In optical pumping, less can be more


Lasing is based on the process of optical gain. Once this gain provided through external pumping surpasses the loss in a resonator, lasing sets in and a coherent beam of laser light is emitted. Thus, loss is a natural adversary of lasing, at least in common lasers. A striking amendment to this rule is reported on page 328 of this issue by Peng et al. (1), who report an onset of lasing in a pair of coupled resonators when the total loss of the system is increased.

Harald G. L. Schwefel
Senior Lecturer Physics

I work on Resonat Optics.