Instability when modelling gold in the wave optics transient model

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Dear COMSOL Forum

I am trying to simulate a gaussian pulse incident on a gold surface using the wave optics transient model. I created a model based on this tutorial: https://www.comsol.com/model/second-harmonic-generation-of-a-gaussian-beam-wave-optics-14701 and then added a material in the second half of the domain. As the wave optics transient model only uses the real part of the permittivity, I am inputting the imaginary part via a conductivity value instead. When I put in permittivity/conductivity values for a semiconductor the simulation runs well, showing a reflected and transmitted beam with the transmitted being slowly absorbed with distance. However, when I put in permittivity/conductivity values for gold the simulation initially runs, but then the electric field in the gold region becomes unstable - in some small region (and before the beam reaches the surface) the electric field strength rapidly goes to infinity and the simulation crashes. I have tried reducing the mesh size and timestep significantly, but this seems not to resolve the problem. Would someone be able to suggest a method to solve this?

Many thanks in advance.

Best wishes,

Alan


3 Replies Last Post 28 févr. 2025, 06:24 UTC−5
Ulf Olin COMSOL Employee

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Posted: 4 days ago 27 févr. 2025, 10:36 UTC−5
Updated: 4 days ago 27 févr. 2025, 10:37 UTC−5

Hi Alan, I split the domain in the SHG model you referred to and added Gold to the second half (with a conductivity of 45.6e6[S/m]). Compared to the original model, I made no other changes. In my simulation, everything worked. The Gaussian pulse was almost completely reflected, as expected. So, I could not reproduce the instability that you experienced. I suggest that you contact COMSOL support and let them take a look at your model. Best regards, Ulf Olin

Hi Alan, I split the domain in the SHG model you referred to and added Gold to the second half (with a conductivity of 45.6e6[S/m]). Compared to the original model, I made no other changes. In my simulation, everything worked. The Gaussian pulse was almost completely reflected, as expected. So, I could not reproduce the instability that you experienced. I suggest that you contact COMSOL support and let them take a look at your model. Best regards, Ulf Olin

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Posted: 4 days ago 27 févr. 2025, 13:09 UTC−5

Hi Ulf, many thanks for the message. Did you also update the real permittivity of gold? In case its useful I'm using a wavelength of 1030 nm, here its value is -44 roughly.

Best wishes, Alan

Hi Ulf, many thanks for the message. Did you also update the real permittivity of gold? In case its useful I'm using a wavelength of 1030 nm, here its value is -44 roughly. Best wishes, Alan

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Posted: 3 days ago 28 févr. 2025, 06:24 UTC−5

P.S. At 1030nm I believe the conductivity of gold is about 32000[S/m]?

P.S. At 1030nm I believe the conductivity of gold is about 32000[S/m]?

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