High-Gain Backward Lasing in Air

Dogariu, Arthur; Michael, James B.; Scully, Marlan O.; Miles, Richard B.

doi:10.1126/science.1199492

Cited by 268 publications

(172 citation statements)

References 17 publications

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“…Naturally, the ability to guide light over microsecond (instead of sub-picosecond, as was the common belief thus far) improves the potential efficiency of power transmission by orders of magnitude. In a similar vein, laser filamentation can give rise to lasing [31,32]. Clearly, having waveguiding effects for extended periods of time would greatly improve applications of these lasing effects.…”

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confidence: 99%

Long-lived waveguides and sound-wave generation by laser filamentation

et al. 2014

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We discover long-lived (microsecond-scale) optical waveguiding in the wake of atmospheric laser filaments. We also observe the formation and then outward propagation of the consequent sound wave. These effects may be used for remote induction of atmospheric long-lived optical structures from afar which could serve for a variety of applications.* These authors contributed equally to this work. 2Propagation of self-guided laser filaments through air and other gases results in a rich variety of phenomena and applications [1][2][3]. A laser filament is formed when a femtosecond pulse, with peak intensity above the critical power for collapse (3 GW in air at an optical wavelength of 800 nm), is propagating in a transparent medium [1]. In air, the diameter of a filament is approximately 100 μm and it can propagate over distances much longer than the Rayleigh length, from 10 cm up to the kilo-meter range [4][5][6][7]. A filament is formed due to a dynamic balance between the linear diffractive and dispersive properties of the medium and its nonlinear features such as self-focusing optical Kerr effect and defocusing due to the free electrons which are released from molecules through multi-photon ionization. In the atmosphere, filaments can be initiated at predefined remote distances [4,5] and propagate through fog, clouds and turbulence [8,9]. Thus, filaments are attractive for atmospheric applications such as remote spectroscopy This mechanism was used for guiding properly delayed picosecond pulses [21,22], but at times larger than several nanosecond after the filamenting pulse, even this process does not leave behind any waveguiding effects. In fact, all processes resulting from plasma or molecular alignment in the wake of atmospheric laser filaments are limited to the first few nanoseconds period. Consequently, it was generally believed that ten nanoseconds after the filament, the medium does not exhibit any waveguiding effect. In contrast to that, it was recently discovered that 0.1-1 milliseconds after the filament, there is a circular negative index change that acts as an antiguide by defocusing a probe beam [23]. This effect was attributed to reduction in the air density at the center of the filament 4 as a result of heating. Altogether, to the best of our knowledge, thus far all experiments and theories on laser filamentation in the atmosphere concluded that there is no longlived (>10 nanosecond) waveguiding effect left behind the femtosecond filamenting pulse. This severely limits any CW application of laser filamentation, because the repetition rate of any high power laser used for creating the filament is low, hence for most of the time between pulses light would not be guided. Likewise, any other potential application would have to "live" on a picosecond scale, because at later times, waveguiding by the filament was thought to be nonexistent.Here, we show the exact opposite: we demonstrate theoretically and experimentally that the filament induces a transient positive index change which lasts for approximate...

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Long-lived waveguides and sound-wave generation by laser filamentation

et al. 2014

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“…Various schemes of turning air into an active laser medium are being investigated [3][4][5][6]. One of the most promising approaches is based on pumping atmospheric nitrogen by ultraintense femtosecond laser pulses propagating in the filamentation regime in air [7].…”

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Optical gain in rotationally excited nitrogen molecular ions

2017

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We pump low-pressure nitrogen gas with ionizing femtosecond laser pulses at 1.5 μm wavelength. The resulting rotationally excited N + 2 molecular ions generate directional, forward-propagating stimulated and isotropic spontaneous emissions at 428 nm wavelength. Through high-resolution spectroscopy of these emissions, we quantify rotational population distributions in the upper and lower emission levels. We show that these distributions are shifted with respect to each other, which has a strong influence on the transient optical gain in this system. Although we find that electronic population inversion exists in our particular experiment, we show that sufficient dissimilarity of rotational distributions in the upper and lower emission levels could, in principle, lead to gain without net electronic population inversion.

