Vibronic interactions in Nd:YAG resulting in nonreciprocity of absorption and stimulated emission cross sections

Abstract

In this paper we discuss the quantum efficiency of the metastable <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F_{3/2}</tex> state in Nd:YAG. We show that the vibronic interaction disrupts the equality between absorption and emission cross section ("reciprocity") upon which spectroscopic quantum efficiency measurements are based. Even if the electron-lattice coupling is weak, a phonon whose energy matches the energy difference between two electronic states can have a significant effect. Our spectroscopic measurements clearly show nonreciprocity and establish the importance of vibronics in Nd:YAG. The data are consistent with a high quantum efficiency.