Goos-Hänchen effect.

source
optics

#1

Hi,
I was just curious to see the effect of Goos-Hänchen effect. So I decided to visualized this effect based on the information available on this webpage.

http://pages.uoregon.edu/noeckel/gooshanchen/

I made the simulation structure based on the information available on webpage. But unfortunately, unable to see the effect properly. Can somebody tell what should be be correct source to visualized this effect more appropriately. And why I am getting reflection from the boundary, even in simulation I have made PML boundary to avoid reflection.

Thanks in advance. GS_test.fsp (301.4 KB)


How to display light propagation in a single image using FDTD solution
#2

Hi @visvas

Before we jump into the simulations, do you know how much shift we would expect?

I guess the best approach would be to use Gaussian source. Extra care is needed to remove the numerical noises but we can work on it.

Your structure needs to extend the PML layer to avoid the reflection. At the moment software assumes that there is a gap between GaAs and PML.

A few notes: I guess you can do a 2D simulations rather than 3D. This should enhance your simulation time significantly. You can choose a material with constant refractive index to ignore the dispersion on your simulations. Please note that the injected source is defined in time domain and you can’t have a single frequency injection. Also, you don’t need to define a second object with refractive index of 1 as software assumes that background index is 1. This means that any area that does not have any objects is air.

Please let me know how your simulation goes and we can discuss it further.


#3

Unfortunately, I have no data set. But, I expect that it should be significant as shown in movie (see link). I will be thankful if someone gives more accurate data set.
Few more points related to simulation ;

  1. First of all, the simulation PML boundary are exactly close to structure. But any way, I will extend it further. Maybe, reflection is coming from this problem.
  2. Its simple simulation, so even 2 D or 3 D is not a problem, its only few seconds need to simulate, so I don’t care.
  3. Since wavelength is already fixed at 8 micron (initial and final values), so I am unable to understand how dispersion can come into picture. It will be by default a fixed value for one wavelength.
  4. Source is defined in time domain, but only for one wavelength, So I didn’t get how other wavelength can come into picture. Should I defined the source in frequency domain ?
  5. Finally, I am excited to study the effect of spin wave with plasmonics wave, so I intentionally added two layer material, infact I agree that here it has no sense, since background refractive index is same.

Please let me know what should I do with source setting.


#4

Dear @visvas

Its good to have some numbers to compare simulations with theoretical values. Maybe this paper has more detailed information and we can try to replicate their results.

The FDTD runs in time domain. This means that if you want to have a single frequency source, you need an infinitely long time domain signal. Even if you set your signal at signal frequency, software automatically chooses a pulse which includes other frequencies. Thus this might cause dispersion that are non-desirable but choosing a material with constant index will avoid the problem.

It will be a good idea if you start with some of our getting started examples and watching webinars.

You can use a Gaussian beam with lower NA (say 0.2). Adjusting beam diameter and lens diameter from beam options-> use thin lens (say to 500 um) might be a good idea so that the injected Gaussian profile in your simulations closely matches with the one from theory. Also, do you have any idea how you want to measure the shift?

This is an interesting problem to study. Maybe we can try to replicate the results of some published papers.


#5

Thank for your intresting reply. I have updated this file. Now the refrective index of the medium 2 is 3.3 fixed value. And I have applied a thin lens of 50 um only. It looks like lot of enery is dissipiated in boundary interface, which results in no reflection (or poor reflection). But according to webpage refrence, 32 degree is the angle of total reflection. So the simulation need to modify further more.
Lastly you have pointed out nice refrence, after reading this article, it looks like GS shift is polorisation dependent (see figure and equation 1 of your refrence), but I think it is not possible to set perticular polorisation in gaussian source.

Anyway, I need to study more, let me know if you get any more improvement in result. GS_test.fsp (235.8 KB)

get back to you soon with better understanding.


#6

You can set the polarization angle (degrees) to 90 from the Edit Gaussian source tab. This will change the polarization of light.

To Gaussian beam profile requires some modification to generate a perfect Gaussian source. You can increase the angle to 60 degrees to make sure that all the light is reflected within numerical errors. Feel free to adjust beam settings and add monitors (such as a movie monitor to watch the light propagation and Frequency domain field and power monitor to plots transmission and reflection).

I am hoping to simulate this effect as it is an interesting phenomena that I was not aware of that before. So, thanks for bringing this into my attention :slight_smile: