Theory of optically pumped submillimeter

Theoretical models of the operating characteristics of both pulsed and continuous wave (CW) optically pumped submillimeter (SMM) lasers are reviewed in this study. The focus is on the SMM laser gain for both pressure and Doppler broadened transitions, with a detailed discussion of gain expressions derived from quantum mechanical calculations within a three-level molecular system. The work emphasizes the importance of incorporating pump and SMM laser induced transition rates, along with collision induced molecular relaxation rates, into theoretical treatments. The presented theoretical framework serves to bridge the gap between experimental observations and theoretical predictions, illustrating good agreement in numerous comparative studies. This research aims to provide insights that can lead to the design of improved SMM laser systems, which effectively convert pump laser radiation into SMM laser output. By outlining the underlying mechanisms and theoretical foundations, the findings contribute to a deeper understanding of SMM lasers, potentially enhancing their utility in various applications. The conclusions drawn from this theoretical review may also encourage further experimental investigations to validate and refine the proposed models.