Hello,
I just started reading about plasmonics and I have few doubts. I googled a lot but couldn't find concrete answer.
Please correct me if I'm wrong:
- Plasmon is quantum of plasma oscillation: Charge density oscillation (free electrons) on any surface [electrons vibrate around their equilibrium positions at certain characteristic frequencies called plasma frequency, which depends only on the number density of electrons, electric charge, electron mass and permittivity of free space].
- Surface plasmon resonance is the phenomena or event of coupling of EM wave with oscillating conduction electrons of the metal nanofilm.
- Surface plasmon polariton is the propagating EM wave generated at the metal-dielctric interface that propagates along the surface of the metal film after surface plasmon resonance.
- But Peter Y. Yu's answer confused me. He said that " To form a SPP, the photon and SPR must have the same frequency and wave vector" in Link: (https://www.researchgate.net/post/Is_there_any_differences_between_Surface_plasmon_polariton_and_surface_plasmon_resonance)
- How SPR can couple with photon since it is a phenomena?
- I've seen people mentioning about dipoles, SPR and SPP. What is the relation?
- In wire grid polarizer TM passes because dipole form , they couple and radiate. How is plasmonic effect really involved in the working of Wire grid polarizer?
Thank you.
Dear Ambar Shukla , I agree, when one is starting in this field the terms couls be puzzling.
-Not any surface can produce plasmons, you need free electrons to cause the oscillation, so a metal or an electron rich material would be necessary.
-To many and for the sake of simplification SPR and SPP are synonyms, look for instance:
https://link.springer.com/referenceworkentry/10.1007%2F978-1-4419-8071-7_189#:~:text=A%20surface%20plasmon%20polariton%20(SPP,electrons%20excited%20by%20electromagnetic%20radiation.
However, I think that Peter Y. Yu answer is more accurate, since you can excite a plasmon polariton with an electromagnetic (EM) wave or with a beam of electrons.
About the relation of plasmons with dipoles, when a metal or plasmonic material is exposed to an EM wave, the electric field polarizes the charges into the metal, causing a dipole (induced by the field). This is often represented with metal nanoparticles with sizes smaller or close to the wavelength, but it is also applicable to surfaces or interfaces, just that in these cases the wave propagation left an alternating charge separation along the surface.
Hope it helps.
Electromagnetic waves can excite an SPP, and an SPP can radiate, but this can only happen when the frequency of the two are the same (so that it keeps on happening as time changes); and when the phase progression along the surface is the same (so that it keeps on happening along a surface), that it what is meant by wave vector (k) being the same
Dear Ambar Shukla ,
The term “SPR: Surface plasmon resonance” can be used for two different phenomena: propagating plasmons in metallic thin films, and localized plasmons in nanostructures.
Propagating plasmons are called Surface Plasmon Polaritons (SPP) and you need some strategy (for instance, using a grating) to achieve the coupling, i.e. to increase the momentum.
On the other hand, the localized plasmons in metallic nanostructures are “localized surface plasmon resonances” (LSPR), which depend on the material (1), the dimensions (2) and the shape (3).
1) If you have nanospheres with the same diameter but some made of silver and others made of gold, the former would exhibit the LSPR peak at higher energy (lower wavelength).
2) If you have nanospheres made of the same material but some with diameter d1 and others with diameter d2, with d2>d1, the LSPR peak of d1 nanospheres would appear at higher energy (lower wavelength).
3) If you have a collection of identical aligned nanorods made of the same material, you would have two LSPR peaks depending on the light polarization: one along the rod axis and another along the perpendicular direction; the latter would appear at higher energy (lower wavelength).
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