My name is Jens Svensmark and I’m an Assistant Professor specializing in Molecular Physics

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Assistant Professor

The University of Electro-Communications

Nov 2019 – Present Tokyo


The University of Electro-Communications

Nov 2017 – Nov 2019 Tokyo


Kansas State University

Nov 2016 – Oct 2017 Kansas

Recent & Upcoming Talks

Within strong field physics a lot of attention has lately been directed towards producing long wavelength laser pulses in the mid-infrared and terahertz regimes, which could make it possible to measure molecular dynamics in detail. However, most theoretical methods fail in these regimes, due to the large dynamic range of spatial separations and energies involved. The adiabatic theory of ionization [Phys. Rev. A 86, 043417 (2012)] exploits the fact that the field varies slowly for such pulses, and it therefore excels in providing accurate descriptions of the laser-molecule interactions. We will present a recently developed version of this adiabatic theory (AAnf) that is applicable to molecules [Phys. Rev. A 101, 053422 (2019)], and treats nuclear motion in addition to all interactions among nuclei, electrons and the laser field. First, we will demonstrate that the theory is accurate by comparing to exact numerical solutions of the time-dependent Schrödinger equation (TDSE) in absolute scale, see Figure~1. Next, we will show examples of applications of this theory to problems in strong-field physics. For instance, the theory can be used to examine the effect of using different isotopes on observables. Finally, we will also present preliminary results for processes in which an ionized electron rescatters on the molecular ion, including inelastic scattering channels.

The adiabatic theory of tunneling ionization has been successfully used to describe tunneling ionization of atoms [Phys. Rev. A 86, 043417 (2012)]. This theory works particularly well for describing systems in strong, slowly oscillating laser fields in the near and far-infrared parts of the spectrum; a regime of laser parameters that are currently receiving a lot of attention within strong field physics. In this work we seek to apply the adiabatic theory to molecular systems, while treating both nuclear and electronic degrees of freedom. We propose a theory that combines adiabatic theory with a variation of the well known Born-Oppenheimer approximation. The results of this theory is compared to accurate TDSE calculations.

Recent Publications

Some publications i have recently published

The adiabatic theory of strong-field ionization of molecules with internuclear motion included into consideration is developed. Two adiabatic regimes in terms of the electronic, nuclear, and laser field timescales are considered. In the first regime, field is the slowest; that is, its timescale is much larger than the electronic and nuclear timescales. The corresponding theory generalizes the adiabatic theory of strong-field ionization of atoms and molecules with frozen nuclei [Phys. Rev. A 86, 043417 (2012)] by treating the internuclear motion on equal footing with the electronic motion. In the second regime, the active electron is the fastest; that is, its timescale is much smaller than that of the nuclei and laser field. The corresponding theory naturally involves the Born-Oppenheimer approximation. The two versions of the adiabatic theory are validated by comparing their predictions with accurate numerical results obtained by solving the time-dependent Schrödinger equation (TDSE) for a model diatomic molecule with one electronic and one internuclear degree of freedom. The adiabatic results are shown to converge to the TDSE results uniformly with respect to the laser field amplitude both in tunneling and over-the-barrier ionization regimes. Two applications of the theory to the analysis of strong-field effects associated with the internuclear motion are discussed.

We present the theory of tunneling ionization of molecules with both electronic and nuclear motion treated quantum mechanically. The theory provides partial rates for ionization into the different final states of the molecular ion, including both bound vibrational and dissociative channels. The exact results obtained for a one-dimensional model of H2 and D2 are compared with two approximate approaches, the weak-field asymptotic theory and the Born-Oppenheimer approximation. The validity ranges and compatibility of the approaches are identified formally and illustrated by the calculations. The results quantify that at typical field strengths considered in strong-field physics, it is several orders of magnitude more likely to ionize into bound vibrational ionic channels than into the dissociative channel.

In this dissertation the theory of tunneling ionization of molecules is presented and the results of numerical calculations are shown.

We present a theoretical study of the dissociative tunneling ionization process. Analytic expressions for the nuclear kinetic energy distribution of the ionization rates are derived. A particularly simple expression for the spectrum is found by using the Born-Oppenheimer (BO) approximation in conjunction with the reflection principle. These spectra are compared to exact non-BO ab initio spectra obtained through model calculations with a quantum mechanical treatment of both the electronic and nuclear degrees of freedom. In the regime where the BO approximation is applicable, imaging of the BO nuclear wave function is demonstrated to be possible through reverse use of the reflection principle, when accounting appropriately for the electronic ionization rate. A qualitative difference between the exact and BO wave functions in the asymptotic region of large electronic distances is shown. Additionally, the behavior of the wave function across the turning line is seen to be reminiscent of light refraction. For weak fields, where the BO approximation does not apply, the weak-field asymptotic theory describes the spectrum accurately.

We study tunneling ionization in a one-dimensional three-body model of a molecule, treating both electronic and nuclear degrees of freedom exactly. In a recent paper [Phys. Rev. Lett. 111, 153003 (2013)] it was demonstrated using a finite-range potential that the Born-Oppenheimer approximation breaks down for fields weaker than a critical field FBO when describing tunneling ionization of molecules, but works for stronger fields. It was also demonstrated that the weak-field asymptotic theory allows for an accurate description in this weak-field limit. In the present paper, we consider a potential with a Coulomb tail and nonzero dipole moment, modeling polar molecules. Our study shows that the conclusions of the aforementioned paper also hold for this potential.


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