High harmonic generation in the relativistic limit

Dromey, B.; Zepf, Matthew; Gopal, A.; Lancaster, K. L.; Wei, M. S.; Krushelnick, K.; Tatarakis, M.; Vakakis, N.; Moustaizis, S.; Kodama, R.; Tampo, M.; Stoeckl, C.; Clarke, R. J.; Habara, H.; Neely, D.; Karsch, Stefan; Norreys, P.

doi:10.1038/nphys338

Cited by 463 publications

(296 citation statements)

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“…Dense, femtosecond-laser-produced plasmas hold promise of converting laser light into coherent harmonics with much higher efficiency and of exploiting much higher laser intensities, because the plasma medium-in contrast to the atomic emitters-imposes no restriction on the strength of the laser field driving the harmonics [6][7][8][9][10][11][12][13] . Recent experimental studies of harmonics produced from overdense plasmas impressively corroborate several theoretical predictions: the high conversion efficiency 19 , the favourable scalability of the generation technique towards high photon energies 14,16,19 and excellent divergence due to the spatial coherence of the generated harmonics 19,22 . Whether the high-order harmonics that are produced in overdense plasmas • gold-coated off-axis parabolic mirror with the same focal length as the laser focusing parabola.…”

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confidence: 51%

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Attosecond phase locking of harmonics emitted from laser-produced plasmas

et al. 2008

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Laser-driven coherent extreme-ultraviolet (XUV) sources provide pulses lasting a few hundred attoseconds 1,2 , enabling real-time access to dynamic changes of the electronic structure of matter 3,4 , the fastest processes outside the atomic nucleus. These pulses, however, are typically rather weak. Exploiting the ultrahigh brilliance of accelerator-based XUV sources 5 and the unique time structure of their laser-based counterparts would open intriguing opportunities in ultrafast X-ray and high-field science, extending powerful nonlinear optical and pump-probe techniques towards X-ray frequencies, and paving the way towards unequalled radiation intensities. Relativistic laser-plasma interactions have been identified as a promising approach to achieve this goal 6-13 . Recent experiments confirmed that relativistically driven overdense plasmas are able to convert infrared laser light into harmonic XUV radiation with unparalleled efficiency, and demonstrated the scalability of the generation technique towards hard X-rays 14-19 . Here we show that the phases of the XUV harmonics emanating from the interaction processes are synchronized, and therefore enable attosecond temporal bunching. Along with the previous findings concerning energy conversion and recent advances in high-power laser technology, our experiment demonstrates the feasibility of confining unprecedented amounts of light energy to within less than one femtosecond.The nonlinear response of matter exposed to intense femtosecond laser pulses gives rise to the emission of highfrequency radiation at harmonics of the laser oscillation frequency. If the harmonics are phase-locked, their superposition results in a train of attosecond bursts 20 . The concept has been so far successfully implemented in atomic gases 21 , and culminated in isolated attosecond pulses by using few-cycle laser drivers 1,2 . The low generation efficiency of harmonic radiation from atoms has motivated research into alternative concepts. Dense, femtosecond-laser-produced plasmas hold promise of converting laser light into coherent harmonics with much higher efficiency and of exploiting much higher laser intensities, because the plasma medium-in contrast to the atomic emitters-imposes no restriction on the strength of the laser field driving the harmonics [6][7][8][9][10][11][12][13] . Recent experimental studies of harmonics produced from overdense plasmas impressively corroborate several theoretical predictions: the high conversion efficiency 19 , the favourable scalability of the generation technique towards high photon energies 14,16,19 and excellent divergence due to the spatial coherence of the generated harmonics 19,22 . Whether the high-order harmonics that are produced in overdense plasmas • gold-coated off-axis parabolic mirror with the same focal length as the laser focusing parabola. The recollimating mirror is mounted on a flipper stage for easy withdrawal, thus enabling the spectral characterization of the emitted XUV light. Thin metal filters (typically 150 nm Al, In or Sn)...

