Electronic structure in atoms and molecules modulates the amplitude and phase of high harmonic generation (HHG). We report measurements of the high harmonic spectral amplitude and phase in N2. The phase is measured interferometrically by beating the N2 harmonics with those of an Ar reference oscillator in a gas mixture. A rapid phase shift of 0.2π is observed in the vicinity of the HHG spectral...

We report theoretical calculations of high-order harmonic generation (HHG) by intense infrared lasers in atomic and molecular targets taking into account the macroscopic propagation of both fundamental and harmonic fields. On the examples of Ar and N2, we demonstrate that these ab initio calculations are capable of accurately reproducing available experimental results with isotropic and aligned...

High harmonic generation (HHG) enables the production of coherent light in the extreme-ultraviolet (XUV) spectral region. However, the radiation conversion efficiency from infrared to the XUV is low. We observed enhancement of HHG in gas mixtures ofH2 and Ne compared to pure gasesH2 or Ne. Our experiments show that at an intensity of ∼1.5 × 1014 W∕cm2 and in mixtures of gases with significantly...

High-order harmonic generation (HHG) in gases has been established as an important technique for the generation of coherent extreme ultraviolet (XUV) pulses at ultrashort time scales. Its main drawback, however, is the low conversion efficiency, setting limits for many applications, such as ultrafast coherent imaging, nonlinear processes in the XUV range, or seeded free electron lasers. Here we...

We report theoretical calculations of the effect of the multiple-orbital contribution in high-order harmonic generation (HHG) of aligned CO2 with the inclusion of macroscopic propagation of harmonic fields in the medium. Our results show very good agreement with recent experiments for the dynamics of the minimum in HHG spectra as laser intensity or alignment angle changes. Calculations are carr...

High harmonic generation (HHG) provides a laboratory scale source of coherent radiation ideally suited to lensless coherent diffractive imaging (CDI) in the EUV and X-ray spectral region. Here we demonstrate transmission EUV ptychography, a scanning variant of CDI, using radiation at a wavelength around 29 nm from an HHG source. Image resolution is diffraction-limited at 54 nm, and fields of vi...

The three-step model (TSM) of high-harmonic generation (HHG) is generalized to atomic and molecular many-electron systems. Using many-body perturbation theory, corrections to the standard TSM due to exchange and electron-electron correlations are derived. It is shown that canonical Hartree-Fock orbitals represent the most appropriate set of one-electron states for calculating the HHG spectrum. ...

We analyse the theory of single photoionization (PI) and high-order harmonic generation (HHG) by intense lasers from aligned molecules. We show that molecular-frame photoelectron angular distributions can be extracted from these measurements. We also show that, under favourable conditions, the phase of PI transition dipole matrix elements can be extracted from the HHG spectra. Furthermore, by v...

High harmonic generation (HHG) provides a flexible framework for the development of coherent light sources in the extreme-ultraviolet and soft x-ray regimes. However it suffers from low conversion efficiencies as the control of the HHG spectral and temporal characteristics requires manipulating electron trajectories on attosecond time scale. The phase matching mechanism has been employed to sel...

Plasmonic high-harmonic generation (HHG) drew attention as a means of producing coherent extreme ultraviolet (EUV) radiation by taking advantage of field enhancement occurring in metallic nanostructures. Here a metal-sapphire nanostructure is devised to provide a solid tip as the HHG emitter, replacing commonly used gaseous atoms. The fabricated solid tip is made of monocrystalline sapphire sur...