How one should excite Surface Plasmon Polaritons on a prism?

TheFerruccio

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