Shift of absorbance peak when we modify the wavelength span.

    • Mickael Aelbrecht

      Hello everyone!

      My name is Mickaël Aelbrecht and I am currently in internship, working on Lumerical FDTD. The goal of my internship is to simulate the absorbance and scattering of a system. Unfortunately, I discovered that when I modify the span from 400-800nm to 500-600nm for example, the absorbance is shifted like so:

      My first hypothesis was that the source was centered anymore. But it is not the problem since the curve in red is 500-700nm and there is still this phenomenon occuring.

      Is there any way to prevent my simulations to do so ? How can I be sure that my simulation is accurate ?

      Thanks for considering my demand.

      Mickaël Aelbrecht

    • Guilin Sun
      Ansys Employee

      This is common when you change the source spectrum but do not modify other settings. It is usually due to two causes:

      1: when the min wavelength changes, the mesh will be changed in general. This is because the min mesh size is determined by the min wavelength, or more specifically, the min wavelengh in highest refractive index material.

      2: when the source spectrum changes, the material fitting will usually change, except the materials are non-dispersive.

      To avoid this, you can either tick "set simulation bandwidth":


      or set mesh generation bandwidth and material fitting bandwidth:

    • Mickael Aelbrecht

      Thanks a lot for your answer! Apparently this will work! I will try it out and come back to tell you about my experiments. Thanks again!

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