We have seen the cloaking technology which covers another milestone towards achieving complete invisibility. The concept behind cloaking technology moves around Plasmons.
Now the question is - What are plasmons?
Just like photons and phonons which are quantization of light and mechanical vibrations respectively, the plasmons are quantization of plasma oscillations. So, Plasmon is a quantum of plasma oscillation or we can call it as collective oscillations of the free electron gas density.
Plasmons are the major contributor in deciding the optical properties of metals. Let us see HOW?
Plasmons decides the plasma frequency at the surface and light of frequency below this plasma frequency is reflected by the material, because the electrons in the metal screen the electric field of the light. All light waves with frequency more than plasma frequency will get transmitted and electrons wont be fast enough to respond and screen them. For most of the metals we see around, plasma frequency lies in the ultraviolet range which makes them shinny in the visible range as they reflects the light waves of visible range. Whereas metals like copper and gold have electronic interband transitions in the visible range, which makes them absorb specific light energies(lying in some specific color range). Due to this, they reflect some distinct color. Similarly in semiconductors, the valence electron plasma frequency is usually found to be in the deep ultraviolet, which is why they too are reflective.
Since plasmons are the major factor in deciding how objects yield different colors and shines, so the first step to achieve invisibility was to alter the plasma frequency in such a way that the visible light could easily get through the objects. This can be done if we can reduce the plasma frequency far below the visible light frequency. This is what cloaking technology is all about.
Now the question is - What are plasmons?
Just like photons and phonons which are quantization of light and mechanical vibrations respectively, the plasmons are quantization of plasma oscillations. So, Plasmon is a quantum of plasma oscillation or we can call it as collective oscillations of the free electron gas density.
Plasmons are the major contributor in deciding the optical properties of metals. Let us see HOW?Plasmons decides the plasma frequency at the surface and light of frequency below this plasma frequency is reflected by the material, because the electrons in the metal screen the electric field of the light. All light waves with frequency more than plasma frequency will get transmitted and electrons wont be fast enough to respond and screen them. For most of the metals we see around, plasma frequency lies in the ultraviolet range which makes them shinny in the visible range as they reflects the light waves of visible range. Whereas metals like copper and gold have electronic interband transitions in the visible range, which makes them absorb specific light energies(lying in some specific color range). Due to this, they reflect some distinct color. Similarly in semiconductors, the valence electron plasma frequency is usually found to be in the deep ultraviolet, which is why they too are reflective.
Since plasmons are the major factor in deciding how objects yield different colors and shines, so the first step to achieve invisibility was to alter the plasma frequency in such a way that the visible light could easily get through the objects. This can be done if we can reduce the plasma frequency far below the visible light frequency. This is what cloaking technology is all about.
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