Comment on "Widely tunable terahertz gas lasers"

Chevalier et al. (Science, 15 November 2019, p. 856-860) report mathematical formulas and a table predicting the threshold and the output power of terahertz molecular lasers based on various molecules. We show that these formulas are not coherent with the simple model used to describe this kind of laser, and that they largely overestimate the conversion efficiency. We suggest an alternative calculation.