High-order harmonic generation in Xe, Kr, and Ar driven by a 2.1-μm source: High-order harmonic spectroscopy under macroscopic effects

摘要

We experimentally and numerically study the atomic response and pulse propagation effects of high-ordernharmonics generated in Xe, Kr, and Ar driven by a 2.1-μm infrared femtosecond light source. The light source isnan optical parametric chirped-pulse amplifier, and a modified strong-field approximation and three-dimensionalnpulse propagation code are used for the numerical simulations. The extended cutoff in the long-wavelength-drivennhigh-order harmonic generation has revealed the spectral shaping of high-order harmonics due to the atomicnstructure (or photorecombination cross section) and the macroscopic effects, which are the main factors ofndetermining the conversion efficiency besides the driving wavelength. Using precise numerical simulations tondetermine the macroscopic electron wave packet, we are able to extract the photorecombination cross sectionsnfrom experimental high-order harmonic spectra in the presence of macroscopic effects. We have experimentallynobserved that the macroscopic effects shift the observed Cooper minimum of Kr from 80 eV to 60–70 eV andnwash out the Cooper minimum of Ar. Measured high-harmonic conversion efficiencies per harmonic near thencutoff are ∼10−9 for all three gases.