Iridium–Gold Bilayer Optical Transition Edge Sensor

Recently, there is a demand for a single-photon detector in the mid-infrared wavelength. For that reason, we fabricated an optical transition edge sensor with an Ir–Au bilayer and demonstrated the behavior of this device. There is a possibility to improve the energy resolution of this device by lowering superconducting transition temperature and reducing heat capacity. In addition to this, because of the chemical stability of Iridium, the Iridium-based devices are easy to fabricate, and they tend to have long-term stability. We also etched a silicon wafer to match the inner diameter of an optical fiber sleeve. This process helped us improve the accuracy of alignment with the core of optical fiber and a sensitive area of this optical transition edge sensor. Consequently, we found that the superconducting transition temperature was estimated to be approximately 175 mK and developed an Ir–Au optical transition edge microcalorimeter with an energy resolution of 0.68 eV full-width at half-maximum for the pulse laser at 850 nm. This result will contribute to the measurement of photons.