Fig show the ODMR spectra of the bulk diamond and NDs at different laser powers (from 1 to 30.5 mW) at constant MW power of 15 dBm. The ODMR spectra show the NV -central lines (AL and AR) and two side bands (BL and BR), the latter related to the hyperfine interaction between the NV -spins and the 13 C nuclear spins . The 13 C sidebands are separated from each other by ~130 MHz, consistently with previously reported values . For all samples, the linewidth of the resonance bands decreases with laser power, in agreement with the linenarrowing effect described by Jensen et al. . Alongside with the increase in signal-to-noise (SNR) ratio, this phenomenon improves resolution of the NV -strain-split doublet (central dips AL and AR). We did not observe any detectable temperature effect on the position of the ODMR resonance that may be caused by absorption of MW or laser power .