The quantitative rescattering theory (QRS) for high-order harmonic generation (HHG) by intense laser pulses is presented. According to the QRS, HHG spectra can be expressed as a product of a returning electron wave packet and the photorecombination differential cross section of the laser-free continuum electron back to the initial bound state. We show that the shape of the returning electron wave packet is determined mostly by the laser. The returning electron wave packets can be obtained from the strong-field approximation or from the solution of the time-dependent Schrödinger equation (TDSE) for a reference atom. The validity of the QRS is carefully examined by checking against accurate results for both harmonic magnitude and phase from the solution of the TDSE for atomic targets within the single active electron approximation. Combining with accurate transition dipoles obtained from state-of-the-art molecular photoionization calculations, we further show that available experimental measurements for HHG from partially aligned molecules can be explained by the QRS. Our results show that quantitative description of the HHG from aligned molecules has become possible. Since infrared lasers of pulse durations of a few femtoseconds are easily available in the laboratory, they may be used for dynamic imaging of a transient molecule with femtosecond temporal resolutions.



Keywords and Phrases

Aligned Molecules; Atomic Targets; Bound State; Continuum Electrons; Differential Cross Section; Dinger Equation; Dynamic Imaging; Electron Wave Packet; Experimental Measurements; Femtoseconds; Harmonic Magnitudes; High Order Harmonic Generation; Infrared Laser; Intense Laser Pulse; Molecular Photoionization; Photorecombination; Pulse Durations; Quantitative Description; Rescattering; Single Active Electron Approximations; Strong-Field Approximations; Temporal Resolution; Time-Dependent; Transient Molecules; Transition Dipole, Atoms; Electron Transport Properties; Harmonic Analysis; Harmonic Generation; Molecules; Pulsed Laser Applications; Wave Packets; Waves, Laser Theory

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