Coupling ofN2+rotational states in an air laser from tunnel-ionized nitrogen molecules

Abstract

We report on experimental and theoretical investigations of dynamic evolution of individual R-branch laser lines from tunnel-ionized nitrogen molecules based on a pump-probe scheme. Our observation shows that the intensities of the R-branch laser lines exhibit rapid oscillations which can be decomposed into periodic oscillations at different frequencies. The oscillations can be attributed to the coupling between the rotational quantum states mediated either by the probe pulses or by the P -branch laser emission from the molecular ions.

Backward nitrogen lasing actions induced by femtosecond laser filamentation: influence of duration of gain

“…Gain dynamics of lasing actions in N 2 /Ar mixture 2.1. Experimental setup The pump-probe experimental setup for investigating the gain dynamics of nitrogen lasers generated in a gas mixture of N 2 /Ar is schematically illustrated in figure 1, which is similar to that used in our previous works [17,18]. Briefly, femtosecond laser pulses (1 kHz, 800 nm, ∼40 fs) from a commercial Ti: sapphire laser system (Legend Elite Cryo PA, Coherent, Inc.) were divided into two paths with an 80/20 beam splitter (BS).…”

Optical gain in rotationally excited nitrogen molecular ions

“…We point out that high-resolution measurements of rotational spectra of stimulated emission in N + 2 under ultrafast laser pumping have been reported previously [15], but not in connection with the gain mechanism in the N + 2 ions. The focus of Ref.…”

“…The focus of Ref. [15] was on stimulated emission and no spectra of spontaneous emission were reported. Only the difference between stimulated-and spontaneous-emission spectra is indicative of the rotational effect on the optical gain in N + 2 that we discuss below.…”

Ultrafast Rotational Spectroscopy Based on a Free-space Nitrogen Ion Laser

“…The population of the 2 Σ + | ⟩ state is affected by the coupling of | ⟩ ↔ | + 2⟩ which is proportional to the total number of P-branch photons , +1 . Since the P-branch photons from J and 26-J states are indistinguishable because of their same photon energies [6], the P-branch photon number , +1 will be affected by the coupling of |26 − ⟩ ↔ |28 − ⟩, which is related to the population of state 2 Σ + |26 − ⟩. Hence, the time-varying P-branch photon number will leave its signature in the population of 2 Σ + | ⟩ state, namely, the oscillation at the frequency of [4 × (26 − ) − 2] , as indicated in Fig.…”