Surface waves at a vacuum—plasma interface

It is emphasized that the dispersion relation for surface waves at a vacuum—plasma interface can be obtained by setting the reflexion coefficient to zero The relations for warm, collisional and hot, collisionless plasmas are derived in this way, and shown to be inagreement with previous results. The former relation is expressed explicitly as a cubic equation for y = 2c²k₁²/ω²_p, as a function of x = 2ω²/ω²_p - 1, where k₁ is thecomponent of the wave vector along the interface, a is the frequency and w the plasma frequency; and the nature of the three branches of the y(x) curve is analyzed in detail. The rotation of the vacuum wave vector as the frequency runs from 0 to ∞ is displayed, and it is established that one and only one branch corresponds, in the collisionlesscase, to pure surface waves.