Backward Raman Amplification in a Plasma Waveguide

Pai, Chih-Hao; Lin, Ming; Ha, L.-C.; Huang, Shing-Tsaan; Tsou, None Yun-Chin; Chu, H.-H.; Lin, Jiunn‐Yuan; Wang, J.; Chen, S.-Y.

doi:10.1103/physrevlett.101.065005

Cited by 62 publications

(22 citation statements)

References 17 publications

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“…These effects likely contribute to the low efficiencies reported by experimental campaigns [6][7][8][9], the best to date being by Ren et al, achieving 6.4% in a double-pass setup [10]. Previous theoretical and computational works have focussed on the optimal pump amplitude for efficient amplification [2,5,11,12].…”

Section: Introductionmentioning

confidence: 99%

Raman amplification in the coherent wave-breaking regime

Farmer¹,

Pukhov²

2015

Phys. Rev. E

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In regimes far beyond the wavebreaking threshold of Raman amplification, we show that significant amplifcation can occur after the onset of wavebreaking, before phase mixing destroys the coherent coupling between pump, probe and plasma wave. Amplification in this regime is therefore a transient effect, with the higher-efficiency "coherent wavebreaking" (CWB) regime accessed by using a short, intense probe. Parameter scans illustrate the marked difference in behaviour between below wavebreaking, in which the energy-transfer efficiency is high but total energy transfer is low, wavebreaking, in which efficiency is low, and CWB, in which moderate efficiencies allow the highest total energy transfer.

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Section: Introductionmentioning

confidence: 99%

Raman amplification in the coherent wave-breaking regime

Farmer¹,

Pukhov²

2015

Phys. Rev. E

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“…We propose that this stage can be avoided by starting the amplifier at the focus, maximising the effectiveness of the seed. Although some previous studies have used small spot sizes in plasma waveguides 40,41 , the allowable pump energy is then constrained by the small plasma volume. The new diverging geometry increases the allowable pump energy while retaining the minimal seed pulse requirements.…”

Section: Discussionmentioning

confidence: 99%

Advantages to a diverging Raman amplifier

Sadler¹,

Silva²,

Fonseca³

et al. 2018

Commun Phys

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The plasma Raman instability can efficiently compress a nanosecond long high-power laser pulse to sub-picosecond duration. Although, many authors envisaged a converging beam geometry for Raman amplification, here we propose the exact opposite geometry; the amplification should start at the intense focus of the seed. We generalise the coupled laser envelope equations to include this non-collimated case. The new geometry completely eradicates the usual trailing secondary peaks of the output pulse, which typically lower the efficiency by half. It also reduces, by orders of magnitude, the initial seed pulse energy required for efficient operation. As in the collimated case, the evolution is self similar, although the temporal pulse envelope is different. A two-dimensional particle-in-cell simulation demonstrates efficient amplification of a diverging seed with only 0.3 mJ energy. The pulse has no secondary peaks and almost constant intensity as it amplifies and diverges.

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“…The igniter-heater scheme described above has been used previously for the creation of centimeter-long dense plasma channels in laser wake-field tabletop accelerators and Raman lasers (12,13). We extend this approach to meter-scale plasma channels in ambient air.…”

Section: Lasing Of N 2 and O 2 In Airmentioning

confidence: 99%

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

Hemmer

Miles

Polynkin

et al. 2011

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

150

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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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Backward Raman Amplification in a Plasma Waveguide

Cited by 62 publications

References 17 publications

Raman amplification in the coherent wave-breaking regime

Raman amplification in the coherent wave-breaking regime

Advantages to a diverging Raman amplifier

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

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