Purcell factor calculation

Sangyeon_ChoSangyeon_Cho Member Posts: 4

Hi Lumerical,

I am Sangyeon Cho, a post-doc researcher at Harvard Medical School.

I am writing this thread to ask you about the Purcell factor.

I found that the dipole source generates the result of the Purcell factor after the simulation under the option of recording the local field.

I am trying to use this option to calculate spatial Purcell factor distribution by putting the dipole in the random position.

However, I cannot find the details of how FDTD calculates the Purcell factor using this option on the website.

Would you explain the details of it?

For example, FDTD generates a box with a certain size to measure emitting power? What would be the size of the box?

I appreciate your reply in advance.


  • gsungsun Posts: 1,376Ansys Employee

    Inside the dipole source, you can directly extract the Purcell factor, which is simply the ratio of actual radiated power and the power in the uniform material. Please refer this article


    and here https://support.lumerical.com/hc/en-us/articles/360034382794-Dipole-source-Simulation-object

    In lossy material, the dipolepower function may not work well: dipolepower - Script command

    This is why the box monitor group is used. In highly lossy material, it can be very challenge to get accurate radiated power. There is no strict requirement for the box size: if it is too small, the power integration may not be accurate; if it is too large, some power may be absorbed inside the box. So there is always a trade-off.

    Another thing to take care is: dipole radiated power may be very sensitive to its location in the Yee cell. This is because the 6 components of E and H internally are interleaved:

    ideally, the polarized dipole should be located on the correspondent location, eg, Ex polarized dipole should be located at Ex point in Yee cell. In your case, if it is randomly located, the Purcell factor map may not be very smooth.

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