摘要
We report evidence for the first generation of XUV spectra from relativistic surface high-harmonic generation(SHHG)on plasma mirrors at a kilohertz repetition rate,emitted simultaneously with energetic electrons.SHHG spectra and electron angular distributions are measured as a function of the experimentally controlled plasma density gradient scale length Lg for three increasingly short and intense driving pulses:24 fs and a0=1:1,8 fs and a0=1:6,and finally 4 fs and a0≈2:1,where a0 is the peak vector potential normalized by mec/e with the elementary charge e,the electron rest mass me,and the vacuum light velocity c.For all driver pulses,we observe correlated relativistic SHHG and electron emission in the range Lg∈½λ/20,λ/4,with an optimum gradient scale length of Lg≈λ/10.This universal optimal Lg-range is rationalized by deriving a direct intensity-independent link between the scale length Lg and an effective similarity parameter for relativistic laser-plasma interactions.
基金
supported by the Agence Nationale pour la Recherche(ANR-11-EQPX-005-ATTOLAB and ANR-14-CE32-0011-03 APERO)
Investissements d’Avenir Program LabEx PALM(ANR-10-LABX-0039-PALM)
European Research Council(ERC FEMTOELEC 306708 and ERC ExCoMet 694596)
Laserlab-Europe(H2020-EU.1.4.1.2.grant agreement ID 654148)
Région Ile-de-France(SESAME 2012-ATTOLITE).
