Cascading amplified spontaneous emission of NO Rydberg states

Amplified spontaneous emission (ASE) from single rotational levels of the Rydberg states (3dσ,π)H ²Σ⁺, H′ ²Π(v=1), (4pσ)M ²Σ⁺(v=0), (4pπ)K ²Π(v=1), (4dσ,π)O ²Σ⁺, O′ ²Π(v=0), 4f(v=1), and (5sσ)S ²Σ⁺(v=0) of nitric oxide, populated through optical–optical double resonance excitation has been observed. The ultraviolet laser is fixed to a specific rotational component of the A ²Σ⁺(v′=0 and 1)←X ²Π_3/2(v″=0) transitions of NO. When the second visible laser was introduced collinearly and the frequency was resonant to the transitions from the A ²Σ⁺ state to the higher Rydberg states, the highly directional ASE in the near infrared region was found to be generated along the excitation laser beams. ASE excitation spectra exhibit an excellent signal‐to‐noise ratio, demonstrating the usefulness of the laser‐induced ASE as a novel spectroscopic technique for excited states of molecules. Dispersed ASE spectra revealed the cascading radiative decay from the initially populated levels down to the A ²Σ⁺ state. The rotational dependence of the ASE pattern as well as the effect of a perturbation between Rydberg and valence states were briefly discussed.