How the light is getting additional momentum if it is passing through some array of periodic nanostructures?
How the light is getting an additional momentum (2pi/G) if it is passing through an periodic array of nanostuctures or nano-holes? which physical quantity is supplying this additional momenta...?? and in that case what is the physical significance of "G" ??
It might not be helpful to think of the stratified medium giving the light additional momentum, but rather think of it as selecting the momentum states of the light that can propagate through it.
Dear dr. Sivadasan,
I fully agree with dr. Allsopp's answer insofar as the periodic array of nanostructures is considered a passive device, i.e. somewhat like a grating.
However, for example in the book: “Plasmonic nanoguides and circuits”
https://books.google.co.uk/books?id=NwNWSSfEbSQC&pg=PA420&lpg=PA420&dq=light+gets+additional+momentum+g&source=bl&ots=1k46UnMA2t&sig=E8R8YoF8FhuGrE4dLLAQFCqPZZY&hl=en&sa=X&ved=0ahUKEwiAwfSHhLjKAhVDdA8KHag2D7sQ6AEILDAD#v=onepage&q=light%20gets%20additional%20momentum%20g&f=false
it is stated: “This additional “momentum kick” enables the coupling of normally incident light (with no in-plane momentum) to SPPs and the condition βsp = 2π/G is satisfied.” (on p. 420) in a context in which I would not exclude the presence of an active medium. Perhaps using G for a "momentum kick" is not the best choice.
Dr Vesely is correct: The Bloch condition partitions momentum (i.e. wave vector) between that associated with plane wave-like propagation [i.e. exp(-ikx) behaviour] through the effective medium formed by the photonic crystal and the momentum associated with a more slowly varying envelope [i.e exp(-iGx) behaviour] that has follows the periodic variation on refractive index where the free space propagation vector k' = vector sum of k and G, the latter being vector quantities. In other words no momentum is lost of gained by light propagation through a photonic crystal.
dear Dr. D.W.E. Allsopp,
Thank you for reply ...and I am agreeing to your statements...but still I am not clearly understood that, How the patterned arrangement and its periodicity will influence the light, there is no extra agency ( like phonons) to supply some additional wave vector to it....and it is also reported that by tuning the periodicity we can tune the wavelength of light.... How it is happening exactly?
No extra agency is needed. The momentum change comes from the light-wave undergoing periodic elastic scattering with the same periodicity of the refractive index variation. A fundamental review of the process can be found on Wikipedia under "Diffraction".
To try and explain the difference between passive and active devices I would suggest to compare the behavior of a grating with that of a frequency mixer.
Suppose that there is a monochromatic light source. A grating will pass the zero-order mode as well as higher orders (+1, -1, …). One could interpret the higher orders as if they were “shifted” copies of the zero-order light (if the light of the source is not monochromatic, higher orders show dispersion.)
The performance of a mixer is apparently analogous. However, the higher orders are “produced” by the mixer itself. Thus additional frequencies may appear, which belong neither to the source, nor to the mixer.
I hope that my comment can be useful.
As for my cosmic and atomic theory, where all the forces and elements are similar as in the microcosms as well in the macrocosms, this is due to the effect of gravitational acceleration when a particle (or Astros at stars level) passes through the gravity fields of a next major particle or Astros.
As example, we could put the pass of a rocket next to a great gravity field on any planet as could Jupiter.
In these cases if photons pass next to ordered atoms, and these photons are deviated orderly, they can be accelerate by the gravity and magnetic fields of those atoms.
Thank you.
- Badges
- Science topic
- Similar topics
- Physics