Recent Advances in the EFISH Diagnostic for Electric Field Measurements*

1.  Electric Field-Induced Second Harmonic Generation (E-FISH)  a non-linear optical phenomenon initially investigated in the mid-1970s, has found renewed purpose as a method for electric field measurements in plasmas . Its straightforward implementation and excellent temporal resolution make it particularly suitable for analyzing pulsed, non-equilibrium discharges . Beyond its ability to resolve orthogonal components of the electric field vector , E-FISH can also provide 1-D and 2-D electric field information . The method’s continued popularity is evident from recent reviews on this topic .
   
   However, research has highlighted certain limitations of the E-FISH method, especially when using focused laser beams. The coherent signal generation, in the direction of beam propagation, renders it sensitive to the Gouy phase shift of the probe beam along this path. Consequently, the signal depends on the entire shape of the electric field profile, rather than solely the local value within the beam focus (where the intensity peaks) . This introduces additional uncertainty, as the electric field strength—the quantity to be measured—often lacks a precisely known profile shape.
   
   This talk will discuss some of the recent attempts at addressing this issue, particularly the use of machine learning methods which have demonstrated considerable promise. In addition, the combination of the EFISH method with other diagnostic approaches will also be presented.