Terahertz molecular water laser using quantum cascade laser pumping

Molecular lasers pumped by quantum cascade laser (QCL) open new possibilities for THz generation and its numerous applications, in particular, for high resolution molecular spectroscopy. In this article, a THz water laser pumped by a mid-infrared QCL was demonstrated using the broad tunability of the pump laser. Twenty D2O laser lines were measured under a continuous wave pumping regime, in a spectral range expending from 63 to 177 cm−1 (1.9–5.3 THz), and with an output power ranging from tens to hundreds of μW. This letter contains a description of the experimental setup used to produce the THz laser radiation and a comparison of the measured output power with a molecular gain factor used to sort out the most favorable laser lines. In addition to the measured laser transitions, a complete list of laser frequencies together with their corresponding molecular gain is given in the supplementary material, for both H2O and D2O isotopologues excited in their bending and stretching vibrational states.