Why is plasma frequency in ev and not hz

[OrigamiNinja]

Why is the plasma frequency and the relaxation frequency expressed in eV instead of Hz? eV is a measurement of energy, not frequency.

What is the plasma frequency, relaxation requency and Debe length, and how are they all related?

Thanks,

Ninja

 

[G01]

eV can also be used as a unit of electromagnetic frequency. Remember the photoelectric effect result:

E=\hbar\omega=hf

Thus, a E/M wave of frequency \omega can just as easily be labeled by it's photon energy. In some cases this is preferred, just because the numbers are easier to work with. For example,

A light wave of frequency, 4X10^14Hz has a photon energy of ~1.65eV. I think most people would agree that the second number is less cumbersome to work with.

Experimentally, it's also useful to express frequency in eV, especially if you are studying electromagnetic properties of materials. Many electronic effects in materials (usually labeled by energy differences between bands, etc.) cause noticeable effects in the frequency spectrum of the materials dielectric constant or index of refraction. Thus, it makes sense to leave frequency in units of eV, if you are looking for such effects.

When given a frequency of light in eV, you can convert back to Hz by dividing by Planck's constant.

The Plasma frequency is a characteristic frequency for plasma systems or a system, like metals, where the charge carriers can be treated as a plasma. Basically, if you treat the electrons in a metal as being SHO oscillators, with the Coulomb force as the restoring force, and drive the electrons with an external E-Field, the resonance frequency you will obtain will be the plasma frequency.

For a metal, light with frequency less than the plasma frequency is mostly reflected. The transmitted light is screened and drops exponentially in strength inside the material. For light above the plasma frequency, the charge carriers cannot respond quickly enough to screen the field, and the light is mostly transmitted.

The Debye length is the characteristic length scale over which charge carriers in a material screen the electric field to 1/e of it's initial value.

 

[OrigamiNinja]

that was a great answer.

see if you can answer my question farther down the 'quantum physics' thread list, which involves more of the core of what I'm trying to do.

the thread is:
"using the drude equation to find the dielectric function"

Thanks for the response,

Ninja

 

[OrigamiNinja]

also, nice avatar.