Diffraction of the Millimeter Wave with Vortex Property by a Triangular Aperture

Recently, it has been shown that a radiation from a charged particle with spiral motion has vortex property. Various researches regarding a vortex beam has been carried out not only in the visible region but also in the various frequencies. Since an electron cyclotron motion is also spiral motion, an Electron Cyclotron Emission (ECE) should have vortex property. In order to experimentally demonstrate the vortex property of ECE, we have tried to generate the gyro-phase controlled multi-electron system, which can actively emit the ECE with vortex property. For this experiment, we developed the method to estimate the vortex property and to identify the Topological Charge (TC). This method is successfully checked by using the passively generated vortex beam from Gaussian beam in the millimeter wave region. The diffraction pattern by a triangular aperture of the passively generated vortex beam is observed. Since the diffraction pattern depends on the TC, we can identify the TC of the vortex beam. As a result, we were able to measure the characteristic diffraction patterns of millimeter wave vortex beam by a triangular aperture for the first time in the world. We will show the details of the experimental and calculation results.