ECLIPSE: Exploring physics of Multiphoton Ionization using Thomson Coherent Microwave Scattering

Purdue University, West Lafayette IN

Investigators

Abstract

This award supports an effort to develop a database of plasma photoionization processes that are of great practical importance for applications such as combustion and high-speed aerodynamics. Ionization of gas by means of intense laser radiation, a process known as photoionization, is important in the research fields of gaseous discharges and optics; and photoionization is broadly utilized in state-of-the-art optical diagnostics of combustion and high-speed aerodynamic flows, as well as in generation of laser filaments. However, numerous photoionization processes utilized daily in these research fields are weakly characterized, which can cause ambiguities. This project will utilize a novel technique to study a number of specific photoionization processes of particular relevance to the practical applications. The broader impacts of the project will also include engagement and mentorship of undergraduate and graduate students who will be involved in the project, and integration of the research results into several graduate-level courses. Wide general audiences will be reached via the production of a series of educational YouTube videos on plasma science topics. The project will use the recently developed method of Thomson in-phase coherent microwave scattering (TMS) to precisely characterize and understand photoionization processes that have great practical importance in multiple research fields. These fields include nonlinear optics and filamentation physics, as well as optical diagnostics of gaseous discharges, combustion, and high-speed aerodynamic flows. The diagnostics methods that rely on the knowledge of the photoionization processes include electric-field induced second harmonic generation, two-photon laser induced fluorescence, and femtosecond laser electronic excitation tagging velocimetry. Specific research goals of the project include the development of a vacuum testing facility equipped with the TMS system and with an anechoic environment ideal for isolating the scattered signal from background environmental reflections, and characterization of the photoionization rates for several processes in a broad range of intensities up to ~ 100 TW/cm^2. This includes non-resonant photoionization of air, N2, O2, H2O, Ar, CO2, Ne, He, Kr, Xe, H2, and CH4 at 800 nm, non-resonant photoionization of He and N2 at 1064 nm, and (2 + 1) resonance-enhanced multiphoton ionization of CO at 230.1 nm, NH3 at 305 nm, and H2O at 248.3 nm. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.