Cherenkov maser based on a twodimensional periodic lattice

The recent results from the study of periodic structures have made a significant impact in many branches of physics and led to a number of breakthroughs in photonics, optics, electronics and communications. We discuss the concept1 and the results of studies of a Cherenkov maser based on a 2D lattice. The maser considered is capable of producing high-power output radiation in the high-GHz - low-THz frequency range, which is very attractive for a number of applications. Although the ability to generate high-power output radiation is necessary for remote sensing, imaging, biological and medical science (for instance to reduce the exposure time during large area mapping), masers that are capable of producing the required output power in the high GHz to low THz frequency range are still not available. One notes that, the Fresnel number of a typical maser based on a closed cavity and driven by a mildly-relativistic electron beam (Lorentz factor γ ≥ 1.2) is usually much smaller than 1, limiting the maser's interaction region aperture, while keeping the interaction length large as compared with the operating wavelength, which acts to maintain single mode steady state lasing. Problems arise as one seeks to reduce the operating wavelength resulting in a reduction in the transverse aperture which leads to lower output power, high energy losses and maser miniaturization. To maintain the coherence of the radiation the use of a twodimensional periodic lattice to form the interaction region is considered. We present the results of study of a Cherenkov maser based on a 2D periodic lattice used to achieve the desired level of output power while still maintaining the coherence of the output radiation. In this case the large interaction region formed by the periodic lattice allows a moderate power density inside the beam-wave interaction space whilst simultaneously avoiding the formation of electron beam instabilities associated with high beam charge density. We demonstrate that the structure also provides effective mode selection over the azimuthal and radial wave numbers. This ensures a single mode, steady state operation of the maser with an interaction space defined by a large diameter (a/λ ∼7) 2D periodic cylindrical structure. The results of the studies of the operation of a Cherenkov maser based on a 2D periodic lattice are presented and we show that a single mode, steady state operation at a frequency of ∼90GHz was achieved. The conditions required to observe effective interaction between the electron beam and an EM wave are also discussed.