Analysis of population dynamics and amplification of electron paramagnetic resonance signal of nitrogen-vacancy spins in diamond under laser illumination

Optical defects in diamond such as the negatively charged nitrogen vacancy centers are promising candidates for gain medium in the microwave region for continuous operation at room temperature owing to their ability of room temperature polarization and long spin lifetimes. Preferential polarization of its ground state, m_s = 0, sublevel with off-resonant laser illumination results in population inversion under suitable magnetic fields (>100mT). We will present our data on signal enhancement of continuous wave cavity detected EPR signals under low laser and microwave power conditions. We aim to discuss our quantitative analysis of this signal enhancement for the various EPR peaks in the spin system. The high field peak shows a sign flip verifies inversion which can be used to achieve low noise amplification and masing beyond a threshold pump power and cavity Q.