Atomic, Molecular & Optical Physics (AMO) Projects

Computational ultrafast dynamics for molecules (Theory)

Loren Greenman

E-mail: lgreenman@phys.ksu.edu

Number of REU participants: 1

The dynamics of molecules interacting with intense, ultrafast, or high-photon-energy laser fields pushes the frontier of complexity that can be described by current theories and computational techniques. However, it is precisely these regimes where we can learn new phenomena for molecules relevant to chemical reactivity and energy conversion. In this project, a 2019 REU student will explore new techniques for understanding molecular interactions on ultrafast timescales and complex dynamical processes.

Together, we will work with experimentalists at the James R. Macdonald Laboratory to understand complex processes by characterizing the potential energy of molecules at distorted geometries and in highly excited states. The student will learn to use state-of-the-art methods from the community of quantum chemistry, where quantum mechanics and applied mathematics are combined and applied to molecules. In the course of this project, we will use some of the most powerful supercomputers in the world including those at the National Energy Research Supercomputing Center (NERSC). Benefits include exposure to computer scripting in languages like Python, basic computer programming in Fortran or C++, and high-performance computational techniques.

Dissociation of molecular dication beams, such as CN²⁺ or CS₂ ²⁺, by
ultrafast intense laser pulses (Experiment)

Itzik Ben-Itzhak

E-mail: ibi@phys.ksu.edu

Number of REU participants: 1

During the 2021 REU program our research group will be involved in projects where undergraduate students can do interesting work and contribute to our research progress. Below I have briefly outlined a project which would best fit an REU student. We expect the project to provide hands-on experience in the laboratory, conducting advanced laser-matter interaction measurements, analyzing the data, and finally preparing the interpreted results for publication.
In addition, undergraduate students can get involved in other summer projects within our group [1]. Our research group currently includes my graduate students Naoki Iwamoto and Travis Severt (soon to become a post-doc) [2]. The REU student is expected to work closely with Travis, the other members of the group, and under the guidance of Dr. Kevin Carnes and myself.

We have been studying the interaction of intense ultrafast laser pulses with fast molecular ions through the application of a coincidence three-dimensional momentum imaging technique [3]. One important aspect of our experimental method is the ability to investigate unique molecular targets, such as the long-lived, vibrationally cold, CO²⁺ molecular ion, in the rapidly changing strong field of a laser [4]. We have recently extended the studies of metastable molecular ions [4] to other interesting long-lived molecular ions, namely NO²⁺ and CS²⁺, and found some intriguing phenomena. This summer, we plan to extend these studies and also move on to triatomic molecular ions, like OCS²⁺ and CS₂ ²⁺. These molecules open the door for three-body dissociation in addition to the two-body breakup we have studied thus far.

The REU project will involve generating the dications of interest in an ion source (for example, finding the best way to make CN²⁺), directing them to the crossing with the laser beam, then conducting a coincidence momentum imaging measurement of all fragments. Next, the student will spend time analyzing and interpreting the resulting data, planning and conducting new measurements as needed, and so on until the results are understood well enough to report them in a scientific publication. In short, the student will be exposed to most of the stages of the experimental investigation process.

1. It is important to note that the specific involvement of the REU student in any of the projects will depend on the qualifications and interests of the student as well as our needs at the time.
2. Former participant in the REU program of 2011.
3. See, for example, Bethany Jochim et al., J. Phys. Chem. Lett. 10, 2320 (2019), A.M. Sayler et al., J. Phys. B: At. Mol. Opt. Phys. 47, 031001 (2014), Nora G. Kling et al., Phys. Rev. Lett. 111, 163004 (2013), J. McKenna et al. New J. Phys. 14, 103029 (2012); Phys. Rev. Lett. 103, 103004 (2009); and Phys. Rev. Lett. 103, 103006 (2009).
4. J. McKenna et al., Phys. Rev. A 81, 061401(R) (2010).

Studying ultrafast molecular dynamics in pump-probe experiments with femtosecond lasers (Experiment)

Daniel Rolles and Artem Rudenko

E-mail: rolles@phys.ksu.edu or rudenko@phys.ksu.edu

Number of REU participants: 1

State-of-the-art femtosecond lasers can generate pulses with durations shorter than the time scales of fundamental molecular processes such as dissociation, rearrangement of molecular bonds, and vibrational motion. This can be exploited for creating “movies” of these processes in so-called pump-probe experiments. Here, the first (“pump”) laser pulse triggers the reaction of interest, and the second (“probe”) pulse, arriving after certain delay time, takes a snapshot of the molecular structure [1-3].

For the 2021 REU program, we offer a project focused on performing pump-probe experiments at the James R. Macdonald Laboratory using intense femtosecond laser pulses in the ultraviolet (UV) to near-infrared (NIR) spectral range. The main goal of these experiments will be to trace the time evolution of molecular reactions induced by either the UV or the NIR light pulse. Within the course of the project, the REU student will gain practical, hands-on experience working with ultrafast optics (in particular the characterization of femtosecond laser pulses), learn basics of laser interactions with atoms and molecules, get an introduction into electron and ion spectroscopy, and in the data acquisition and data analysis software for pump-probe experiments. The student will be co-mentored by Prof. Daniel Rolles and Prof. Artem Rudenko and work

1. S. Pathak et al., Nat. Chem. 12, 795-800 (2020).

2. Y. Malakar et al., Phys. Chem. Chem. Phys. 21, 14090-14102 (2019).

3. D. Rolles et al., Journal of Visualized Experiments 140, e57055 (2018).

Controlling and imaging how molecules vibrate, rotate, and dissociate with intense laser pulses (Theory)

Uwe Thumm

E-mail: thumm@phys.ksu.edu

Number of REU participants: 1

The dissociation of molecules by intense, short laser pulses is a fundamental physical light-matter-interaction process. The rotational and vibrational motion of small molecules and their fragmentation dynamics can be resolved in time by their repeated electronic excitation and/or ionization in ultrashort pump-laser pulses and the subsequent destructively imaging of the excited molecules with delayed ultrashort probe-laser pulse. In state-of-the-art atomic, molecular, and optical physics laboratories, this allows the detection of molecular-fragment momentum distributions (generated by the probe pulse) for a time series of pump-pulse – probe-pulse time delays. With the help of numerical simulations, such “molecular movies” then allow the distinction of molecular dissociation pathways, with implications on our understanding of molecular reactions in general.

Contributing towards this goal of understanding molecular dynamics in “real time”, i.e., with a time resolution of the order of 10-15 seconds, you will numerically solve the time-dependent Schrödinger equation for the vibrational and rotational dynamics of diatomic molecules interacting with intense, short laser pulses and calculate pump-probe-delay-dependent momentum distributions of molecular fragments. Analyzing your fragment-kinetic-energy-release spectra, will enable you to describe the bound and dissociative molecular motion, based on available electronic, vibrational, and rotation energy levels and their strong distortion by the intense laser electric field. In particular, your research may help unraveling the phenomenon of ``light-induced stabilization’’ i.e., the somewhat counterintuitive effect of molecular dissociation (for the right conditions) becoming less likely as the laser intensity is increased.