New Laser-Induced Fluorescence-Dip Spectroscopy for Weak Electric Field Measurements in Plasma

Abstract

In laser-induced fluorescence-dip spectroscopy the resonance range of the Stark-shift is probed by tuning the excitation laser when measuring the absorption spectra [1] . Thus, in order to work out a single measuring point a very reproducible field distribution in the plasma over time or from pulse to pulse is required. The new method enables the measurement range to be extended to plasmas in pulsed systems with frequently poor microscale pulse-to-pulse reproducibility. The core element of the diagnostics is a special broadband dye laser for the excitation of Rydberg levels in xenon. With a bandwidth of 1 nm, it is possible to record a wide range of Stark shifts in just one measurement step. Depending on the applications, two variants of diagnostics can be used either independently or in addition: semi-quantitative determination of the one-dimensional electric field distribution stretched to the area of a few cm and spot measurement of the field strength with high spatial and spectral resolution. The proposed diagnostic enables the measurement of electric fields with high temporal (5 ns) and spatial (tens of μm) resolution with sensitivity of 200 V/cm and accuracy of 20 V/cm. However, this is not the limit of the diagnosis. The sensitivity can be lower than 100 V / cm if higher principal quantum numbers are chosen for the Rydberg levels (n> 20).