Learning Forum

[nerrror]

Hello,

I am trying to understand exactly what the farfield functions from lumerical compute from the monitor in the near field.

Is it computing the Fourier Transformation of the harmonic components of the recorded fields or are they computed differently? I am unsure since the Fraunhofer approximation should only apply if either the source or the field in the distance is a plane wave which is not true in my case.

Finally, I would like to invert the farfield function such that I can compute the near field from a given electric field in the farfield or (if that's possible) from the farfield intensity. How would I do that?

I would kindly appreciate any information or literature hints on my question!

Regards

[Guilin Sun]

You are right that the Fraunhofer approximation should only apply the largest diffraction angle is very small, which could be found in Goodman's Fourier Optics.
No, it is not simply the Fourier Transformation. It uses the equivalent principle which may be found in advanced electromagnetics.

From the farfield to near field, it is doable, provided that you have far field angular distributions (not intensity). Example can be found here https://support.lumerical.com/hc/en-us/articles/360041781874-Photolithographic-projection-to-photoresist
Basically, it propagates the decomposed plane waves to the given near-field plane.

However, if you only have far field intensity, the phase information is lost. You may not get accurate near-fields from intensity quantity, since the initial phase place important role in interference.