Few-cycle optical probe-pulse for investigation of relativistic laser-plasma interactions

Schwab, M. B.; Sävert, Alexander; Jäckel, O.; Polz, J.; Schnell, M.; Rinck, T.; Veisz, László; Möller, Max; Hansinger, P.; Paulus, G. G.; Kaluza, Malte C.

doi:10.1063/1.4829489

Cited by 36 publications

(28 citation statements)

References 20 publications

(27 reference statements)

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“…A small fraction of the laser was split from the main pulse, spectrally broadened in a hollow-core fiber filled with argon to support a transform limited pulse duration of τ FL = 4.4 fs. Using dispersive mirrors and glass wedges to optimize dispersion, probe pulses as short as τ probe = (5.9 ± 0.4) fs were created [26]. These synchronized, few-cycle probe pulses were used to back-light the LWFA perpendicularly to the pump-pulse direction.…”

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confidence: 99%

Direct Observation of the Injection Dynamics of a Laser Wakefield Accelerator Using Few-Femtosecond Shadowgraphy

et al. 2015

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We present few-femtosecond shadowgraphic snapshots taken during the non-linear evolution of the plasma wave in a laser wakefield accelerator with transverse synchronized few-cycle probe pulses. These snapshots can be directly associated with the electron density distribution within the plasma wave and give quantitative information about its size and shape. Our results show that self-injection of electrons into the first plasma wave period is induced by a lengthening of the first plasma period. Three dimensional particle in cell simulations support our observations.Laser-wakefield accelerators (LWFA) operating in the 'bubble'-regime [1] can generate quasimonoenergetic multigigaelectronvolt electron beams [2,3] with femtosecond duration [4,5] and micrometer dimensions [6,7]. These beams are produced by accelerating electrons in laser-driven plasma waves over centimeter distances. They have the potential to be compact alternatives to conventional accelerators [8]. In a LWFA, the short driving laser pulse displaces plasma electrons from the stationary background ions. The generated space charge fields cause the electrons to oscillate and form a plasma wave in the laser's wake. This wave follows the laser at almost c, the speed of light; for low amplitude it has a wavelength ofwhere n e is the electron density of the plasma. At high amplitude, electrons from the background can be injected into the wake and accelerated, producing monoenergetic electron pulses [9][10][11]. Significant progress has been made regarding achievable peak energy [3], beam stability [12] and the generation of bright X-ray pulses [13][14][15]. Until now, most of our knowledge about the dynamics of the self-injection process has been derived from detailed particle-in-cell (PIC) simulations. These simulations show that self-focusing [16] and pulse compression [17] play a vital role in increasing the laser pulse intensity prior to injection. Furthermore, simulations indicate that self-injection of electrons is associated with a dynamic lengthening of the first plasma wave's period (the 'bubble'). This lengthening can be driven by changes of the electric field structure inside the plasma wave caused by the injected electrons [18]. In contrast, the lengthening may also be due to an intensity amplification of the laser pulse caused by the non-linear evolution of the plasma wave [19,20] or due to a local increase in intensity caused by two colliding pulses [21]. In these latter scenarios, injection is a consequence of the lengthening of the bubble. However, experimental insight into these processes is extremely challenging due to the small spatial and temporal scales of a LWFA.The plasma wave, a variation in the electron density, has an associated refractive index profile which can be detected using longitudinal [22][23][24] or transverse probes [5]. Longitudinal probes cannot measure the rapid and dynamic evolution of the plasma wave that occurs in nonlinear wakefield accelerators and suffer from the strong refraction caused by the steep refractive ...

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Direct Observation of the Injection Dynamics of a Laser Wakefield Accelerator Using Few-Femtosecond Shadowgraphy

et al. 2015

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“…The optimal electron density for acceleration within the cell was measured to be n e;LWFA ¼ ð1.0 AE 0.25Þ × 10 19 cm −3 using interferometry. The density was cross checked by measuring the plasma wavelength by transverse optical probing [41]. Typical electron spectra for our laser and plasma conditions show an energy between 100 and 150 MeV and an energy spread down to <20 MeV with a total charge of up to a few pC.…”

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confidence: 99%

Demonstration of passive plasma lensing of a laser wakefield accelerated electron bunch

Kuschel

Hollatz

Heinemann

et al. 2016

Phys. Rev. Accel. Beams

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We report on the first demonstration of passive all-optical plasma lensing using a two-stage setup. An intense femtosecond laser accelerates electrons in a laser wakefield accelerator (LWFA) to 100 MeV over millimeter length scales. By adding a second gas target behind the initial LWFA stage we introduce a robust and independently tunable plasma lens. We observe a density dependent reduction of the LWFA electron beam divergence from an initial value of 2.3 mrad, down to 1.4 mrad (rms), when the plasma lens is in operation. Such a plasma lens provides a simple and compact approach for divergence reduction well matched to the mm-scale length of the LWFA accelerator. The focusing forces are provided solely by the plasma and driven by the bunch itself only, making this a highly useful and conceptually new approach to electron beam focusing. Possible applications of this lens are not limited to laser plasma accelerators. Since no active driver is needed the passive plasma lens is also suited for high repetition rate focusing of electron bunches. Its understanding is also required for modeling the evolution of the driving particle bunch in particle driven wake field acceleration.

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“…The output spectrum has its maximum at 840 nm, and a substantial part of the total energy of (120 ± 20) μJ can be found in a range of 600-920 nm. At the exit of the fiber a set of chirped mirrors compresses the pulses down to (5.9 ± 0.4) fs [26] under optimized conditions. However, in this experiment the pulses were not compressed to their bandwidth limit due to additional dispersion in the experimental setup.…”

Section: Methodsmentioning

confidence: 99%

Broadband stimulated Raman backscattering

et al. 2016

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Broadband amplification employing stimulated Raman backscattering is demonstrated. Using seed pulses with a bandwidth of about 200 nm, we study the amplification in a wide spectral range in a single laser shot. With chirped pump pulses and a Ne gas jet, we observed under optimized conditions, amplification in a range of about 80 nm, which is sufficient to support the amplification of sub-20 fs pulses. This broad amplification range is also in excellent agreement with PIC simulations. The conversion efficiency is at certain wavelengths as high as 1.2% and was measured to be better than 6×10 −3 on average.

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Few-cycle optical probe-pulse for investigation of relativistic laser-plasma interactions

Cited by 36 publications

References 20 publications

Direct Observation of the Injection Dynamics of a Laser Wakefield Accelerator Using Few-Femtosecond Shadowgraphy

Direct Observation of the Injection Dynamics of a Laser Wakefield Accelerator Using Few-Femtosecond Shadowgraphy

Demonstration of passive plasma lensing of a laser wakefield accelerated electron bunch

Broadband stimulated Raman backscattering

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