Chemistry in lasers. IX. A re-examination of the Einstein coefficients and two level population inversion

From a re-examination of the Einstein coefficients in terms of current theory the common assumption that population inversion cannot be maintained in a two level system by optical pumping is shown to be erroneous. The nonisotropy of the radiative ensemble in an optical resonant cavity, absent from the original derivation by Einstein, is shown to be of decisive importance. (auth)