Table of contents

High-order-harmonic generation (HHG) for the H₂⁺ molecule in a 3-fs, 800-nm few-cycle Gaussian laser pulse is investigated by solving the time-dependent Schrödinger equation. The spatial distribution on HHG is demonstrated and the results present the recombination process of the electron with the two nuclei. And there is little possibility of the recombination of the electron with the nuclei around the origin z = 0 a.u. and equilibrium internuclear positions z = ±1.3 a.u.. The electron-nuclear wave packet and ionization probability are investigated to explain the physical mechanism.

We calculate the low-order harmonic generation (LOHG) by solving three-dimensional time-dependent Schrödinger equation with an accurate model potential of helium (He) atom in an intense laser fields. The satellite-peak structures of the LOHG are obtained in the harmonic spectra of He atom. We analyze the emission properties of the LOHG by employing a synchrosqueezing transform technique. Our results show that the satellite-peak structures contain the information of the bound states and the Stark shift of He atom in an intense laser fields.

We present gauge-invariant reformulation of time-dependent configuration interaction singles (TDCIS) method and its applications to high-harmonic generation (HHG) from three-dimensional atoms. The conventional TDCIS method suffers from a violation of gauge-invariance, which prevents efficient simulations of high-field phenomena within the velocity gauge. In our reformulation, rotated velocity gauge transformed from the length gauge is employed instead of the velocity gauge. We simulate HHG from atoms and show gauge-invariance and performance of our rotated velocity gauge.

We present an ab initio quantum study of below-threshold harmonic generation (BTHG) from H₂⁺ molecules in the presence of an intense laser field by solving the time-dependent Schrödinger equation accurately in space and time. We find that multiple channels contribute to BTHG of H₂⁺ molecules, which are related to the electron driven initially at specific time of the laser pulse from one nuclear core to another nuclear core or back to the parent core itself. The distinct contributions of these channels are distinguished by using a novel synchro squeezing time-frequency analysis.

We show that a novel carrier-wave population transfer, i.e., interband excitations are confined to an extremely short time window due to their coupling to the intraband motion, is responsible for the enhancement of the interband HHG and the anomalous carrier-envelope phase dependence observed in recent experiments on semiconductors. The results give the answers of how inter- and intraband dynamics are coupled together and why the interband polarization can dominate the HHG emission in many semiconductors which is a highly debated topic in the community.

We numerical and analytically investigate the electron dynamics of high-order harmonic generation (HHG) in solids driven by strong mid-infrared few-cycle laser pulses. Our numerical model distinguishes contributions to the HH yield from (i) intra- and interband transitions and (ii) the central Γ–point of the first Brillouin zone (BZ) versus the entire first BZ of the initial valence band.

We have developed an ab-initio multi-scale simulation to model light synthesis and propagation through transparent media accounting for the non-linear response of the solid. Using this approach we are able to investigate the build-up of high harmonics induced by strong and short laser pulses along the propagation direction inside a large band-gap dielectric, diamond. Detailed analysis of the results allows to identify minimum requirements necessary to realistically model laser-solid interactions.

We have observed the autoionization of the laser-coupled 2s2p¹P^o and 2p²¹S^e resonances in helium. The ions were collected while varying the frequency and delay of the extreme-ultraviolet (EUV) excitation pulse with respect to the linearly chirped visible (VIS) laser pulse. From the measured frequency-delay map the Autler-Townes splitting, the EUV-VIS cross-correlation and the linear chirp parameter were extracted.

We present a high-energy mid-infrared optical parametric amplifier source tunable between 2.8 and 3.8 μm for strong-field applications. We exploited this source in combination with a 800 nm source for generating high-order harmonics in atoms and molecules in a two-color pulse scheme.