Learning Forum

[APat]

Dear Concerned Personnel,

I wanted to ask a fundamental question pertaining to the procedures following calculation of reflectance/transmittance using DFT power monitors. During the calculations of reflectance/transmittance from a scattering sample, when we are using a broadband plane-wave source as the incident beam, how does the beam profile shape (broadband source) affect the calculation? Do we normalize the measured reflectance/transmittance by the incident beam profile?

Please let me know if my question is not clear or requires more elaboration.

Thanking you,

Best regards,

Anvay.

[Taylor Robertson]

Simple plane wave sources shouldn't have a beam profile, and even if they did, that would not matter to the power transmission calculation. The power transmission is calculated in the DFT monitor by the flux of the Poynting vector through the monitor plane, so you can use Beam or Diffracting plane wave sources without an issue. This is normalized to the injected power, under most normalization options.
One thing to be careful of is that the injection angle for plane waves at non normal incidence can vary with frequency. Using a BFAST plane wave hat it is designed to counteract this effect. For a broadband simple plane wave you would need to be aware of this fact, but you may be able to interpolate the data if you are sweeping over many incidence angles.
https://support.lumerical.com/hc/en-us/articles/360034382894-Understanding-injection-angles-in-broadband-simulations

[APat]

Dear Thank you very much for your answer! Following your comments, is it right to assume that even if we import a custom lamp beam profile, the output that we shall get from power transmission calculation would be the same as that obtained from a plane wave profile? When I say same output, I am referring to the shape of the reflectance/transmittance profile after light interaction with a particular scattering sample. Please let me know if I have got it all wrong.
Best regards Anvay.

[APat]

Dearand Support Team,
This is a gentle reminder to please address the question posted in the earlier thread? I shall be very grateful to you.
Thanking you in advance Best regards Anvay.

[Taylor Robertson]

Sorry for the delayed response, we are very busy around here lately :)
I am not sure what you mean by "lamp beam profile". This would be a custom source using a field profile you imported?
So the resultant power is by default normalized to import source field profile spectrum. As long as you know the input power (radiometric W/m^2/nm), you can multiply this value by the normalized transmission from FDTD to get the output power of an experimental set-up. You would need to know the input power, but you shouldn't need to perform any further normalization. You can change how the normalization is calculated, which may be important if you have multiple sources, or scale the field amplitude in nonlinear simulations.

Here are some more resources you may find useful.
https://support.lumerical.com/hc/en-us/articles/360034394234-Understanding-frequency-domain-CW-normalization
https://support.lumerical.com/hc/en-us/articles/360034925373-sourceintensity-Script-command
https://support.lumerical.com/hc/en-us/articles/360034915813-Impulse-Analysis-Calculating-the-response-to-an-arbitrary-time-signal-using-the-impulse-response
https://support.lumerical.com/hc/en-us/articles/360034383014-Import-source-Simulation-object
Best Regards

[APat]

Dear No worries about the delay! I can understand. :)
You are correct about the interpretation when I say "lamp beam profile". I believe the additional explanation and resources you provided are very useful. If I have any more questions, I shall reach out to you and the team.
Thanking you once again for taking out time Best regards Anvay.