A new type of coherent electromagnetic radiation source based on interference effect between forward and backward waves in an active metamaterial slab

In this paper, we shall show first that both reflection and transmission can be significantly amplified when a beam of electromagnetic wave is normally incident into an active (even lossy) metamaterial slab with near-zero-real-part-of-impedance, which is attributed to effect of interference between forward and backward waves in the slab. Then we demonstrate that extended steady electromagnetic waves can be achieved using a double-slab structure, which may be applied to generate coherent electromagnetic wave with very narrow frequency band and very low divergence angle. This work provides feasible scheme to construct a new type of source of coherent electromagnetic radiation based on new physical mechanism.