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

Abstract

We experimentally investigate generation of backward 357 nm N 2 laser in a gas mixture of N 2 /Ar using 800 nm femtosecond laser pulses, and examine the involved gain dynamics based on pumpprobe measurements. Our findings show that a minimum duration of gain in the excited N 2 molecules is required for generating intense backward nitrogen lasers, which is ∼0.8 ns under our experimental conditions. The results shed new light on the mechanism for generating intense backward lasers from nitrogen molecules, which are highly in demand for high sensitivity remote atmospheric sensing application.

Nonperturbative generation of above-threshold harmonics from pre-excited argon atoms in intense mid-infrared laser fields

“…Therefore, it is reasonable to attribute the strong 3rd and 7th harmonic signals generated in our experimental conditions to the nonlinear interaction of the probe beam with the excited-state argon atoms prepared by the intense pump laser pulses. Besides, the temporal evolution of 7th harmonic signal in Figure 2(c) agrees well with our previous observations, providing quantitative evidence on the role of the excited state of argon, i.e., Ar * (4 3 P 2 ) [30] . It is noticed that the photon energy of the 3rd harmonic signal is ∼2 eV, whereas the photon energy of 7th harmonic is ∼4.8 eV.…”

Mid-infrared ultrafast laser pulses induced third harmonic generation in nitrogen molecules on an excited state

“…Recently, free-space air lasing actions induced by intense ultrafast laser pulses have attracted growing attention. On the one hand, the capability of remotely generating intense, narrow-bandwidth, coherent emissions in air opens new horizon for remote sensing 1 2 3 4 5 6 7 8 . On the other hand, as a novel nonlinear optical process, lasing actions in air typically involve complex interplay between various effects in molecules such as dissociation, excitation and ionization of molecules, alignment of neutral and ionized molecules.…”

“…Furthermore, both ground and excited electronic states are involved in the establishment of population inversion responsible to the generation of air lasers. Therefore, efficient generation of air lasers requires preparing the molecules on the excited states with an intense laser field 5 7 8 . Meanwhile, it is equally important to understand the decay dynamics of the excited states for the molecules which serve as the gain medium, which has not been quantitatively examined in a systematic way.…”

“…In the previous investigations, we have demonstrated that air lasers generated with a pump-probe scheme have the ability to probe the ultrafast dynamics of population difference between the upper and lower energy states as lasing typically requires population inversion 7 9 11 . Therefore, the temporal dynamics of air laser signals obtained using the pump-probe scheme cannot provide direct information on the decay dynamics of molecules on excited states.…”

Intensity-independent molecular rotational decoherence lifetimes measured with mean wavelength shifts of femtosecond pulses

“…The pump-probe experimental setup is similar to that used in our previous works [26][27][28] . Briefly, the experiments were performed with a commercial Ti:sapphire laser system (Legend Elite Duo, Coherent, Inc.) which delivers a ∼6 mJ pulse with a central wavelength of 800 nm and pulse duration of 50 fs at a repetition rate of 1 kHz.…”