# Input power FDTD and its effect on T increase Heat

#1

Hello,
I’m using heat device to solve the temperature rise in a single antenna. My power irradiance is 4x10^(8) W/m2. My particle is a gold-disc of radius 50 nm and height 20 nm over a glass substrate. The size of my pabs_adv monitor is 0.5x1.5x0.08 µm3. In order to adapt the power of the FDTD simulation to my experiment there is the normalizing coefficient “input_power” in the pabs-adv. I was expecting having the same temperature rise/same power absorbed regardless of the size of my pabs-adv monitor if I adjust the “input_power” accordingly (input_power=irradiance x monitor area). But this was not the case. How should I calculate my “input_power”?

Regarding the unit of power absorption per unit volume (Pabs)
#2

I am a bit confused! Is gold disk the only object in your simulation region? If pabs-adv covers your object, I expect you get the same value for absorbed power even if you change the geometry of pabs-adv analysis group. Can you please upload your simulation file for review?

Sourcepower is the command to calculate inject power into your simulation are. This value depends on the size of the source and the bandwidth of injected light.

Thanks

#3

Thank you for your reply. Though we don’t seem to be on the same page. In the example you give on thermoplasmonic antenna (diabolo versus diapole antenna) you show that in the Pabs_adv monitor there is a parameter called input_power where the Pabs final is calculated: Pabs = Pabs * input_power;
it is made to normalize the sourcepower (which is equal to 1W in general) to the real power your antenna is receiving (so that you proceed to calculate the temperature in your special case). In my special case the experimental input_power is 4x10e8 W/m2 (it is irradiance, total power is 270 mW) how shall I calculate my input_power (I do have only one antenna) shall mulitply my irradiance by the area of my Pabs_adv monitor? here attached my file.
Thank you in advancetest.fsp (272.6 KB)

#4

Dear @abeer.al-mohtar

Sorry for the confusion. I will try to explain how the modified pabs_adv analysis group works in the Photothermal Heating in Plasmonic Nanostructures case.

First, absorbed heat is calculated inside the pabs_adv analysis box using the equations in the theory section of this page. By dividing this value to sourcepower(f) (line 132 of the pabs_adv script) we calculate the portion of the light that is absorbed (say 5% at 530nm). As you mentioned, this is proportional to having a 1W input power.

However, if your input power is less, for example 0.27 W, you need to multiply absorbed power with input-power: Pabs = Pabs * input_power (line 136).

Looking into your simulation file, it looks like you are using a TFSF source and pabs_adv that encompasses your gold disk. If substrate has a negligible absorption, you can set its index to 1.46 (so that imaginary part is zero). Doing this, you shouldn’t expect any change in absorbed heat as you change the pabs_adv analysis group region (gold disk would be the only absorbing material).

To calculate the input power, I guess irradiance will be more reliable. Since the size of your source is (x span, y span, z span)= (1, 1, 1) um^3 and it travels along z-direction, your input-power would be irradiance * x span * y span= 0.4 mW. Please note that this value is lower than 270 mW, as most of the emitted light in your experiment is not shined on the gold disk.