RUI: Understanding and Control of Strong-Field Molecular Ionization

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Ever since the development of the laser in the 1960's, scientists have sought to use lasers to directly influence chemical reactions. In this context, a pulse of laser light can be thought of as a new type of reagent that drives a chemical reaction. This project will advance the study of laser-assisted chemical reactions by making three-dimensional images of the products of such reactions. This science can contribute to the economy and to public well-being because development of these laser-based reagents could one day allow chemical synthesis of novel materials and medicines. Progress toward this goal is challenging, however, because molecules are so complicated and dynamic that it is difficult to determine the correct laser characteristics to drive a particular process. This project will use experimental feedback to guide an adaptive search of the possible laser pulses. This type of method is proven to work, but it is only as good as the feedback that drives it. The goal of these studies is to develop and exploit enhanced image-based feedback techniques that refine this approach to controlling chemical dynamics. Doing this work with undergraduate students also provides students with motivation for further scientific education and therefore helps develop a highly skilled workforce. Interactions between strong laser fields and polyatomic molecules are at the forefront of many aspects of ultrafast science. Shaped ultrafast laser pulses can powerfully influence molecular dynamics, thus allowing access to outcomes not typically available by other means. The area of emphasis of this research program is adaptive femtosecond control, in which a learning algorithm is used to guide the construction of shaped ultrafast laser pulses that produce a desired result. In order for the adaptive search to succeed, robust, well-defined feedback is required. To this end, this team developed the capacity to use three-dimensional momentum imaging of the laser-molecule reaction products. By applying rapid three-dimensional image-based feedback to the control of photoisomerization in small hydrocarbon molecules, this team is able to examine how manipulating the electronic excitation of the molecule influences the nuclear motion, and thus affects ultrafast chemical processes. Understanding basic strong-field processes helps to guide these coherent control protocols by allowing this team to link image-based feedback to specific target states. This team will pursue several experiments that can advance the understanding of how strong-field ionization occurs in polyatomic systems, including the role that field-dressed orbitals with strong Rydberg character have on tunneling ionization in polyatomic molecules.