From the various discussions on the difference between surface plasmon resonance (SPR) and surface plasmon polariton (SPP) I got the impression that there is some misunderstanding of what are SPR and SPP.

It is important to understand what are plasmons. As pointed out by some one that plasmons are oscillations of the electrons in a plasma. Such oscillations are traveling waves with well defined frequency and wave vector. However, it should be noted that these plasma waves are longitudinal waves, ie the displacement of the electrons (relative to a uniform positive background formed by positive ion) are parallel to the direction of propagation of the wave. These plasma waves can exist in 2D (although the dispersion of the wave is different from that of 3D plasmon) or at the interface between two media (leading to surface plasmon). When plasmons are excited one creates plasmon resonances. The important thing to note now is that plasmons are longitudinal waves so they cannot be excited by a transverse wave like an electromagnetic wave. Usually the most effective way to excite a plasmon is to use electrons. For example, an electron beam passing through a thin metal foil will lose energy when it excites a plasmon. This loss in energy is exhibited by a peak in the electron energy loss spectrum (commonly known as EELS).

Having said that plasmons (including SPR) cannot be excited by photons, then one can ask why there are SPP? A polariton, by definition, is a coupled dipole-electromagnetic wave. The best known example of polariton is the phonon-polariton in ionic crystals first proposed by the famous Chinese solid-state physicist: Kun HUANG in his classic paper:

K. Huang, “Lattice Vi brations and Optical Waves in Ionic Crystals”, Nature 16, 7779 (1951).

This paper pointed out that the transverse optical (TO) phonon will couple to photon when their wave vectors and frequencies are the same. This coupling modifies the dispersions of both the optical phonon and photon. The resultant coupled TO phonon-photon mode was labeled by Huang as the polariton. The longitudinal optical (LO) phonon cannot couple to the photon since it is a longitudinal wave. This is the reason why plasmons in 3D cannot form polaritons. In case of an interface, the situation is different because a photon can be incident on the interface at an angle. For a photon polarized in the plane of incidence (p-polarized) the polarization can be decomposed into two components with one perpendicular to the interface and the other parallel to the interface. The parallel component can then excite a surface plasmon because this component is now a longitudinal wave. To form a SPP, the photon and SPR must have the same frequency and wave vector. This means that the component of the photon wave vector parallel to the interface has to be equal to that of the SPR. Thus to observe a SPP one has to monitor absorption of a incident EM wave of constant frequency as a function of the angle of incidence on the interface (by changing the angle of incidence one can tune the component of the photon wave vector parallel to the interface). The presence of a peak in the absorption will indicate the excitation of a SPP. By varying the incident photon frequency and determining the angle of incidence for observing the SPP (hence the wave vector of the SPP) one can determine the dispersion of the SPP.

Yes obviously the two are quite different ........polariton and plasmon are two particles like the photon while surface plasmon resonance is a physical process....In one hand there are particles and the other hand a process is there...No doubt these quantisation particles are involved there in the resonance process but they are never same...they are quite different

In my novice understanding (could an expert confirm), the distinction is:

plasmon - quantization of plasma/electron oscillations

polariton - photon-induced plasmon (ie plasmon and photon coupled)

surface resonance - propogation of plasmon/polariton collectively along a surface

Adam, a lot of people mix the two up. If you look up a plasmon in your E&M book you will find it has specific properties. I have found people use surface plasmons when referring to nanoparticles because the excitation cannot propagate away from the nanoparticle. A surface plasmon polariton can propagate from its point of origin along the surface. Consequently, it will experience dispersion. This is a very crude explanation. Good question.

I quote from an article by Jean-Jaccques Greffet " From the point of view of electrodynamics, suface plamons are a particular case of surface wave. From the point of view of Optics, surface plasmons are modes of an interface. From the pony of view of solid state physics, a plasmon is a collective oscillation of electrons."

In case of noble metal nanoparticles, when an EM radiation is incident on the nanoparticle, its surface electron cloud oscillates coherently relative to a lattice of positive ions, due to the alternating field of the incident radiation. The coherent oscillation leads to displacement of the electron cloud from the nuclei, thus giving rise to a surface charge distribution. A coulombic attraction resulting from the displacement induces a restoring force, characterized by oscillation frequencies of the electron cloud with respect to the positive background. Each such collective oscillation associated to different surface charge distribution is known as Surface Plasmon Resonance (SPR).

Localized surface plasmons LSP, are non propagating excitations of the conduction electrons coupled to the electromagnetic field. For a spherical nanoparticle, the curved surface of the nanoparticle exerts a restoring force on the electrons to result in a resonance. This resonance is called a localized surface Plasmon resonance or in short localized Plasmon resonance. It is concluded that these modes arise naturally from scattering problem of the small, subwavelength conductive nanoparticles in the oscillating EM field. This kind of resonance can be excited by direct light illumination, which is a consequence of the curved surface of the metal nanoparticles. This resonance for gold and silver nanoparticles occurs in the visible region of the electromagnetic spectrum. As a consequence, we are able to see the bright colors exhibited by particles, both in transmitted and reflected light, due to resonantly enhanced absorption and scattering.

