Positivity of entropy production for the three-level maser

Entropy production is a key concept of thermodynamics and allows one to analyze the operation engines. For Scovil-Schulz-DuBois heat engine, archetypal three-level thermal maser coupled baths, it was argued that common definition flow may provide negative entropy for certain parameters [Boukobza Tannor, Phys. Rev. Lett. 98, 240601 (2007)]. Here, we show this can be cured if corrections detuning are properly applied energies used bath transitions. This method more generally thermodynamical analysis optical transitions where modes light field detuned from transition energy.