Continuous pump-probe experiment to observe Zeeman wave-packet dynamics
ORAL
Abstract
Time-resolved laser spectroscopy, combined with high-resolution momentum imaging, provides insights into atomic and molecular dynamics. We present a novel tool based on cold target recoil ion momentum spectroscopy (COLTRIMS) for time-resolved photoelectron spectroscopy, designed to study slow nanosecond atomic dynamics. Unlike conventional pump-probe methods, which rely on scanning the delays between two pulses, we use a femtosecond pump pulse and a weak continuous-wave (CW) probe, which can ionize the excited atoms at any time after the pump. Typically, COLTRIMS requires time-of-flight data referenced to a pulsed source. This experiment, however, recovers time information by exploiting the particles’ motion in the spectrometer fields and the fact that the momenta of the target fragments sum to zero.
Specifically, an All Optical Trap (AOT) is used to prepare a target of atomic 6Li. The atoms are excited into a Rydberg wave packet using a femtosecond light source, tuned to emit pulses with a central wavelength of 735 ± 10 nm, a pulse width of 50 fs, and a repetition rate of 200 kHz. After excitation, the atoms spontaneously decay toward the ground state. An Optical Dipole Trap (ODT) emitting continuous-wave infrared laser light at 1070 ± 5 nm is employed to ionize the excited atoms. Since direct time information about ionization in the CW field is not accessible, an algorithm [1] is used to numerically calculate the ionization time from the relative positions of recoil ions and electrons on their respective particle detectors. The ionization rate is then plotted as a function of photo-electron energy and the derived ionization time. The ionization rate shows a periodic time dependence with two dominant streaks: one at about 0.9 eV, corresponding to electrons from the Rydberg states, and the other at about 0.3 eV, resulting from photoionization following spontaneous decay to the n = 4 state. A simple model [2] incorporating Zeeman and Autler-Townes effects has been developed to explain the observed periodic dynamics.
[1] Romans K. et. al. Review of Scientific Instruments 96, no. 12 (2025).
[2] Romans K. et al. Physical Review A 112, no. 3 (2025): 033102.
Specifically, an All Optical Trap (AOT) is used to prepare a target of atomic 6Li. The atoms are excited into a Rydberg wave packet using a femtosecond light source, tuned to emit pulses with a central wavelength of 735 ± 10 nm, a pulse width of 50 fs, and a repetition rate of 200 kHz. After excitation, the atoms spontaneously decay toward the ground state. An Optical Dipole Trap (ODT) emitting continuous-wave infrared laser light at 1070 ± 5 nm is employed to ionize the excited atoms. Since direct time information about ionization in the CW field is not accessible, an algorithm [1] is used to numerically calculate the ionization time from the relative positions of recoil ions and electrons on their respective particle detectors. The ionization rate is then plotted as a function of photo-electron energy and the derived ionization time. The ionization rate shows a periodic time dependence with two dominant streaks: one at about 0.9 eV, corresponding to electrons from the Rydberg states, and the other at about 0.3 eV, resulting from photoionization following spontaneous decay to the n = 4 state. A simple model [2] incorporating Zeeman and Autler-Townes effects has been developed to explain the observed periodic dynamics.
[1] Romans K. et. al. Review of Scientific Instruments 96, no. 12 (2025).
[2] Romans K. et al. Physical Review A 112, no. 3 (2025): 033102.
*The experimental material presented here is based on work supported by the U.S. National Science Foundation under Grant No. PHY-2207854.
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Publication: https://journals.aps.org/pra/pdf/10.1103/5fzd-g7qn
Presenters
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Shruti Majumdar
- Missouri University of Science & Technology