ESR with Radiation Damping*

We present an expansion of coherent control in the field of Electron Spin Resonance (ESR) for long T1 samples, achieved through the engineering of radiation damping. This advance enables efficient spectroscopy in cases with long T1 relaxation times. Our exploration of ESR dynamics involves the utilization of high quality factor, small magnetic mode volume superconducting resonators (Nb or YBCO). Our system is capable of operating at 0.45 K using a custom He-3 refrigerator. We demonstrate long-lived transient response induced by radiation damping, achieved through appropriate design of spin-cavity system parameters. This study is a step toward controlling cavity-mediated spin-spin interactions.