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Poynting Vector Direction for Au Nanosphere in Water (Wave Optics Simulation)

Posted 28.11.2024, 13:55 MEZ Wave Optics, Results & Visualization, Physics Interfaces Version 5.4 2 Replies

Jiseok Han
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I am conducting a wave optics simulation using COMSOL to study the optical properties of a gold (Au) nanosphere immersed in water under visible light illumination.

During the simulation, I visualized the Poynting vector on the particle's surface.

Surprisingly, I observed that the Poynting vectors are not only directed outward but also inward towards the particle (as shown in the attached image).

I have the following questions regarding this observation:

  1. Why are some of the Poynting vectors directed inward toward the particle?
  2. What is the physical significance of these inward-directed Poynting vectors?
  3. Is this phenomenon independent of absorption, or is it related to the absorption of the nanosphere?

To aid understanding and provide additional context, I have attached both the figure illustrating the Poynting vector distribution.

Thank you for your time and expertise.

Kind regards, Jiseok Han

2 Replies Last Post 29.11.2024, 05:38 MEZ
David Greve
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Posted: 6 months ago 28.11.2024, 22:35 MEZ

I think some of the older Comsol versions compute the average of the inside and outside values when asked to evaluate a quantity on the boundary. You might want to try evaluating on a surface a little inside and outside the boundary.

I think some of the older Comsol versions compute the average of the inside and outside values when asked to evaluate a quantity on the boundary. You might want to try evaluating on a surface a little inside and outside the boundary.
Jiseok Han
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Posted: 6 months ago 29.11.2024, 05:38 MEZ
Updated: 6 months ago 29.11.2024, 05:39 MEZ

Dear David Greve,

Thank you for your helpful suggestion. If I understood correctly, you are advising me to plot the arrows slightly inside and outside the surface of the gold particle.

Following your advice, I evaluated the Poynting vector at intervals of 1 nm both inside and outside the particle's surface. However, I still observe Poynting vectors directed inward toward the particle, even when evaluating slightly away from the boundary.

I am curious to know if this result makes physical sense or if it could indicate an issue with the simulation setup or interpretation. I would greatly appreciate your insights regarding whether such inward-directed Poynting vectors are consistent with physical phenomena.

Thank you again for your time and valuable feedback.

Best regards, Jiseok Han

Dear David Greve, Thank you for your helpful suggestion. If I understood correctly, you are advising me to plot the arrows slightly inside and outside the surface of the gold particle. Following your advice, I evaluated the Poynting vector at intervals of 1 nm both inside and outside the particle's surface. However, I still observe Poynting vectors directed inward toward the particle, even when evaluating slightly away from the boundary. I am curious to know if this result makes physical sense or if it could indicate an issue with the simulation setup or interpretation. I would greatly appreciate your insights regarding whether such inward-directed Poynting vectors are consistent with physical phenomena. Thank you again for your time and valuable feedback. Best regards, Jiseok Han

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