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Rydberg Atoms in Strong Fields

(wikipedia link to Rydberg atoms)

For many years, we have had a strong effort in studying highly excited atoms and molecules. The interest in this area is that highly excited atoms can be understood using classical and quantum ideas. We are particularly interested in the behavior of these atoms in strong fields. The fields break the spherical symmetry of the atom and give rise to an interesting interplay between different types of motion. Also, specific and well controlled experiments can be performed on these systems.



For these calculations, we often solve both the classical equations of motion and the time dependent Schrodinger equation which governs the quantum behavior. Depending on the system being studied, the quantum calculations solve for the wavefunction can be converged for distances out to 10-6 m from the ion and include angular momentum up to 1000 hbar. Below is a brief description of results in two recent publications.



A.S. Stodolna, F. Lepine, T. Bergeman, F. Robicheaux, A. Gijsbertsen, J.H. Jungmann, C. Bordas, and M.J.J. Vrakking, "Visualizing the coupling between red and blue Stark states using photoionization microscopy," Phys. Rev. Lett. 113, 103002 (2014). PDF (1210 kB)

This paper is a collaboration between experiment and theory to coupling between different types of states of atoms in electric fields. Electric fields can mix the angular momentum of a weakly bound electron giving states with qualitatively different character. Some have very large dipole moments aligned with the electric field and some are anti-aligned. For some states, small changes in electric field strength can cause states with qualitatively different character to have similar energy. Since states with nearly the same energy can be mixed by small perturbations, the small region occupied by the core electrons can lead to nearly complete mixing between the states.



This image is a schematic of how the experiment works. The electron is excited to the region near these states and can be pulled from the atom by the electric field. The transverse part of the electron wave can be imaged and gives a set of concentric rings. The intensity and radii of the rings reflect the state of the electron when it leaves the atom.



This image is a figure from the paper showing how the rings evolve over a very small range of energy. The different character of the rings reflect the different character of the states on the atom.

We used similar techniques were used to study H atoms: A.S. Stodolna, A. Rouzee, F. Lepine, S. Cohen, F. Robicheaux, A. Gijsbertsen, J.H. Jungman, C. Bordas, and M.J.J. Vrakking, "Hydrogen atoms under magnification: direct observation of the nodal structure of Stark states," Phys. Rev. Lett. 110, 213001 (2013). PDF (1,150 kB) Physics Focus (viewpoint)



Changchun Zhong and F. Robicheaux, "Spectrum of quasistable states in a strong infrared field," Phys. Rev. A 92, 013406 (2015). PDF (642 kB)

Inspired by experiments from Tom Gallagher's group, this paper reported results from calculations that studied the states of quasistable atoms in strong IR fields. The atom is excited to near the threshold region while a strong IR field is on. At most excitation energies, the IR will give energy to the weakly bound electron and quickly ionize. However, at some specific energies, the atom is strangely stable.



This image shows a schematic of the situation. The left graph shows the intensity of the UV laser and the strong IR as a function of time. The right graph shows the effect of photon-absorption and emission on the electron energy with the red arrow representing the UV photon and the blue arrows representing the IR photons.



This image shows the calculated probability for the electron to survive on the atom to the end of the IR pulse as a function of the initial electron energy. The different color curves are for different IR strengths. The peaks are typically separated by the energy of an IR photon. The right graph has bending lines that show all of the peaks shift with the ponderomotive energy of the electron.



This image shows shows the distribution of final states after the IR is turned off for four different IR intensities. For all of the high intensity cases, the electron is most likely to be found in very weakly bound states of high principal quantum. This system displays a well known effect that very weakly bound electrons can be less easily ionized in an oscillating field than the strongly bound electrons.



Five Recent Publications

Changchun Zhong and F. Robicheaux, "Spectrum of quasistable states in a strong infrared field," Phys. Rev. A 92, 013406 (2015). PDF (642 kB)

B.C. Yang and F. Robicheaux, "Field-ionization of Rydberg atoms in a single-cycle pulse," Phys. Rev. A 91, 043407 (2015). PDF (296 kB)

A.S. Stodolna, F. Lepine, T. Bergeman, F. Robicheaux, A. Gijsbertsen, J.H. Jungmann, C. Bordas, and M.J.J. Vrakking, "Visualizing the coupling between red and blue Stark states using photoionization microscopy," Phys. Rev. Lett. 113, 103002 (2014). PDF (1210 kB)

G.W. Gordon and F. Robicheaux, "A classical analogue for adiabatic Stark splitting in non-hydrogenic atoms," J. Phys. B 46, 235003 (2013). PDF (1450 kB)

A.S. Stodolna, A. Rouzee, F. Lepine, S. Cohen, F. Robicheaux, A. Gijsbertsen, J.H. Jungman, C. Bordas, and M.J.J. Vrakking, "Hydrogen atoms under magnification: direct observation of the nodal structure of Stark states," Phys. Rev. Lett. 110, 213001 (2013). PDF (1,150 kB) Physics Focus (viewpoint)

Francis Image

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