Surface Plasmon Polaritons (SPP) are electromagnetic excitations, which propagate at the interface between a dielectric and a conductor, and are evanescently confined in the perpendicular direction to the propagation. These arise via coupling of the electromagnetic field to oscillations of the conductor’s electron plasma. They are characterized in terms of dispersion and their spatial profile.

Many thanks for all especially for Santa Chawla . I really start now to understand Surface Plasmon more accurately.

A comprehensive explanation was made by Santa Chawla, I support that,

I am still confused about polaritons...

A gold nanoparticle is an interface between a dielectric and conductor, so is it wrong to consider these interactions as localized plasmon polaritons? Are they not polaritons because polaritons must be able to propogate freely, like they would along a surface?

In simple terms, are there instances where we can have plasmon resonances without plasmon polaritons, or are they just terms applied to similar aspects of the same phenomena?

what I got from this, SPR ( oscillation of charges on the surface). SPP ( the full operation start from excitation ,propagation and confining>>all these come from coupling)

Surface Plasmon Polaritons are surface charge density waves which can propagate along metal-dielectric inteface.

In a metallic nanoparticle, opposite to the propagating SPPs along a flat surface, the confined geometrical boundaries sustain a localized oscillation of the surface charge density which is usually called localized surface plasmon.

A very good book in this topic is recent one(2012) in Springer series in optical sciences "Plasmonics From basics to Advanced Topics", edited by Stefan Enoch and Nicholas Bonod.

SPPs refer to a coupled electromagnetic-electron waves along the metal-dielectric interface. And SPR is a physical resonance state, which is established when the frequency of incident photons matches the natural frequency of surface electrons.

It is not necessary that frequency of incident photons to match with frequency of SPR. THERE ARE PLENTY OF REPORTS OF off RESONANCE EXCITATION.

Surface plasmon polariton is an electromagnetic wave. Surface plasmon resonance is phenomenon when exciting electromagnetic wave is coupling with structure supporting plasmon modes. Resonance conditions will be defined by the structure. Structures could be different. it could be a single metal film, multilayer structure or nanoparticle.

There is no difference in the physics. You might use "polariton" to emphasize the phenomenon itself when light couples to a mode confined to a metal-dielectric interface. The "resonance" implies that you have found the right incident wavevector and frequency for excitation to occur. SPR is also the name of the commercial sensor technology.

I agree with Andreas. These are just slightly different words describing the same phenomenon. Surface plasmon (without "polariton"), or "surface plasma wave" are also good enough.

About the surface plasmon resonance, I agree with IIdar. It is the physical phenomenon confined by particular structure, like metal film, muti-dimensions structure and nanoparticles. For the surface plasmon polariton, it is the polarization response of electrons in metal based on "surface plasmon (like photons or phonons)".

I used both "surface plasmon" and "surface plasmon-polariton" having in mind the same thing. However, the last one is probably more accurate. Otherwise it can be confused with the term existing in plasma physics; I had such problem. Word "polariton" shows that we are dealing with optical frequencies.

One can make the differentiation by calling localized surface plasmon (LSP) for localized oscillations and surface plasmon Polariton (SPP) for propagating waves TO DISTINGUISH THE DIFFERENT NATURE. Else there is confusion in reader's mind about the physical process being described.

From the various discussions on the difference between surface plasmon resonance (SPR) and surface plasmon polariton (SPP) I got the impression that there is some misunderstanding of what are SPR and SPP.

It is important to understand what are plasmons. As pointed out by some one that plasmons are oscillations of the electrons in a plasma. Such oscillations are traveling waves with well defined frequency and wave vector. However, it should be noted that these plasma waves are longitudinal waves, ie the displacement of the electrons (relative to a uniform positive background formed by positive ion) are parallel to the direction of propagation of the wave. These plasma waves can exist in 2D (although the dispersion of the wave is different from that of 3D plasmon) or at the interface between two media (leading to surface plasmon). When plasmons are excited one creates plasmon resonances. The important thing to note now is that plasmons are longitudinal waves so they cannot be excited by a transverse wave like an electromagnetic wave. Usually the most effective way to excite a plasmon is to use electrons. For example, an electron beam passing through a thin metal foil will lose energy when it excites a plasmon. This loss in energy is exhibited by a peak in the electron energy loss spectrum (commonly known as EELS).

