Abstract: 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.
Abstract: Attosecondattosecond science; extreme ultraviolet; high-order harmonic generation; Ramsey-type spectroscopy Optical and Ramsey-Type Interferometry by Postgeneration Splitting of Harmonic PulseTime domain Ramsey-type interferometry is useful for investigating spectroscopic information of quantum states in atoms and molecules. The energy range of the quantum states to be observed with this scheme has now reached more than 20 eV by resolving the interference fringes with a period of a few hundred attoseconds. This attosecond Ramsey-type interferometry requires the irradiation of a coherent pair of extreme ultraviolet (XUV) light pulses, while all the methods used to deliver the coherent XUV pulse pair until now have relied on the division of the source of an XUV pulse in two before the generation. In this paper, we report on a novel technique to perform attosecond Ramsey-type interferometry by splitting an XUV high-order harmonic (HH) pulse of a sub-20 fs laser pulse after its generation. By virtue of the postgeneration splitting of the HH pulse, we demonstrated that the optical interference emerging at the complete temporal overlap of the HH pulse pair seamlessly continued to the Ramsey-type electronic interference in a helium atom. This technique is applicable for studying the femtosecond dephasing dynamics of electronic wavepackets and exploring the ultrafast evolution of a cationic system entangled with an ionized electron with sub-20 fs resolution.
Abstract: Here, we report the recent progress on the front end developed for the 100 PW-class laser facility. Using 3 stages of optical parametric chirped-pulse amplification (OPCPA) based on lithium triborate (LBO) crystals, we realized a 5.26 J/0.1 Hz amplified output with a bandwidth over 200 nm near the center wavelength of 925 nm. After the compressor, we obtained a pulse duration of 13.4 fs. As the compression efficiency reached 67%, this OPCPA front end could potentially support a peak power of 263 TW at a repetition rate of 0.1 Hz. To the best of our knowledge, among all the 100 TW-level OPCPA systems, it shows the widest spectral width, the shortest pulse duration, and it is also the first OPCPA system working at a repetition-rate mode.