Abstract
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 D_2O 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 H_2O and D_2O isotopologues excited in their bending and stretching vibrational states.
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NSTL