If a particle has a surface plasmon resonance (SPR) intensity I1 excited by a laser intensity L1, it is reasonable to expect a SPR intensity of 0.5 I1 when the laser intensity is 0.5 L1?
Hi Anil! Thank you for your answer. Does that mean that the SPR intensity is always the same irrespective of the particle is in the beam waist (-> higher laser intensity) or not (-> lower laser intensity)?
I am a little bewildered by your "surface plasmon resonance intensity".
But, apart from the formulation, yes, this is linear science.
It is not an intensity based effect. Its not dependent on how many photons of light you shine on the particle.
If by "the SPR intensity", you mean the number of absorbed or scattered photons at resonance, then yes: doubling the incident light intensity will give you twice more absorbed or scattered photons. As Igor pointed out, that's linear physics.
But your formulation is somewhat ambiguous: most people measure SPR by absorption and the absorption spectrum is generally normalized using the formula given by Anil. In this case, the absorption value does not change when you increase the incident light intensity (but more photons will be absorbed, obviously).
Hi Thorsten,
In response to your original question: It depends on the irradiance. Noble metals such as silver have one of the largest nonlinear response found in nature. A search "nonlinear plasmonics" will lead you to a large body of literature exploring these effects. Most experiments with surface plasmons, however, are in the linear regime.
In response to your reply to Anil: I am not sure what you mean by intensity, since this is a term with different meanings in different countries as I have understood. Perhaps a less ambiguous term is Irradiance (power per unit area). This is called intensity by many people. At the beam waist the irradiance is higher than at the tails of the beam profile. It is ultimately the irradiance which matters for your problem. In other words, with the same incident laser power, you may observe a linear response if the beam area is large, or you may enter the non-linear regime if you tightly focus.
For practical purposes: If you are using ~mW powers or less, continuous wave, most likely you can igonore nonlinear effects.
I hope that helps.
To clarify the formulation: What I mean by intensity is the scattered light captured by a CCD camera. Thank your for you answer. You helped me a lot!
SPR depends upon the number of surface electrons and not depends on intensity.But the laser with particular wavelength which matches (resonant) nano particle's surface electrons enhances the band intensity bcoz of more number of surface electrons involved in reaction
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