Microwave Antenna Properties of an Optically Triggered Superconducting Ring

© 2019 IOP Publishing Ltd Printed in the UK We examine the microwave radiation emitted from inductively charged centimeter-scale YBCO (YBa2Cu3O7-δ) annular rings illuminated with a 45 fs, 790 nm laser pulse. The electromagnetic radiation from the rings shows the following behavior. (1) Radiation emitted perpendicular to the plane of the ring is polarized parallel to the plane of the ring and across the point of illumination. (2) The in-plane radiation pattern resembles that of a loop antenna with the orientation of the pattern determined by the location of the illumination point. (3) The dominant frequency of the emitted radiation shows an inverse dependence on the ring diameter. (4) The emitted energy is proportional to energy stored in the ring for a number of different geometries, with thinner films displaying a higher efficiency. Finally, (5) the emitted energy grows exponentially with small laser pulse energy values and approaches saturation for higher energies. These results indicate that optically induced electromagnetic radiation from superconducting structures holds promise for a versatile, compact, self-contained superconducting microwave emitter platform.