Propagation of Electromagnetic Waves in Plasma

Electromagnetic wave propagation in plasma is described by the conventional wave equations  

Plasma peculiarities are related to the complex dielectric permittivity e (3.283, 3.284). The dispersion equationfor electromagnetic wave propagation in a dielectric medium (where c is the speed of light), 

Parameter n is the refractive index of the electromagnetic wave phase velocity is V — j — and the wavelength is A = Xo/n (where ko corresponds to vacuum). The wave number k characterizes the attenuation of electromagnetic wave in plasma that is, the wave amplitude decreases e times over the length kolln. Relations between refractive index and attenuation with high-frequency dielectric permittivity and conductivity are 

Solving this system of equations results in an explicit expression for the attenuation coefficient  

Attenuation of the electromagnetic wave is determined by the plasma conductivity if BraSoco, the electromagnetic field damping can be neglected. The explicit expression for the refractive index is 

---

Transverse electromagnetic waves propagate in plasmas if their frequency is greater than the plasma frequency. For a given angular frequency, CO, there is a critical density, above which waves do not penetrate a plasma. The propagation of electromagnetic waves in plasmas has many uses, especially as a probe of plasma conditions. 

V.L. Ginzburg, Propagation of Electromagnetic Waves in Plasma , Gordon Breach, NY (1961) 3) DJ. Rose M. Clark Jr,... 

Ginzburg, V. L. (1967). The Propagation of Electromagnetic Waves in Plasma. Nauka, Moscow English translation (1970). Pergamon, Oxford. 

Plasma electrodynamics is a very important and widespread branch of plasma physics that covers in particular such topics as plasma sheaths, plasma oscillations and waves, propagation of electromagnetic waves in plasma, plasma instabilities, magneto-hydrodynamics of plasma, and collective and non-linear plasma phenomena. Only the most general aspects of plasma electrodynamics relevant to plasma chemistry will be discussed here. Details on the subject can be found in particular, in books of Kadomtsev (1976), Ginzburg (1960), Boyd and Sanderson (2003), and Fridman and Kennedy (2004). 

High-frequency plasma conductivity and dielectric permittivity are important concepts to analyze the propagation of electromagnetic waves in plasma. One-dimensional electron motion in the electric field E = Eq cos cot = Re Eoe ) can be described by the equation ... 

This frequency is a measure of the vibration rate of the electrons relative to the ions which are considered stationary. Eor tme plasma behavior, plasma frequency, COp, must exceed the particle-coUision rate, This plays a central role in the interactions of electromagnetic waves with plasmas. The frequencies of electron plasma waves depend on the plasma frequency and the thermal electron velocity. They propagate in plasmas because the presence of the plasma oscillation at any one point is communicated to nearby regions by the thermal motion. The frequencies of ion plasma waves, also called ion acoustic or plasma sound waves, depend on the electron and ion temperatures as well as on the ion mass. Both electron and ion waves, ie, electrostatic waves, are longitudinal in nature that is, they consist of compressions and rarefactions (areas of lower density, eg, the area between two compression waves) along the direction of motion. 

The study of the ionosphere has largely been performed by observation of the properties of radio wave propagation through this medium. In this work we will not attempt to present an exhaustive study of the interaction of electromagnetic waves and a weakly ionized plasma, nor... 

In the previous sections we have considered electromagnetic waves which propagate in an homogeneous material or which are reflected at an interface. A different type of electromagnetic waves which are important in metal optics are the delocalized surface plasmon resonances or surface plasmon polaritons (SPPs), which consist in propagating, dispersive electromagnetic waves coupled to the electron plasma of a metal at a dielectric interface, but evanescently confined in the perpendicular direction [7,12,13]. 

At high frequencies co Ven), the absorption coefficient is proportional to the square of wavelength (/u., a co a therefore, short electromagnetic waves propagate in plasma more readily. 

Many biosensors are based on surface plasmon resonance. In this case, the excitation by light of surface plasmons, surface electromagnetic waves that propagate parallel along a metal/dielectric interface, results on oscillations in the wave that are very sensitive to the adsorption of molecules to the metal surface. Plasma-polymerized nanocoatings might be applied to immobilize such biomolecules. 

Therefore, if e > 0, i is real, and the medium is transparent the electromagnetic wave propagates without any absorption. After Eq. (13.53), this is the case when to > tOp. For the high carrier densities met in metals, the plasma frequency is in the visible of near ultraviolet, which explains the transparency of alkali metals (Li, K,) in the UV. On the other hand, if to < tOpEq. (13.53) shows that is real but negative so that h (co) and q are pure imaginary. In that case, is an evanescent wave that is just needed to fulfill the boundary conditions (continuity of the fields) at the surface when the sample is illuminated by a beam at this frequency the light cannot penetrate in the sample, and is totally reflected at the surface. That is why well-polished metallic surfaces are mirrors. 

---