RUI: Using Imaging Methods to Expose the Molecular Dynamics Arising from Ultrafast Adaptive Control

Augustana University Association, Sioux Falls SD

Investigators

Abstract

Shaped ultrafast laser pulses can powerfully influence molecular dynamics, thus allowing access to outcomes not typically available by other means. The complexities of the field-molecule interaction generally make an a priori determination of the required field characteristics impossible, and so adaptive feedback algorithms are often employed to identify the optimal pulse. This technique efficiently selects pulses that enhance the desired pathway. Exactly how this is accomplished, however, is often obscure. This research examines ways to extract mechanistic information from closed-loop control by approaching this problem from the perspective of the feedback signal. By incorporating images into the feedback loop or using vibrational-state specific feedback we can query the search algorithm in very specific ways. Correlation of small changes in the feedback target with changes in the optimal pulse traits can lead to mechanistic insight. Furthermore, the mechanisms underlying the control can be subsequently probed with the power of velocity map imaging (VMI) or cold-target recoil-ion momentum spectroscopy (COLTRIMS). Experiments will be conducted at Kansas State University with much of the pre- and post-experiment work carried out at Augustana College. The primary aim of these experiments is to uncover the fundamentals of the molecular dynamics in these interactions. To this end, we will construct, test, and incorporate into the feedback loop a Doppler-free kinetic energy release spectrometer that is capable of resolving specific vibrational states of CO2+ through its dissociation into C+ + O+. Using this high resolution feedback, we will seek to manipulate the vibrational population and thereby gain a window into the dynamics leading to population of the transient CO2+. Using VMI as feedback allows simultaneous access to angular and kinetic energy release (KER) information for a given ion species. Shaped pulses will be used to control the isomerization of the acetylene di-cation into CH2 + + C+ and the ethylene cation into CH3 + + CH. Both of these processes can be probed with VMI and/or COLTRIMS. Understanding how isomerization is controlled in these benchmark hydrocarbons can provide a foundation for improved control in larger molecules. A concurrent secondary direction will be the implementation of new feedback techniques for adaptive control, such as the rapid inversion of VMI spectra to obtain unambiguous KER data. Broader Impacts: This work integrates undergraduates at all levels, from experiment design to manuscript preparation. Experience has shown that this activity both encourages students to continue their science training and provides a strong background for graduate work. The group has a good record of promoting the participation of women in physics. Scientifically, improved understanding of the molecular dynamics involved in closed-loop coherent control will benefit several applications, including detection of trace amounts of materials with undesirable environmental or national security traits and the use of shaped pulses for the creation of molecular qubits for quantum computing. Improved understanding of how isomerization dynamics can be manipulated could further enable the development of molecular switches and laser-controlled chemical synthesis. Dissemination of results will occur through peer-reviewed publications, conference presentations, and seminars and symposiums that often feature students.