Ultra-high precision mid-IR spectrometer I: Design and analysis of an optical fiber pumped difference-frequency generation source

We report the results of a systematic characterization of various optical fiber pumping schemes for difference-frequency sources employing periodically poled LiNbO₃. Theoretical and practical considerations to achieve performance improvements for ultra-sensitive trace gas detection applications are discussed. As a result, we report a new mechanically robust and miniaturized mixing module employing a hybrid fiber with a plano-convex lens, reducing the size of previous DFG configurations by 65%. We also show pump, signal, and idler beam cross-sections before and after passing through a 100-m effective pathlength astigmatic Herriott multi-pass cell. PACS 42.55Wd; 42.60By; 42.60Jf; 42.62.Fi; 42.79.Nv