Lasing Without Inversion in Mercury at 253.7 nm

Principle

The principle of LWI is to cancel the absorption at the laser transition by coherent excitation of adjacent transitions so that only a few excited atoms are sufficient for lasing. Whilst there is no more absorption for coherent light, the laser transition can still be pumped by an incoherent light source like a gas discharge lamp.

Until now there has been no LWI scheme where the laser transition  had a significantly shorter wavelength than the lasers used to build up the coherence.

In our LWI experiment, we use a 4-level-scheme in mercury with a laser transition at 253.7 nm as described in [1]. For this scheme a strong driving laser at 435.6 nm, a weak driving laser at 546.1 nm and an incoherent repump at 404.7 nm are required.

4-level scheme in Hg

References