Suppression of Superluminous Precursors in High-Power Backward Raman Amplifiers

Tsidulko, Yu. A.; Malkin, V. M.; Fisch, Nathaniel J.

doi:10.1103/physrevlett.88.235004

Cited by 69 publications

(50 citation statements)

References 16 publications

(11 reference statements)

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“…pe , the efficiency can be as high as 90%. What makes the resonant Raman backscatter regime attractive is that it is a simple resonant interaction, with the seed amplification strong enough to outrun other deleterious competing instabilities (such as modulational instability that can lead to the filamentation of the laser beam) [6] or to avoid superluminous precursor solutions [8], and with realizable highly compressed ultrashort pulse solutions [9].The Raman backscattering (RBS) amplification can be divided into linear and nonlinear regimes. In the linear regime the pump depletion is negligible and the gain is independent of the seed intensity.…”

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Reaching the Nonlinear Regime of Raman Amplification of Ultrashort Laser Pulses

et al. 2005

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The intensity of a subpicosecond laser pulse was amplified by a factor of up to 1000 using the Raman backscatter interaction in a 2 mm long gas jet plasma. The process of Raman amplification reached the nonlinear regime, with the intensity of the amplified pulse exceeding that of the pump pulse by more than an order of magnitude. Features unique to the nonlinear regime such as gain saturation, bandwidth broadening, and pulse shortening were observed. Simulation and theory are in qualitative agreement with the measurements. The invention of chirped pulse amplification (CPA) [1,2] led to a tremendous increase of ultrashort laser pulse intensities to above 10 20 W=cm 2 [3,4]. However, such an ultrahigh intensity laser system was achieved using very large (on the order of 1 m 2 ) and expensive compressor gratings [4]. A further increase of the pulse intensity using the CPA technique would require even larger gratings in order not to exceed the material damage threshold. Such a system would be very difficult to implement in universityscale laboratories.In order to overcome the CPA material limit at ultrahigh intensities, different backscattering coupling techniques were proposed in plasma, including Compton scattering [5], resonant Raman backscattering [6], and Raman backscattering at an ionization front [7]. The experiments reported here utilize the resonant Raman mechanism [6], where a short seed laser pulse is amplified by a counterpropagating long pump pulse, with their frequencies satisfying the resonance relation, ! pump ! seed ! pe where ! pump , ! seed , and ! pe are frequencies of pump, seed, and plasma, respectively; ! pe 4 e 2 n e =m e p , n e is the plasma electron density, and m e and e are mass and charge of an electron. The energy transfer from pump to seed is in proportion to their frequencies, so for ! pump 10! pe , the efficiency can be as high as 90%. What makes the resonant Raman backscatter regime attractive is that it is a simple resonant interaction, with the seed amplification strong enough to outrun other deleterious competing instabilities (such as modulational instability that can lead to the filamentation of the laser beam) [6] or to avoid superluminous precursor solutions [8], and with realizable highly compressed ultrashort pulse solutions [9].The Raman backscattering (RBS) amplification can be divided into linear and nonlinear regimes. In the linear regime the pump depletion is negligible and the gain is independent of the seed intensity. The seed pulse is amplified and increased in duration due to the narrow bandwidth of the linear amplification. The nonlinear regime, the socalled -pulse regime, is characterized by pump depletion and the simultaneous temporal compression of the amplified pulse. In this regime, the Raman amplification and compression of ultrashort pulses in a plasma allow intensities to reach 10 20 -10 21 W=cm 2 in a compact universityscale device, and unprecedented high intensity on the order of 10 25 W=cm 2 in a larger system [9]. Such intensities open new frontiers i...

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Reaching the Nonlinear Regime of Raman Amplification of Ultrashort Laser Pulses

et al. 2005

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“…However, since they require a precise resonance, they may also be selectively extinguished through detuning. 30 Random density inhomogeneities may defocus the pumped pulse, but the pulse tends to average over the density fluctuations if there are many correlation lengths within the plasma. 31 Because of this averaging, only some of the signal is deflected, and the phase front of the majority of the signal remains intact and focusable.…”

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Generation of Ultra-high Intensity Laser Pulses

Fisch¹,

Malkin²

2003

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Mainly due to the method of chirped pulse amplification, laser intensities have grown remarkably during recent years. However, the attaining of very much higher powers is limited by the material properties of gratings. These limitations might be overcome through the use of plasma, which is an ideal medium for processing very high power and very high total energy. A plasma can be irradiated by a long pump laser pulse, carrying significant energy, which is then quickly depleted in the plasma by a short counterpropagating pulse. This counterpropagating wave effect has already been employed in Raman amplifiers using gases or plasmas at low laser power. Of particular interest here are the new effects which enter in high power regimes. These new effects can be employed so that one high-energy optical system can be used like a flashlamp in what amounts to pumping the plasma, and a second low-power optical system can be used to extract quickly the energy from the plasma and focus it precisely. The combined system can be very compact. Thus, focused intensities more than 10 25 W/cm 2 can be contemplated using existing optical elements. These intensities are several orders of magnitude higher than what is currently available through chirped pump amplifiers.

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“…This results in the appearance of a small-scale transverse modulation of the amplified pulse and thus leads to poor focusability of the latter. Also, as an intense pump with a fixed frequency passes through plasma, thermal Langmuir fluctuations [2,3]and seed precursors are amplified by the same Raman mechanism being used for the desired signal amplification [4]. The precursor can absorb a significant part of the pump energy.…”

Section: Introductionmentioning

confidence: 99%

Noise suppression and enhanced focusability in plasma Raman amplifier with multi-frequency pump

et al. 2003

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Laser pulse compression/amplification through Raman backscattering in plasmas can be facilitated by using multi-frequency pump laser beams. The efficiency of amplification is increased by suppressing the Raman instability of thermal fluctuations and seed precursors. Also the focusability of the amplified radiation is enhanced due to the suppression of large-scale longitudinal speckles in the pump wave structure.

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Suppression of Superluminous Precursors in High-Power Backward Raman Amplifiers

Cited by 69 publications

References 16 publications

Reaching the Nonlinear Regime of Raman Amplification of Ultrashort Laser Pulses

Reaching the Nonlinear Regime of Raman Amplification of Ultrashort Laser Pulses

Generation of Ultra-high Intensity Laser Pulses

Noise suppression and enhanced focusability in plasma Raman amplifier with multi-frequency pump

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