Development of the Grating Mirror for the High Power Transmission System and Its General Theory

Abstract

In the transmission system of the high power Electron Cyclotron Heating (ECH), many mirrors have been installed in the injection antenna section in particular. In some cases, it is difficult to design a normal mirror due to the restriction of the boundary condition. A grating mirror is one of the solutions in such cases. Moreover, controlled power splitting or combining at high power can be realized by a grating mirror. Diffraction angle, efficiency, and distortion/conversion of the polarization can be controlled by the grating shape design. In this study, we developed a grating mirror to efficiently separate the second harmonics component from the fundamental high power beam at 82.7 GHz and higher harmonics. The performance of this grating is confirmed experimentally for the use of vortex beam formation. During this development, the design procedure of a grating mirror is established and generalized to apply for various purposes.

Development of off-axis spiral phase mirrors for generating optical vortices in a range of millimeter waves

“…Some studies use a mirror design based on a constant phase at the mirror surface. 16,20 The shape of the mirror surface can be derived from the matching condition of the waist size and the wavefront condition based on elliptical Gaussian optics. In future work, it would be interesting to determine whether this design method can be expanded to LG beams and thereby mitigate the formation of asymmetric beams.…”

“…The machining goes in the negative z direction. For this simple design, z does not depend on the radius r. When a focusing effect is added to the mirror surface, 16 the surface height z becomes a function of r. The mirror surface of the CAD model consisted of a parametric surface z(r, ϕ) is given by Eq. (3) because z(r, ϕ) is a single-valued function.…”

“…13 The method used herein involves reflection at oblique angles of incidence, which should be compatible with high-power millimeterwave systems that commonly use focusing mirrors and grooved polarizers. [14][15][16] This paper describes the design, fabrication, and low-power test of off-axis spiral phase mirrors to generate optical vortices in a range of millimeter waves. impinges on the mirror surface at an oblique angle of incidence θ.…”

Cyclotron Emission with a Helical Wavefront from an Electron Accelerated by the Circularly Polarized Wave

“…The measurement system for millimeter-wave with helical wavefront was recently reported [9]. In order to demonstrate the ECE with helical wavefront, we designed and developed an experimental device that generates the ECE with helical wavefront in multi-electron system [10]. In this experiment, we attempt to control the rotation phase of electrons with cyclotron motion by externally applied circularly polarized wave so that the coherent radiation can be generated.…”

Diffraction Patterns of the Millimeter Wave with a Helical Wavefront by a Triangular Aperture

“…Since electron cyclotron motion is also a type of spiral motion, ECE should also have a helical wavefront. This experiment seeks to generate high power coherent ECE with a helical wavefront [16], and then identify the Topological Charge (TC). Here, TC is also called the orbital angular momentum quantum number, which is 2π times an integer (TC) from line integrating around the optical axis.…”