If n is infinity, wavelength is equal to what?

[Amany Gouda]

in the dispersion relation of the surface plasmon

the wavelength is proportional to square root of n. according to equation 5 in this paper:
https://Newton.ex.ac.uk/research/emag/pubs/pdf/Barnes_JOA_2006.pdf
if n goes to infinity, then what will be the value of wavelength.
Thank you

 

[mfb]

I don't see any n that could go to infinity in equation 5, and if you let one of the ε go to infinity (keeping the other constant) the square root has a finite limit.