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Journal of Physics B Atomic Molecular and Optical Physics

Three-photon induced fluorescence and lasing in Ar

Xiaochuang Cui, Haowen Li, Zhihe Dai, Shuo Wang, Xiangxin Xia, Qi Qi, Hongwei Zang, Pengfei Qi, helong li, Weiwei Liu, Huailiang Xu

Published Sep 9, 2026• 0 citations
Publisher

Abstract

Abstract We investigate the fluorescence and lasing emissions in neutral Ar induced by intense femtosecond deep-ultraviolet laser pulses. It is shown that when the pump wavelength is tuned from 260.9 nm to 265.4 nm, the side fluorescence intensities are significantly changed, and the bidirectional cascaded lasing pathway shifts from the transitions of 3d′ 2 [ 5 / 2 ] 3 o →4p′ 2 [ 3 / 2 ] 2 and 4p′ 2 [ 3 / 2 ] 2 →4s 2 [ 1 / 2 ] 1 o (yielding the 1327 and 840 nm lasing emissions) to the transitions of 3d 2 [ 7 / 2 ] 3 o →4p 2 [ 5 / 2 ] 2 and 4p 2 [ 5 / 2 ] 2 →4s 2 [ 3 / 2 ] 1 o (yielding the 1350 and 842 nm emissions). By recording fluorescence intensity dependence on the p

DOI
10.1088/1361-6455/aea532

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Abstract We investigate the fluorescence and lasing emissions in neutral Ar induced by intense femtosecond deep-ultraviolet laser pulses. It is shown that when the pump wavelength is tuned from 260.9 nm to 265.4 nm, the side fluorescence intensities are significantly changed, and the bidirectional cascaded lasing pathway shifts from the transitions of 3d′ 2 [ 5 / 2 ] 3 o →4p′ 2 [ 3 / 2 ] 2 and 4p′ 2 [ 3 / 2 ] 2 →4s 2 [ 1 / 2 ] 1 o (yielding the 1327 and 840 nm lasing emissions) to the transitions of 3d 2 [ 7 / 2 ] 3 o →4p 2 [ 5 / 2 ] 2 and 4p 2 [ 5 / 2 ] 2 →4s 2 [ 3 / 2 ] 1 o (yielding the 1350 and 842 nm emissions). By recording fluorescence intensity dependence on the p
Cavity-free lasing in atmospheric air has stimulated intense research toward a fundamental understanding of underlying physical mechanisms. In this Letter, we identify a new mechanism-a third-harmonic photon mediated resonant energy transfer pathway leading to population inversion in argon via an initial three-photon excitation of nitrogen molecules irradiated by intense 261 nm pulses-that enables bidirectional two-color cascaded lasing in atmospheric air. By making pump-probe measurements, we conclusively show that such cascaded lasing results from superfluorescence rather than amplified spontaneous emission. Such cascaded lasing with the capability of producing bidirectional multicolor coherent pulses opens additional possibilities for remote sensing applications.
Lasing refers to the generation of highly directional laser-like emission remotely pumped by laser pulses in a medium such as ambient air or a flame.It has been intensively investigated because of its potentials to revolutionize the field of remote sensing.Earlier studies were carried out in flames, where lasing effect has been observed in various radicals, for example H, O, N etc., through two-photon resonant excitation.This scheme was later applied to generate lasing of O and N in ambient air, which can be dramatically improved by predissociation of the air constituents.However, the underlying physical mechanism of two-photon-excited lasing effect is still unsettled although it has been studied for more than one decade.Currently there are three different proposals: (1) Amplified Spontaneous Emission (ASE), in which case population inversion is responsible for optical gain;(2) Superfluorescence (SF), where a macroscopic dipole occurs in the population inverted medium; (3) Both hyper-Raman scattering and four-wave mixing are involved in the generation of lasing emission.Here, we experimentally studied 656 nm lasing emission of atomic hydrogen via two-photon resonant excitation by focusing 125-fs laser pulses of 205-nm wavelength in a methane/oxygen welding flame (see Fig. 1), where hydrogen atoms are naturally present.Lasing occurs in both forward and backward directions, and the forward signal strength is almost one order of magnitude stronger than the backward one.It has been found that the durations of lasing pulses are around 20 ps, and decreases with increasing pump laser energies.Furthermore, the delay of the lasing pulse with respect to the pump pulse decreases with increasing pump energies.These results show high similarities with the behaviors of SF, suggesting that the femtosecond two-photonexcited lasing emission of atomic hydrogen might be SF.
Pulsed lasing from optically pumped rare gas metastable atoms (Ne, Ar, Kr, and Xe) has been demonstrated previously. The laser relies on a three-level scheme, which involves the (n+1)p[5/2](3) and (n+1)p[1/2](1) states from the np(5)(n+1)p electronic configuration and the metastable (n+1)s[3/2](2) level of the np(5)(n+1)s configuration (Racah notation). Population inversions were achieved using relaxation from ((n+1)p[5/2](3) to (n+1)p[1/2](1) induced by collisions with helium or argon at pressures near 1 atm. Pulsed lasing was easily achieved using the high instantaneous pump intensities provided by a pulsed optical parametric oscillator excitation laser. In the present study we examine the potential for the development of a continuous wave (CW) optically pumped Ar laser. We report lasing of the 4p[1/2](1)→4s[3/2](2) (912.547 nm) transition following CW diode laser excitation of the 4p[5/2](3)←4s[3/2](2) line (811.754 nm). A pulsed discharge was used to generate Ar 4s[3/2](2), and the time-resolved lasing kinetics provide insights concerning the radiative and collisional relaxation processes.
Argon gas excited by resonant femtosecond ultraviolet pulses gives rise to cavity-free lasing emission in the near-infrared (NIR) range. Here we reported on a pump-probe study of the optical gain of this lasing phenomenon. With the injection of an external seeding pulse, the forward signal was significantly enhanced, confirming the existence of optical gain. The temporal dynamics of the optical gain were characterized by a time-resolved measurement. It was found that the optical gain decays on a time scale of ∼ 10 ps and it does not present a significant dependence on the gas pressures. Moreover, the intensity of the forward NIR emission signal shows a linear dependence on the gas pressure. These features suggest that the nature of this forward NIR radiation is amplified spontaneous emission, not superradiance when multiple-photon resonant excitation is involved.
i n Ùnal for m Marc h 1, 2001) W e rep ort results of investigation on the Ûuorescence induced in sodium v ap our by pulses of laser light tuned near the 3 S ! 4 P transition (330 nm ).T he Ûuorescence w as observed in perp endi cular and parallel direction s in resp ect to the laser b eam.A depletion of Ûuorescence intensity corresp ondin g to the 5 D ! 3 P transition (498 nm) was observed along the laser beam.W e explain this e˜ect as a result of reabsorption that is caused by intense p opulati on of the 3 P level due to cascade stimulated pro cesses.T he most intense depletio n occurs ab out 20 ns after the laser pulse and it corresp onds to the moment of maximal populati on of the 3 P level.