Assymetric temperature profile in DEVICE photothermal calculation


#1

Hi All,

I was calculating the temperature of plasmonic structures induced by photothermal heating and noticed that the results I output is somehow always assymetric (as below, why the temperature on the right side looks smaller than on the left side?). I wonder could you please give me some insights on what might be wrong?

I used FDTD to calculate the absorption profile of the plasmonic structure and then input the absorption profile into DEVICE to calculate the temperature profile, as instructed on Lumerical website: https://kb.lumerical.com/en/sp_photothermal-heating-in-plasmo.html

Thanks!
Zhaoxia


#2

BTW, the structure is periodic structure of gold nanoparticle arrays on glass substrate (not direct touch).


#3

Dear @zhaoxiaq

Can you please upload your simulation files (.fsp and .ldev) for a review?

Thanks


#4

Sure! Please see attached for the .fsp and .ldev files. I’m new to DEVICE but have been bothered by this problem for a long time. Thanks very much for your help!
4AuNP_PNIPAM3x3Array_H20_Pabs.fsp (309.1 KB)
4AuNP_PNIPAM3x3Array.ldev (7.7 MB) (heat solver is disabled to shrink the size of the file to below 8000K).


#5

Dear @zhaoxiaq

Regarding your optical simulations in FDTD, I recommend you to use periodic BC along the x and y direction to avoid edge effects. Doing so, absorbed power, obtained from analysis group, looks symmetric between different unit cells.

However your device is not symmetric and thus you should not expect symmetric results. Please note that 4-gold sphere in your simulations are positioned in a triangular shape, which point down and to the left in the plot that provided before. One thing to check the accuracy of your results is to have a symmetric design and repeat your simulations. The other thing to note is that in your Device simulations, your geometry is not a periodic structure thus, even with a symmetric geometry, devices at the center will get heated more than the ones on the boundaries.

Please let me know if you have any concerns and keep me updated of your results.

Thanks


#6

In the fsp file I shared with you, I tried using periodic BC along the x and y directions, but the simulated temperature profile is even more counter-intuitive (see below Image 1), even for symmetric structures (i.e., only one center particles instead of 4 in each individual domain). The other side effect is that the output pabs only contain data for the domain in the center (see Image 2 for pabs along z~0 plane (crossing the center of the NPs). That’s why I switch back to NOT using periodic BC condition. I’m quite confused. Do you have any other structures?

(Image 1)

(Image 2)


#7

Follow up on the previous question: using similar settings, if I change my structure into one single gold sphere with a diameter of 50 nm, I get the following Pabs profile at the z = 0 plane:

Then based on the pabs, I calculate the temperature profile in DEVICE. The 3D temperature monitor shows the following results:

The 2D temperature monitor at z = 0 plane shows the following results:

I wonder why the 2D and 3D temperature profile has such wield geometry. Or could anyone send me both FDTD and DEVICE files on how to calculate the temperature distribution of a spherical gold nanoparticle with a diameter of 50 nm and under 25mW 532 nm laser illumination? Thanks very much for your help!


#8

Dear @zhaoxiaq

If you have a periodic structure illuminated by plane source, you need to use periodic BCs. However, if you have an isolated device you will need to use PML BC with TFSF source surrounding your device. I thought that you have periodic device and that was the reason why I used periodic BCs. Please note that if you use plane source with PML BC, you will get artefacts called edge effects.

In your first plot, since the temperature is almost similar (300 K) all over device, the plot will not be precise. I recommend using a bigger scale factor (when you import absorption profile into heat solver) to better resolve the heat distribution profile. Part of problem can be also because of the coarse mesh which I explained below.

Regarding the weird sphere shape, I guess it is coming from course mesh. You can increase the mesh resolution in Device as is shown below:

Make sure that you have checked the box and you are using fine enough mesh. Then mesh the structure and visualize grid before running simulations to make sure that you have set it correctly.

The other thing is that simulating a periodic structure in Heat solver is not straight forward since your thermal simulations does not have periodic BCs. One workaround is to do convergence testing in which you start with one unit cell and run both optical and heat simulations to capture temperature profile. Then increase the number of unit cells and repeat the simulations until your temperature profile remains unchanged in the central unit cell. The heat profile in central unit will represent temperature distribution all over the geometry if you had periodic BCs.

I hope this will help you solve the problem.