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confidence: 51%

“…The result motivates advancement of multiterawatt few-cycle laser technology 28 , particularly in providing sufficiently high-contrast laser pulses as an alternative to the use of plasma mirrors 16,17 . This will lead to isolated subfemtosecond pulses with peak intensities rivalling those produced by accelerator-based sources 5 .…”

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confidence: 99%

Attosecond phase locking of harmonics emitted from laser-produced plasmas

et al. 2008

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“…Due to these remarkable properties, plasma mirrors are now largely used in ultrafast optics as a single-shot high-intensity optical device, e.g. to improve temporal contrast of femtosecond pulses [24], for the tight focusing of ultraintense beams [26], or for the generation of high-order harmonics and attosecond pulses [27,28].…”

Section: Plasma Mirrors As Electron Injectorsmentioning

confidence: 99%

Vacuum laser acceleration of relativistic electrons using plasma mirror injectors

et al. 2015

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Accelerating particles to relativistic energies over very short distances using lasers has been a long standing goal in physics. Among the various schemes proposed for electrons, vacuum laser acceleration has attracted considerable interest and has been extensively studied theoretically because of its appealing simplicity: electrons interact with an intense laser field in vacuum and can be continuously accelerated, provided they remain at a given phase of the field until they escape the laser beam. But demonstrating this effect experimentally has proved extremely challenging, as it imposes stringent requirements on the conditions of injection of electrons in the laser field. Here, we solve this long-standing experimental problem for the first time by using a plasma mirror to inject electrons in an ultraintense laser field, and obtain clear evidence of vacuum laser acceleration.With the advent of PetaWatt class lasers, this scheme could provide a competitive source of very high charge (nC) and ultrashort relativistic electron beams.1 arXiv:1511.05936v1 [physics.plasm-ph] 18 Nov 2015Femtosecond lasers currently achieve light intensities at focus that far exceed 10 18 W/cm 2 at near infrared wavelengths [1]. One of the great prospects of these extreme intensities is the laser-driven acceleration of electrons to relativistic energies within very short distances.At present, the most advanced scheme consists of using ultraintense laser pulses to excite large amplitude wakefields in underdense plasmas, providing extremely high accelerating gradients in the order of 100 GV/m [2]. However, over the past decades, the direct acceleration of electrons by light in vacuum has also attracted considerable interest and has been extensively studied theoretically [3][4][5][6][7][8][9][10][11]. These investigations have been driven by the fundamental interest of this most elementary interaction, and by its potential for extreme electron acceleration through electric fields of > 10's TV/m that ultraintense laser pulses provide.The underlying idea is to inject free electrons into an ultraintense laser field so that they always remain within a given half optical cycle of the field, where they constantly gain energy until they leave the focal volume. 1D Analytical calculations [3] show that for relativistic electrons, the maximum energy gain from this process is ∆E ∝ mc 2 γ 0 a 2 0 , where γ 0 is the electron initial Lorentz factor, and a 0 is the normalized laser vector potential, m the electron mass, and c the vacuum light velocity. Reaching high energy gains thus requires high initial energies γ 0 1 and/or ultrahigh laser amplitudes (a 0 1).In contrast with the large body of theoretical work published on this vacuum laser acceleration (VLA) of electrons to relativistic energies, experimental observations have largely remained elusive [12][13][14][15][16][17] -sometimes even controversial [18,19]-and have so far not demonstrated significant energy gains. This is because VLA occurs efficiently only for electrons injected in t...

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“…It is therefore essential that the efficiency measurement is accompanied by a simultaneous determination of the beam divergence. In the past, a number of efficiency measurements mainly for individual harmonics and for different spectral ranges have been reported [13,18,21,[24][25][26]. The solid angle of the emission in these reports was mostly estimated without concurrent determination of the actual emission cone.…”

Section: Introductionmentioning

confidence: 99%