How to generate a plane wave from "surface current"

Hi all,

I'm currently doing a simulation about the photothermal effect of nanoparticles. I'm planning to repeat a simple example in the reference (pubs.rsc.org/en/content/articlepdf/2012/lc/c2lc40495h) which is heating a gold NP in the water. The problem I met is how to generate a plane wave from surface current. I tried to set a number and I did get the plane wave, but how to change the wavelength?

I really appreciate any help.

Thanks a lot.

Bob,