Ponderomotive shifts induced by intense laser-driven coherent extreme ultraviolet radiation

Abstract

Signatures of strong-field effects induced by an intense attosecond pulse train, synthesized by the superposition of a Ti:sapphire laser high-order harmonics are observed in atomic two-photon ionization. Ponderomotive shifts in the photoelectrons' kinetic energies have been measured in the non-resonant two-photon ionization of Helium atoms induced by the interaction with extreme ultraviolet radiation at intensities on the order of 10 15 W cm −2 . These results inaugurate the topic of strong-field phenomena in experimental laser based attosecond science.

Quantum Optical Aspects of High-Harmonic Generation

“…(For example, at the density n e = 10 18 /cm 3 , the plasmon energy is ω p = 0.035 eV, which is only slightly larger than two percent of the photon energy 1.5 eV. Then ω 2 p /2ω 2 = 2 × 10 −4 , i.e., ∆ω = 2 × 10 −4 ω, and this means n × (3 × 10 −4 eV) "blue-shift" of the n-th harmonics [114][115][116]. The remaining linear, off-diagonal term in (A41) can be transformed out by using the a displacement properties, shown in Equation (A7),…”

“…) shows the dispersion relation of plasmons, propagating in an underdense plasma. For example, at the density only slightly larger than two percent of the photon energy 1.shift" of the  n th harmonics[115][116][117]. The remaining linear, off-diagonal term in (A41) can be transformed out by using the a displacement properties, shown in Equation (A7),…”