Development of nonlinear optics-based reduced electric field diagnostics

Abstract

This thesis presents the development and application of advanced nonlinear optical diagnostics for electric field and number density measurements in gaseous plasmas. Leveraging Electric Field Induced Second Harmonic Generation (E-FISH), a highly sensitive diagnostic setup was designed to achieve sub-1 V/cm electric field detection in atmospheric pressure air with picosecond temporal resolution. This represents a 2 to 3-order-of-magnitude improvement over conventional E-FISH approaches. A passive homodyne detection mechanism, arising from the interference between E-FISH signals and stray surface-generated second harmonic signals, was analytically modeled and experimentally validated. This mechanism also enabled polarity sensitivity, a key advancement for diagnosing electric field reversals in plasma discharges. Additionally, the thesis reports the experimental observation of non-resonant, second-order sum-frequency generation (SFG) in five different gases. The observed SFG signals demonstrate quadratic scaling with gas pressure and insensitivity to applied electric fields. Together, these diagnostics offer new capabilities for spatially and temporally resolved mapping of electric fields and gas densities in reactive flows and plasma environments, advancing our ability to probe and model transient plasma phenomena.