Having said that plasmons (including SPR) cannot be excited by photons, then one can ask why there are SPP? A polariton, by definition, is a coupled dipole-electromagnetic wave. The best known example of polariton is the phonon-polariton in ionic crystals first proposed by the famous Chinese solid-state physicist: Kun HUANG in his classic paper:

K. Huang, “Lattice Vi brations and Optical Waves in Ionic Crystals”, Nature 16, 7779 (1951).

This paper pointed out that the transverse optical (TO) phonon will couple to photon when their wave vectors and frequencies are the same. This coupling modifies the dispersions of both the optical phonon and photon. The resultant coupled TO phonon-photon mode was labeled by Huang as the polariton. The longitudinal optical (LO) phonon cannot couple to the photon since it is a longitudinal wave. This is the reason why plasmons in 3D cannot form polaritons. In case of an interface, the situation is different because a photon can be incident on the interface at an angle. For a photon polarized in the plane of incidence (p-polarized) the polarization can be decomposed into two components with one perpendicular to the interface and the other parallel to the interface. The parallel component can then excite a surface plasmon because this component is now a longitudinal wave. To form a SPP, the photon and SPR must have the same frequency and wave vector. This means that the component of the photon wave vector parallel to the interface has to be equal to that of the SPR. Thus to observe a SPP one has to monitor absorption of a incident EM wave of constant frequency as a function of the angle of incidence on the interface (by changing the angle of incidence one can tune the component of the photon wave vector parallel to the interface). The presence of a peak in the absorption will indicate the excitation of a SPP. By varying the incident photon frequency and determining the angle of incidence for observing the SPP (hence the wave vector of the SPP) one can determine the dispersion of the SPP.

Speaking of localized surface plasmons. In principle they can be represented as a superposition of propagating SPP (just like standing waves). So the difference between SPP and LSP seems to be very vague in this respect.

Surface Plasmon Polaritons are the coupled oscillations of electromagnetic waves with the electrons at the metal dielectric interface. On the other hand Surface Plasmon Resonance is the phenomenon of coupling incident energy to the oscillating free electrons at the metal dielectric interface.

"For a photon polarized in the plane of incidence (p-polarized) the polarization can be decomposed into two components with one perpendicular to the interface and the other parallel to the interface. The parallel component can then excite a surface plasmon because this component is now a longitudinal wave."

I dont understand why  parallel component is longitudinal component? 

and the perpendicular component isn't a longitudinal component for the perpendicular direction so why it can't excite the bulk plasmons?

@Dmitry Lev , if you take the components of the Electric field of a P polarized light along the plane you will find it is pointing towards the propagation direction. 

Of course, the electric field is transverse to the propagation direction for an EM field, however, with respect to a plane that lies at an angle with respect to the E field (and the k vector) you will find that the component of the k vector and the component of the E field (for P pol. light) coincide. 

SPR means electromagnetic waves due to the electron oscillation

SPP means plasmon carrying photon resulting from the coupling between the plasmon and incident ligth 

@ Peter Y. Yu 

Because the dispersion of surface plasmon polariton is located outside the light cone, incident light cannot excite them even at interface, so the momentum matching is satisfied by other means, as you know, like gratings or Kretschmann configuration. One needs a mediator to match the momentum of light and plasmons. It is not quite true that longitudinal plasmons do not couple with photons. If one places an emitter inside a metal, photon-longitudinal plasmon coupling will take place.

As for electrons, it is also the evanescent field of the electron at motion (Coulomb field) which excites the longitudinal plasmons, not the electron as a particle itself. This also happens because the electron penetrates inside the metal. You cannot excite the bulk plasmons with electrons which are not traversing the metal.

The following website is very useful to understand the difference between LSPR and SPR

https://nicoyalife.com/technology/surface-plasmon-resonance/localized-surface-plasmon-resonance-theory/

Surface plasmon polariton is fundamental thing whereas surface plasmon resonance is effect observed due to presence of fundamental thing. SPP and SPR is not same. It is cause and effect respectively.

read the attached article:

Homola, J., Yee, S.S. and Gauglitz, G., 1999. Surface plasmon resonance sensors. Sensors and Actuators B: Chemical, 54(1-2), pp.3-15.

Many excellent answers are already made available here. Thanks every one. Below is my two cents (collected from various internet sources) as:

Surface plasmon polaritons (SPPs) are electromagnetic (EM) waves. They travel along an interface between two materials that have opposite value of real part of permittivity. The EM wave includes charge motion in the metal which is called surface plasmon and EM wave in the dielectric medium which is called "polariton." Surface plasmon resonance (SPR) is the resonant oscillation of conduction electrons activated by the incident EM waves. This phenomenon occurs at the interface between negative and positive permittivity material.

Dear Conrad Rizal,

Thanks a lot for your answer, but how we can connect that to the Evanescent waves please? Is there any link?

Cheers.

The SPPs propagate along the interface and exponentially decay perpendicular to it, that's why they are evanescent waves (in either way, the wavenumber in the direction normal to the interface becomes imaginary and hence the waves do not propagate in this direction)

After so many fruitful discussions it can be said that Localized surface plasmon resonance (LSPR) occurs due to the collective oscillation of free electron in the nanoparticles.It can not propagate. However Surface plasmon polaritons (SPP) are electromagnetic excitation that propagate at the interface between dielectric and the conducting layers.

I agree. LSPR is the normal (stationary) mode of the free electron oscillation and occurs in a single frequency w_p (plasma frequency). On the other hand, SPP are propagating modes (quasi-particles) arose from the coupling between plasmon and light and occurs in a frequency range w_sp which is always smaller that w_p (i.e. wsp < wp).

You can find details in this Chapter Chapter Graphene and Active Metamaterials: Theoretical Methods and P...