5.html http://hyperphysics.phy-astr.gsu.edu/hbase/mod5.html#c3 http://hyperphysics.phy-astr.gsu.edu/hbase/mod5.html#c3 Full article >>> stimulated emission Full article >>>