Measurement of two-dimensional distribution of electric fields in collisional environments.*

In this presentation we describe a picosecond pump-probe method termed laser induced fluorescence dip (LIF-dip) spectroscopy for interrogating electric fields in medium pressure (200 Torr) plasma discharges. We employ an intense picosecond pump laser to drive two-photon absorption on a Kr seed immersed in a helium environment. Specifically, we utilize \textasciitilde 202.3 nm to excite the Kr from the ground state to the 5p$^{\mathrm{\mbox{'}}}$[\textonehalf ]$_{\mathrm{0}}$ state. Shortly after excitation, a second tunable picosecond laser excites the 5p$^{\mathrm{\mbox{'}}}$[\textonehalf ]$_{\mathrm{0}}$ state to (Stark shifted) n $=$ 11 to n $=$ 25 Rydberg states causing a depletion in the observed fluorescence of the excited state to the 5s'[3/2]$_{\mathrm{1}}$. The electric field dependence of the Stark shifted Rydberg states is experimentally measured for a few select Rydberg states to provide electric field detection spanning \textasciitilde 500 V/cm to 10 kV/cm and then utilized to asses electric field distributions. We also discuss the use of a least-squares fitting procedure with additive gaussian noise-based approach to assign observed LIF-Dip profiles electric field values.