Plasma Optics (III)

First, we need to remember that the relation between \omega and f is linear, as described from \omega=2\pi f. We also know that f and \lambda are inversely proportional, which we can see from \lambda=\frac{c}{f}. This means that the behaviour of wavelength and frequency is opposite to each other. When the value of wavelength is high, we will get low value of frequency and vice versa.

The implications of dielectric function, from Plasma Optics (II)

diel func as plasma freq

are described as follows:

  • When incoming light interacting with the material has frequency lower than plasma frequency of the material, such that \omega<\omega_p, we will get negative value of the dielectric function. It implies the light is reflected from the surface of the material when the wavelength of the incident light is higher than the plasma wavelength of the material.
  • When incoming light interacting with the material has frequency higher than plasma frequency of the material, such that \omega>\omega_p, we will get positive value of the dielectric function. It implies the light is propagated through the surface of the material when the wavelength of the incident light is lower than the plasma wavelength of the material.

The above statements agree with the illustration given in the Figure 1 from Plasma Optics (I).

Figure 1. Visible wavelength, with group of alkali metal wavelength (155 - 362 nm)
Figure 1. Visible wavelength, with group of alkali metal wavelength (155 – 362 nm)

 

If the value of \omega_p=1 and the incoming light has \omega varying from 0 to 2, the response of the dielectric function is given in the figure 2.

Figure 2. The response of dielectric function to the omega of incoming light varying from 0 to 2
Figure 2. The response of dielectric function to the omega of incoming light varying from 0 to 2

How can negative dielectric function give rise to the reflected light? How can positive dielectric function give rise to the propagated light? We will try to find out in the next section.

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