Collisional lasing on a self-terminating transition 2 1Po1 – 2 1S0 in helium atom

Lasing on a self-terminating transition 2 ¹P^o₁ – 2 ¹S₀ (λ = 2.058 μm) in helium atom is studied for a single- and double-pulse operation regimes under electron beam pumping in pure helium and its mixtures with H₂, N₂, O₂, CO₂, H₂O, NH₃, and N₂O. In pure helium, the maximal pulse duration is ~50 ns, which agrees with the calculated value. Recovery of lasing in the second pulse is observed at a time delay between the pulses of longer than 1.25 μs. In adding CO₂, N₂O, NH₃, and H₂O, the relaxation rate for population of the metastable state He(2 ¹S₀) increases, which makes the delay, needed for recovering lasing, shorter up to pulse merging in the case of H₂O. At the exciting pulse base-level duration of 1.2 μs, in mixtures of helium with NH₃ and H₂O, laser pulses with a duration of ~0.8 μs are observed, which testifies that collisional quasi-cw lasing occurs. Mechanisms of collisional lasing are discussed.