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“…Under electric discharge excitation, oxygen has been shown to lase in various spectral lines throughout the UV, visible, and near-IR parts of the spectrum, but in the past lasing was demonstrated only at pressures much lower than atmospheric pressure (16,17). Moreover, we have now made oxygen lase under optical filament excitation at atmospheric pressure (5). Technical realization of neon-oxygen and argon-oxygen lasers offers insights into possible routes to inversion (18,19).…”

Section: Lasing Of N 2 and O 2 In Airmentioning

confidence: 99%

“…Previously, oxygen lasing has been demonstrated only at gas pressures substantially lower than atmospheric pressure. However, oxygen lasing in realistic open-air conditions has now been demonstrated (5). An additional degree of control over optical excitation of atmospheric gases can be offered by spatial beam shaping and adaptive optics.…”

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Standoff spectroscopy via remote generation of a backward-propagating laser beam

Hemmer

Miles

Polynkin

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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In an earlier publication we demonstrated that by using pairs of pulses of different colors (e.g., red and blue) it is possible to excite a dilute ensemble of molecules such that lasing and/or gain-swept superradiance is realized in a direction toward the observer. This approach is a conceptual step toward spectroscopic probing at a distance, also known as standoff spectroscopy. In the present paper, we propose a related but simpler approach on the basis of the backward-directed lasing in optically excited dominant constituents of plain air, N 2 and O 2 . This technique relies on the remote generation of a weakly ionized plasma channel through filamentation of an ultraintense femtosecond laser pulse. Subsequent application of an energetic nanosecond pulse or series of pulses boosts the plasma density in the seed channel via avalanche ionization. Depending on the spectral and temporal content of the driving pulses, a transient population inversion is established in either nitrogen-or oxygen-ionized molecules, thus enabling a transient gain for an optical field propagating toward the observer. This technique results in the generation of a strong, coherent, counterpropagating optical probe pulse. Such a probe, combined with a wavelength-tunable laser signal(s) propagating in the forward direction, provides a tool for various remote-sensing applications. The proposed technique can be enhanced by combining it with the gain-swept excitation approach as well as with beam shaping and adaptive optics techniques.air laser | atmospheric surveillance | threat detection | Raman T he continuous monitoring of the atmosphere for traces of gases and pathogens at kilometer-scale distances is an important and challenging problem, with applications in environmental science and national security. Measurements using light detection and ranging (LIDAR) techniques coupled with differential absorption LIDAR have been reported (1, 2). These techniques provide valuable tools for the measurement of trace impurities in the atmosphere.However, to enhance sensitivity and information content retrieved by the return signal, a different technology is needed. In ref. 3, we presented standoff spectroscopy (SOS) technique for detection of trace impurities in the atmosphere via gain-swept superradiance (4). In that scheme, we first pump the molecules of interest, e.g., nitric oxide or phosgene, at some prearranged distance, say, 300 m. These molecules decay spontaneously to a lower state via a specific radiation frequency. Then the impurity molecules at, say, 290 m, are excited at a later time that is delayed from the first pulse by Δτ ¼ 10m c ≅3 × 10 −8 s, so that some gain is realized in the second region. Subsequent regions of inversion are generated by later pulse pairs as in Fig. 1. In ref. 3, which will be briefly reviewed in Gain-Swept Lasing of Impurities in Air, the impurity molecules themselves constitute the lasing medium. In the present paper, we propose a simpler alternative approach that is based on transient backward-directed lasing i...

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High-Gain Backward Lasing in Air

Cited by 268 publications

References 17 publications

Long-lived waveguides and sound-wave generation by laser filamentation

Long-lived waveguides and sound-wave generation by laser filamentation

Optical gain in rotationally excited nitrogen molecular ions

Standoff spectroscopy via remote generation of a backward-propagating laser beam

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