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Thanks to its high electrical conductivity, a graphene plane presents a good shielding efficiency against GHz electromagnetic radiations. Several graphene planes separated by thin polymer spacers add their conductivities arithmetically, because each of them conserves the intrinsic properties of isolated graphene. Maximum absorption of radiations for frequency around 30 GHz is achieved with six separated graphene planes, which is the optimum number. This remarkable result is demonstrated experimentally from electromagnetic measurements performed in the Ka band on a series of multilayers obtained by piling 1, 2, 3 … graphene/PMMA units on a silica substrate. Theoretical calculations convincingly explain the observed absorption and transmission data in the GHz domain. It is concluded that graphene/PMMA multilayers can be used as an efficient optically transparent and flexible shielding media.

We demonstrate theoretically the parametric oscillator behavior of a two-level quantum system with broken inversion symmetry exposed to a strong electromagnetic field. A multitude of resonance frequencies and additional harmonics in the scattered light spectrum as well as an altered Rabi frequency are predicted to be inherent to such systems. In particular, dipole radiation at the Rabi frequency appears to be possible. Since the Rabi frequency is controlled by the strength of the coupling electromagnetic field, the effect can serve for the frequency-tuned parametric amplification and generation of electromagnetic waves. Manifestation of the effect is discussed for III-nitride quantum dots with strong built-in electric field breaking the inversion symmetry. Terahertz emission from arrays of such quantum dots is shown to be experimentally observable.

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