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# How can I model a GAUSSIAN source in 3d-FDTD?

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#### Rastegarfar

##### Newbie level 4
gaussian source

I have to simulate the propagation of intense laser light in a nonlinear medium(STUDYING THE OPTICAL KERR EFFECT)
This has to be done using the fdtd method. Can anybody help me?

gaussian plane wave source in fdtd

Why do you have to use FDTD? Have you considered a beam propagation method (BPM)? These are very popular for nonlinear optics simulations and they are easier to implement.

I am not sure of your exact application, but you will likely want to implement your source using the total-field/scattered-field (TF/SF) approach. I describe doing this for plane wave sources in my dissertation. You can download it here:

It is also described in Taflove's book on FDTD which has been uploaded somewhere to the EDABoard E-books forum.

You will need to modify the TF/SF technique to inject a Gaussian source, but the implementation is exactly the same as a plane wave source. Instead of a uniform amplitude and phase, your source will be Gaussian.

I will warn you that the math describing a Gaussian light beam is derived using the paraxial approximation so it does not rigorously satisfy Maxwell's equations. If you try to inject this directly in FDTD (a rigorous technique), you may get some crazy results. I have three suggestions for you:

1. Do a literature search to see if this has been done before and how they did it.
2. Pass a plane wave source through an aperture to construct your Gaussian beam. It can be a lossy dielectric aperture to vary the amplitude and phase as well.
3. You can just use (2) as your source, or you can record the amplitude and phase of this source and just incorporate that directly into your model using TF/SF. You can be sure this source will rigorously satisfy Maxwell's equations so you won't get any strange behavior.

Good luck!!
-Tip

3d fdtd equations

Hi Dear Rastgarfa!

1- I suggest you refer to Sullivan's book about FDTD(IEEE publishing), rather than Taflov's. because the formet is smaller and easier to handle in less time. for furthure reading you can refer to Taflov's Book which is like a good dictionary in FDTD topic.

2- I think you can use some softwares in this area such as: XFDTD from Remcom, FDTD solutions from Lumerical ,.... but I'm not sure about Non-linear effects!

Hamid.

### Rastegarfar

Points: 2
fdtd lossy dielectric

use optiFDTD v6 or higher version

optifdtd thesis

Dear Tip,

I would like to thank so much for your kind reply, ans also dedicating your valuable time to me. Your guides will certainly help me to a great extent.

Best wishes,
Houman

Added after 22 minutes:

Dear a_shamsafar,hamid2000,rrumpf:

Thank you very much for your kind answers. I sincerely hope for your success.

tfsf 3d gaussian planewave

Dear Houman, HI

I also appreciate you.

Regards
Hamid

gaussian beam propagation + with fdtd

hello,rrumpf, why I can't connect the link you provide?

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