Pulse Front Sharpening of a Laser Beam in Plasma

Upadhyay, A.; Tripathi, V. K.; Pant, H. C.

doi:10.1238/physica.regular.063a00326

Cited by 11 publications

(9 citation statements)

References 9 publications

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“…Faure et al (2005) have reported pulse front sharpening that is confirmed by three-dimensional (3D) particle-in-cell simulations. Upadhyay et al (2001) have developed an analytical theory for it.…”

Section: Introductionmentioning

confidence: 99%

Relativistic self-distortion of a laser pulse and ponderomotive acceleration of electrons in an axially inhomogeneous plasma

2010

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Relativistic self distortion of a Gaussian laser pulse in inhomogeneous plasma in one dimension is investigated. The relativistic mass effect causes different portions of the pulse to travel with different group velocities leading to the steepening of the pulse front and broadening of the rear. This asymmetry created in the pulse shape gives rise to stronger ponderomotive force on electrons at the front and weaker at the rear. The fast moving electrons under this force are shown to have very significant net energy gain. The energy gain increases with the density scale-length and then saturates.

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Section: Introductionmentioning

confidence: 99%

Relativistic self-distortion of a laser pulse and ponderomotive acceleration of electrons in an axially inhomogeneous plasma

2010

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“…The pulse then must propagate through this 'pre-plasma' before being reflected at the critical density interface, becoming subject to non-linear instabilities that result in spectral [42], temporal [43] and spatial [44] distortions, creating significantly different pulse characteristics and driving additional (often less predictable) shot-to-shot variations. The presence of pre-plasma also introduces additional magnetic field generation mechanisms [44][45][46], resulting in quasi-static hundreds of MegaGauss fields that can extend over microns and persist throughout the interaction which can perturb, or even trap, relativistic electron trajectories.…”

Section: Issues Typical Of Ultra-intense Laser-plasma Interactionsmentioning

confidence: 99%

“…1 The change in divergence between the incident and specularly reflected pulse, due to the shape of the relativistic critical surface, has been shown to be a strong indicator of pre-plasma scale length near critical density [78]. Instantaneous spectral shifting and broadening due to motion of the critical surface [35] and relativistic effects [42] have been observed to be quite sensitive to pre-plasma environment, as well as temporal pulse front steepening due to group velocity dispersion [43]. Spatial, spectral and polarimetry measurements of harmonics generated near the critical surface have been found to sensitive to pulse contrast [79] and target surface roughness [80,81] as well as indicative of magnetic fields in the under-dense pre-plasma environment [82,83].…”

Section: Experimental Technique Limitationsmentioning

confidence: 99%

“…The peak of the pulse has a higher γ than the wings, and with a higher index of refraction. In under-dense plasma, the peak of the pulse can travel faster than the leading or trailing edges, resulting in temporal pulse front sharpening [43], illustrated in Figure 1.9(a). The difference in the time required for a relativistic pulse of to travel to the critical density (indicated by x c ) is given by Equation 1.33: negative values of ∆t, like those for γ > 1 for relativistic intensities, implies that the front of the pulse would sharpen and conversely, positive values would imply that the trailing edge of the pulse would sharpen.…”

Section: Temporal/spatial Envelope Modificationsmentioning

confidence: 99%

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Specular Reflectivity and Hot-Electron Generation in High-Contrast Relativistic Laser-Plasma Interactions

Kemp

2013

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Ultra-intense laser (> 10 18 W/cm 2 ) interactions with matter are capable of producing relativistic electrons which have a variety of applications in state-of-the-art scientific and medical research conducted at universities and national laboratories across the world. Control of various aspects of these hot-electron distributions is highly desired to optimize a particular outcome. Hot-electron generation in low-contrast interactions, where significant amounts of under-dense pre-plasma are present, can be plagued by highly non-linear relativistic laser-plasma instabilities and quasi-static magnetic field generation, often resulting in less than desirable and predictable electron source characteristics. High-contrast interactions offer more controlled interactions but often at the cost of overall lower coupling and increased sensitivity to initial target conditions. An experiment studying the differences in hot-electron generation between high and low-contrast pulse interactions with solid density targets was performed on the Titan laser platform at the Jupiter Laser Facility at Lawrence Livermore National Laboratory in Livermore, CA. To date, these hot-electrons generated in the laboratory are not directly observable at the source of the interaction. Instead, indirect studies are performed using state-of-the-art simulations, constrained by the various experimental measurements. These measurements, more-often-than-not, rely on secondary processes generated by the transport of these electrons through the solid density materials which can susceptible to a variety instabilities and target material/geometry effects. Although often neglected in these types of studies, the specularly reflected light can provide invaluable insight as it is directly influenced by the interaction.In this thesis, I address the use of (personally obtained) experimental specular reflectivity measurements to indirectly study hot-electron generation in the context of high-contrast, ii relativistic laser-plasma interactions. Spatial, temporal and spectral properties of the incident and specular pulses, both near and far away from the interaction region where experimental measurements are obtained, are used to benchmark simulations designed to infer dominant hot-electron acceleration mechanisms and their corresponding energy/angular distributions. To handle this highly coupled interaction, I employed particle-in-cell modeling using a wide variety of algorithms (verified to be numerically stable and consistent with analytic expressions) and physical models (validated by experimental results) to reasonably model the interaction's sweeping range of plasma densities, temporal and spatial scales, G. E. Kemp, et al, Experimental and LSP modeling of pre-pulse effects on the laser-plasma interaction by a 527 nm laser pulse,

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“…atto-second duration) pulses, self-focusing, pulse modification, stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS) and the like. In an earlier study pulse front sharpening of an intense short Gaussian pulse laser propagating in plasma has been studied when quiver velocity of the electron approaches the velocity of light [22]. However, this study refers to many-cycle pulses and does not take into account the CE phase associated with few-cycle or single-cycle pulse propagation.…”

Section: Introductionmentioning

confidence: 99%

Analytical and numerical investigation of diffraction effects on the nonlinear propagation of ultra-intense few-cycle optical pulses in plasmas

et al. 2009

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The propagation of intense few-cycle laser beams in plasma media is considered when the quiver velocity of the electron approaches the velocity of light c. The modifications in the spatio-temporal profile of the initial Gaussian beam are found to depend on the combined effect of relativistic plasma frequency and diffraction. The results of the variation of the temporal profile of the envelope at points on the axis as well away from the axis are presented. The results so obtained are compared with those of vacuum propagation. Pulses get broadened and frequency gets chirped as a result of diffraction, phase dispersion and relativistic mass correction. The effect of the plasma on the group velocity dispersion including curvatures of pulse and phase fronts in pulsed Gaussian beam is numerically investigated.

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Pulse Front Sharpening of a Laser Beam in Plasma

Cited by 11 publications

References 9 publications

Relativistic self-distortion of a laser pulse and ponderomotive acceleration of electrons in an axially inhomogeneous plasma

Relativistic self-distortion of a laser pulse and ponderomotive acceleration of electrons in an axially inhomogeneous plasma

Specular Reflectivity and Hot-Electron Generation in High-Contrast Relativistic Laser-Plasma Interactions

Analytical and numerical investigation of diffraction effects on the nonlinear propagation of ultra-intense few-cycle optical pulses in plasmas

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