In bulk diamond, a monotonic increase in ODMR contrast with laser power was observed, consistent with increasing NV -polarization levels [Fig. and]. Contrast was calculated as the mean value from the central resonances AL and AR. Interestingly, in NDs, a non-monotonic behavior was observed, as shown in Fig. . Up to 8.1 mW of laser power the ODMR contrast increases. At the highest power levels, the trend is the opposite, with a decrease in contrast systematically observed in different sample regions and for both ND sizes [Fig. ].