Destructive interference in N2+ lasing

We report an unexpected experimental observation in rotation-resolved N+2 lasing that the R-branch lasing intensity from a single rotational state in the vicinity of 391 nm can be greatly stronger than the P-branch lasing intensity summing over the total rotational states at suitable pressures. According to a combined measurement of the dependence of the rotation-resolved lasing intensity on the pump-probe delay and the rotation-resolved polarization, we speculate that the destructive interference can be induced for the spectrally-indistinguishable P-branch lasing due to the propagation effect while the R-branch lasing is little affected due to its discrete spectral property, after precluding the role of rotational coherence. These findings shed light on the air-lasing physics, and provide a feasible route to manipulate air lasing intensity.

Automated summary

In rotation-resolved N+2 lasing, we observe an unexpected experimental phenomenon that the R-branch lasing intensity from a single rotational state near 391 nm can be much stronger than the sum of P-branch lasing intensities from all rotational states at suitable pressures. Through combined measurements of the dependence of rotation-resolved lasing intensity on pump-probe delay and rotation-resolved polarization, we speculate that the destructive interference may occur for spectrally-indistinguishable P-branch lasing due to propagation effect, while R-branch lasing is minimally affected due to its discrete spectral property, after ruling out the role of rotational coherence. These findings shed light on the physics of air lasing and provide a feasible approach to manipulate air lasing intensity.