I am from University of Minnesota and is currently using FDTD to solve for a light absorption problem. The geometry looks like this:
Geometry: the gray area has x span = 22 um, y span = 15 um and it is 2D. The FDTD solver x span is 22 um with PML boundary condition on all size.
I had set the Gaussian beam with r = 6 um, amplitude = 1, pulse duration of 1 picosecond, and wavelength of 783 nm (a single wavelength only.) The diameter is less than the x span so I think I do not have to worry about boundary conditions.
My FDTD simulation time is 6000 fs.
Then I used solar generation analysis group to calculate the power absorption inside my materials. I used mesh accuracy of 7 and auto shutoff of 1E-6. The result looks like this:
I am wondering if I did everything correctly. This contour map does not look smooth as I would expect to see a smooth Gaussian shape contour map.
I am also curious how to give the Gaussian beam an absolute power amplitude. Right now I can only set an unitless amplitude of 1, but I would like to set an absolute amplitude (something like 20 mW.)
I also don’t know how to interpret the solar generation absorption result (Pabs). The Pabs has the unit of [fraction of source power/m^3] according to the comments in the script and this number is greater than 1, which is counter-intuitive since I would expect a fraction to be less than 1. Can I convert this number to an absolute power in unit of W?
Thank you for any help. Let me know if you need more specific information about how I set up the simulation.