Lab Director: Tom Morgan
Graduate Students: Jonathan Lambert,
Pennan Chinnasamy and
Ramesh Marhatta
Undergraduate Students: Jace Haested '10
German Exchange Student: Michael Jag (University of Tubingen)
Recent Graduates: Jack DiSciacca '07 (presently in physics graduate schoolTo see some recent work in progress click here.
RECURRENCE SPECTROSCOPY OF RYDBERG ATOMS AND MOLECULES
IN ELECTRIC FIELDS
Supported by the National Science Foundation
Project Summary
Morgan
An experimental and computational research program is active in the investigation of Rydberg atoms and molecules in electric fields. Tunable, pulsed, laser light, either UV single photon or two color visible, excites a 4 keV metastable atom beam, prepared by collisions in a metal vapor cell, to Rydberg Stark states that are detected either at the location of excitation or downstream from it. Data recording is done using scaled variables, which utilizes the simultaneous variation of the laser energy and the external electric field, with the functional dependence of these quantities determined from intrinsic scaling properties of the classical Hamiltonian. The resulting complex quantum spectrum, when Fourier transformed, reveals a finite number of peaks called recurrences, corresponding to electron trajectories that follow closed classical orbits that travel far from the nucleus and return. The power of this experimental technique, referred to as recurrence spectroscopy, is that it provides an alternative way of interpreting quantum spectra, yielding insight into Rydberg state dynamics.
Quantum mechanical atomic wavefunctions do not provide the means to easily visualize the dynamics of the atom, whereas recurrence spectroscopy, combined with semiclassical theory, provides a physical understanding of the motion of the Rydberg electron through its classical orbits. The experiments permit a semi-classical parameterization of photoabsorption, which leads to a way to examine Rydberg Stark states in terms of classical closed orbits. Initial studies at Wesleyan have resulted in the observation and interpretation of recurrences in the fundamental two-electron helium atom in an electric field. Extensions of this work have permitted the measurement of recurrences in argon, a larger, more complex, multi-channel atom, revealing intriguing new effects in the spectrum. We have also completed a computational study of recurrences in atomic double Rydberg states, demonstrating that a simple classical approach can serve to characterize doubly excited asymmetric states. We are now exploring the consequences of additional quantum mechanical degrees of freedom by studying simple molecules.
We have made recurrence measurments in molecular hydrogen and are presently extending these studies
The program is aimed at answering fundamental questions about the behavior of Rydberg atoms and molecules in external fields, and their quantum - classical correspondence, particularly when the classical system is chaotic. Remarkably, quantum statistical mechanics can derive classical dynamics, and so too should there exist a link between quantum behavior and classical chaos. A major goal of our research is to help uncover this connection.
This project unifies laser technology with particle accelerator technology to produce a sophisticated spectrometer for precision studies of high energy atomic and molecular states. The preparation of these states involves two steps; the first stage utilizes a collision process to prepare a metastable state of an atom or molecule in a fast beam. In the second stage a laser beam overlaps the fast beam coaxially and results in a transition from the metastable state to a higher energy state. Helium states up to principle quantum number 100 have been laser excited in vacuum and in the presence of a uniform electric field from the collisionally-prepared 2 S state and detected using electric field ionization. Using this experimental approach, work is under way to study quantum chaos. The excited helium atom in an electric field provides a simple two electron system for investigating how classical and quantum mechanics are connected in a chaotic regime.
However, we will not be put off by complexity - neither conceptual, computational nor experimental. We have made measurements on atomic systems with more complex cores, like argon and xenon. We are presently doing experiments with molecules.
A collaberation is under way with the Queen's University of Belfast, N. Ireland to study the role and importance of excited atoms and molecules in plasmas
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