“Appropriate Modeling Approach for Thin Plasma Layers”

[rcc01]

TL;DR

Asking whether a micron‑scale, low‑density plasma layer can be modeled with standard cold‑plasma permittivity or requires a full inhomogeneous Maxwell treatment, and whether thin‑film approximations (surface impedance, effective index) are valid.

I’m trying to understand how to model EM wave propagation through a very thin, low‑density plasma layer (micron‑scale thickness). The plasma frequency is well below optical frequencies, so the layer remains transparent.

My questions are:

1. Can such a thin plasma sheet be treated using the standard cold‑plasma permittivity model ε(ω)=1−ωp2/ω2 or do the boundary conditions imposed by the adjacent dielectrics require a full inhomogeneous Maxwell solution?
2. Are there known approximations for phase delay or index modulation caused by a thin plasma sheet, similar to ionospheric phase‑shift models?
3. Does the thin‑film geometry allow simplifications such as treating the plasma as a surface impedance or effective boundary layer?

I’m not asking about any device specifics — just the appropriate modeling approach for thin, low‑density plasma layers.

P.S. I previously posted a more optics‑focused version of this question in the Optics section. I’m posting this version here because I’d appreciate input from plasma specialists on the thin‑film case.