Modeling mid-infrared fiber laser systems

Mid-IR fiber lasers are complex nonlinear dynamical systems, involving interplay between many physical phenomena and offering vast design freedom. The development of numerical models to simulate laser behavior is, therefore, an invaluable tool, both to optimize output performance and to advance understanding of novel laser transitions. Such insight would be significantly slower and more costly to obtain (or indeed, impossible) through laboratory experimentation alone. In this chapter, we offer a general introduction to various topics in mid-IR fiber laser modeling, with a particular emphasis on rate equation simulations. Complete formalisms are developed from first principles, notably using a matrix approach, which is well suited for complex mid-IR transitions, and we discuss practical solution strategies. Case studies are presented for CW, Q-switched, and gain-switched lasers, considering both the dysprosium and the erbium ion. The second part of the chapter then considers thermal modeling to identify cooling strategies for high-power systems and ultrashort pulse simulations for modeling mode-locked lasers.