Dynamic Two-Center Interference in High-Order Harmonic Generation from Molecules with Attosecond Nuclear Motion

Abstract

Abstract:We report a new dynamic two-centre interference effect in High-HarmonicGeneration from H 2 , in which the attosecond nuclear motion of H 2 + initiated at ionisation causes interference to be observed at lower harmonic orders than would be the case for static nuclei. To enable this measurement we utilise a recently developed technique for probing the attosecond nuclear dynamics of small molecules. The experimental results are reproduced by a theoretical analysis based upon the strong field approximation which incorporates the temporally dependent two-centre interference term.High-harmonic generation (HHG) has proven to be a rich area of study over the last decade, finding application in a number of fields of laser science, such as coherent X-ray production [1,2] , attosecond pulse generation [3][4][5], and time resolved probing of nuclear dynamics [6,7]. HHG has also led to important advances towards the goal of structural imaging of small molecules [8][9][10][11][12][13][14][15], the harmonic emission depending strongly on the nature of the molecular orbital involved. This is seen most clearly within the Strong Field Approximation (SFA), in which the amplitude for HHG is determined by the Fourier transform of the bound state wavefunction.The wavefunctions relevant to HHG are those describing the propagated continuum electron ( c ψ ), and the bound electronic state from which the electron was ionised ( g ψ ). Recollision of the electron wavepacket with its parent ion results in a high local electron density (described by

Time-dependent density-functional-theory calculation of high-order-harmonic generation of H2

“…1) and τ (ω) is the recollision time. This approximation has the advantage that it applies to the contribution from the short trajectories [16], matching the conditions of the available experimental data [4,5]. We thus make a relatively simple SFA model, in which we take the amplitude as R independent and obtain the R dependence of the phase using Eq.…”

“…In recent years HHG of molecules has been studied for its potential to probe, with subfemtosecond temporal resolution, nuclear dynamics including vibration [3][4][5][6][7] and dissociation [7]. The foundation of these applications is the sensitivity of HHG emission to the nuclear geometry and motion.…”

“…The foundation of these applications is the sensitivity of HHG emission to the nuclear geometry and motion. So far, the involvement of multiple molecular orbitals [6,7] and two-center interference [5,7] have been proposed as causes for the large oscillation of the HHG intensity in response to geometry changes in molecules. Further theoretical studies that detail the relation of molecular structure and dynamics with their HHG can contribute to the maturity of the application of HHG as a subfemtosecond molecular dynamics probe.…”

“…In a 2008 follow-up experiment, Baker et al [5] remeasured the isotope effect with different laser intensities and a longer pulse duration. They demonstrated that this model had to be extended by postulating a dynamic two-center interference effect, which is R dependent.…”

Role of resonance-enhanced multiphoton excitation in high-harmonic generation of N2: A time-dependent density-functional-theory study

“…Exciting results have been obtained in recent years by using high-harmonic generation (HHG) [1,2] to probe molecular dynamics with subfemtosecond temporal resolution [3][4][5][6][7][8]. The sensitivity of HHG emission to molecular geometry and motion is the foundation for this application.…”