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Gaseous ammonia has previously been demonstrated as a compelling gain mediumfor a quantum cascade laser pumped molecular laser (QPML), exhibiting goodpower efficiency but limited tunability. Here we explore the potential of theammonia QPML to produce powerful, broadly tunable terahertz frequency lasing onrotational and pure inversion transitions. After theoretically predictingpossible laser frequencies, pump thresholds, and efficiencies, weexperimentally demonstrate unprecedented tunability -- from 0.762 to more than4.5 THz -- by pumping Q- and R-branch infrared transitions with widely tunablequantum cascade lasers. We additionally demonstrate two types of multi-linelasing: simultaneous pure inversion and rotation-inversion transitions from thesame pumped rotational state, and cascaded lasing involving transitions belowthe pumped rotational state. We report single frequency power levels as greatas 0.33 mW from a low volume laser cavity.

Multi-line lasing in the broadly tunable ammonia quantum cascade laser pumped molecular laser