Welcome to attosecond, strong-field physics

Jean Marcel Ngoko Djiokap
Jean Marcel Ngoko Djiokap
Associate Professor, AMOP
Department of Physics and Astronomy
(402) 472-5094
JH 310S
Ph.D. Université catholique de Louvain, Louvain-la-neuve, Belgium, 2010

Atomic Molecular and Optical Physics

Professor Ngoko Djiokap is carrying out research in the fields of theoretical atomic and molecular physics with a focus on intense laser interactions with atoms and molecules, attosecond physics, and ultrafast highly-correlated processes involving attosecond laser pulses and electron impact.

Professor Ngoko Djiokap's expertise is on developing both ab initio numerical and analytical tools to uncover and predict new phenomena, and to analyze experimental results.

Ngoko Djiokap Research Group



Left: Dr. Dian Peng (Postdoc)


Middle: J.M. Ngoko Djiokap (Principal Investigator)


Right: Dr. Hua-Chieh Shao (Postdoc).


Somewhere in the Background: Nathaniel Strandquist (Graduate Student).


Research Highlights


Study details final breakthroughs of late Nebraska physicist


An internationally renowned career that began in New York City and Chicago and London before taking him, finally and for good, to Lincoln, would end on the sixth floor of the Bryan Medical Center’s East Campus.

Read more about their study in the UNL Today article.


Diagrams of theoretical prediction and experimental demonstration of Electron Matter-Wave Vortices

Experimental Confirmation of Electron Matter-Wave Vortices

Bottom: Theoretical Prediction

  • Multi-(two) photon Ionization of Helium Atom
  • Pair of time-delayed, counterrotating circularly-polarized pulses
  • Attosecond laser pulses
  • Photoelectron momentum distribution in the polarization plane
  • Four-armed spiral vortex patterns
  • J.M. Ngoko Djiokap et al., Phys. Rev. A 94, 013408 (2016)

Top: Experimental Demonstration

  • Multi-(three) photon Ionization of Potassium Atom
  • Pair of time-delayed, counterrotating circularly-polarized pulses
  • Femtocond laser pulses
  • Photoelectron momentum distribution in the polarization plane
  • Six-armed spiral vortex patterns
  • Pengel et al., Phys. Rev. Lett. 118, 053003 (2017)

09/11/2015 cover Phys Rev Lett

A Dramatic example of wave-particle duality

Interference between photoelectron wave packets (in momentum space) produced in the ionization of a helium atom by a pair of oppositely circularly polarized attosecond laser pulses that are time delayed.

The produced two-start spiral vortex patterns have a counterpart in optics, providing thus a dramatic example of wave-particle duality.

More information can be found on https://journals.aps.org/prl/issues/115/11

 Marcel (left) and Tony (right): PRL 2015
Physicists discover spiral vortex patterns from electron waves

University of Nebraska-Lincoln physicists have made a compelling discovery that graces the Sept. 11 cover of the journal Physical Review Letters. In their new study, physicists Anthony Starace and Jean Marcel Ngoko Djiokap report an unusual pattern of wave interference produced when an electron is ejected, or ionized, from its orbit around a helium atom.

Read more about their study in the UNL Today article.


 Nature Physics Highlights: PRL 2015

Attosecond Pulses Vortex Mixer

Research highlighted by Nature Physics, written by Editor Iulia Georgescu.

This article can be retrieved on Nature Physics 11, 800 (2015).
 Marcel (left) and Tony (right): PRL 2014

Study details laser pulse impacts on behavior of electrons

By solving a six-dimensional equation that had previously stymied researchers, UNL physicists have pinpointed the characteristics of a laser pulse that yields electron behavior they can predict and essentially control.

More information can be found on UNL Today.
 New Journal of Physics Highlights

Enhanced asymmetry in few-cycle attosecond pulse

ionization of He in the vicinity of autoionizing

Research highlighted in a special issue of New Journal of Physics, written Editorially by D. Bauer et al.

Highly correlated effects in attosecond pulse single ionization of helium were predicted numerically by solving the corresponding two-electron time-dependent Schroedinger equation in the presence of an intense, linearly-polarized, few-cycle, extreme ultraviolet laser pulse.

More information can be found on New Journal of Physics 14 (2012) 095010.