The time-resolution of the spectrometer is c.a. 100 ns, as shown in Fig. . A laser de-polarizer (SIGMA KOKI, DEQ1N) was placed between the laser exit and the microwave cavity for the TREPR experiments. The samples synthesized by the Richert group were dissolved with a concentration of 41.3 µM and degassed by the freeze-pump-thaw cycles using the vacuum line. A modified flex line dielectric resonator (Bruker, ER4118X-MS5) was used for the room-temperature TREPR.