Hello.
I've read some article that the inverse bremsstrahlung is the process that a free electron absorbs a photon while it collides with an ion, so it is 3-body process.
But I don't know how it is physically explanined. Why the electron that is in collision with the ion can absorb the photon?
And I would like to know the relationship between the laser energy and the plasma electron density. I've also read the following relations.
1. If plasma angular frequency wp < laser angular frequency w : the plasma is transparent for the laser.
2. If wp = w : the plasma becomes a perfect mirror.
3. If wp > w : the plasma becomes a good laser absorber.
I can understand the 1st case as it is easily proved in a undergraduate level plasma physics course. 2nd case...is what I may accept.. But 3rd case...how can it is physically explained?
Thanks for reading this and I look forward to get any response.
The third points depends on the cross section of the process that increases with the frequency, The optical properties of a material, as well as that of a plasma depends on the dielectric constant that is a complex quantity, where the imaginary part is the conductivity of the material. Analyzing the response of the plasma to the frequency, Higher the conductivity at a given frequency, higher the reflectivity. All the material have response frequency that for a plasma in wp. The conductivity has a bell shape as a function of the frequency, with a maximum around wp. Reverse bremsstrahlung happens when the plasma is transparent, and because its cross section grows with the frequency, it explains the third point.
Thank you for your explanation, Dr. Colonna.
I have an additional question, why the plasma should be transparent to generate the inverse-bremsstrahlung process? I think plasma must be opaque rather than transparent to satisfy the physics according to the critical angular frequency of plasma relating to a complex index of refraction.
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