Fig. 4: Temporal and spectral characteristics of maser output.

a Temporal response of maser output power with a fixed LED pump duration of 200 µs (corresponding to a peak optical power of 75 W at the output of the PMMA waveguide), demonstrating immediate onset of maser oscillation. The maser exhibits persistent emission throughout the LED pump duration, with power variations attributable to Rabi oscillations. b Maser signal at different LED input pulse durations, exhibiting Rabi oscillations due to the coherent interaction between the microwave field and the pentacene triplet states. The oscillatory nature of the signal arises from population inversion dynamics, with variations in maser output power linked to pump duration and thermal effects. Compared to (a), the slightly reduced maser output at 200 µs results from thermal variations induced by the gradual buildup of pump energy over time. c Output power of the LED-maser at various resonant frequencies, with the highest power observed at 1.4493 GHz. d Maser peak output power as a function of LED-LC pump energy, showing threshold behaviour. The data is limited to the low-energy regime (up to 1 mJ) to highlight the onset of masing. Full-range output dynamics are presented in (b).