How one should excite Surface Plasmon Polaritons on a prism?

In summary, the conversation discusses a problem with a laser experiment using the Kretschmann configuration. The speaker has a red laser, goniometer, photoreceptor, and right angle prism coated with gold. They are not seeing the expected intensity dip and are considering possible causes such as imperfections in the prism, misalignment of the laser, ambient light, and rotation offsets. The expert suggests checking the laser alignment first and then addressing any possible rotation offsets or imperfections in the prism.
  • #1
TheFerruccio
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I've got a red laser, goniometer for aligning the angles, photoreceptor that outputs values...

I've got a right angle prism with a ~40nm gold coating on the diagonal, and I *should* be getting some sort of dip in the intensity at certain angles, as P-polarized EM waves should be absorbed into SPP resonance, but I am not getting this intensity dip at all. I'm using the Kretschmann configuration for this experiment. The laser is in the red part of the spectrum.

I have a few possible leads, but which ones do you think would be a waste of time to correct, or which one do you think I should look at first?

1: Prism isn't perfectly smooth and polished
2: The alignment of the laser isn't 100% exactly in the center of the photoreceptor aperture, which is an order of magnitude larger in radius than the laser dot
3: There was mild ambient light in the room where the measurements were taking place (lights were off, though)
4: Some possible slight 1-2 degree offset in rotation on an axis normal to the prism's diagonal
5: The dip that causes SPP resonance is immeasurably small, given the power of the laser, and the sensitivity of the photoreceptor
 
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  • #2
I would suggest starting with the alignment of the laser, as that is the most likely culprit of why you are not seeing the intensity dip. Make sure that it is centered in the photoreceptor aperture and that it is aligned correctly. If that does not resolve the issue, then you can move on to check for any possible offsets in the rotation of the prism. Finally, you should check the smoothness and polish of the right angle prism to make sure that it is not causing any issues.
 

1. How do you calculate the optimal angle for exciting Surface Plasmon Polaritons on a prism?

The optimal angle for exciting Surface Plasmon Polaritons on a prism can be calculated using the equation θ = arcsin(η/np), where η is the refractive index of the prism and np is the refractive index of the plasmonic material.

2. Can Surface Plasmon Polaritons be excited on any type of prism?

Yes, Surface Plasmon Polaritons can be excited on any type of prism as long as the prism has a higher refractive index than the surrounding medium and is in contact with a plasmonic material.

3. What is the role of the incident light's wavelength in exciting Surface Plasmon Polaritons on a prism?

The wavelength of the incident light plays a critical role in exciting Surface Plasmon Polaritons on a prism. It must match the resonance condition of the plasmonic material in order to efficiently excite the polaritons.

4. Can Surface Plasmon Polaritons be excited with non-polarized light on a prism?

Yes, Surface Plasmon Polaritons can be excited with non-polarized light on a prism. However, polarized light is more efficient in exciting the polaritons as it has a specific direction of oscillation that matches the resonance condition of the plasmonic material.

5. How does the thickness of the metal layer on a prism affect the excitation of Surface Plasmon Polaritons?

The thickness of the metal layer on a prism can significantly affect the excitation of Surface Plasmon Polaritons. A thicker metal layer can lead to higher absorption and lower propagation length of the polaritons, while a thinner layer can result in a lower excitation efficiency.

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