Transversal plasma resonance in a nonmagnetized plasma and possibilities   of practical employment of it
  It is shown that in a nonmagnetized plasma, beside the longitudinal Langmuir resonance, there may also exist the transversal resonance. Both these resonance kinds are degenerated. Employment of the transversal resonance makes it possible to design resonators and filters, as well as powerful single-frequency lasers operating on the basis of collective oscillations of plasma. 
F.F.Mende