Formation process of nitrogen-vacancy centers in diamonds by sub-10 femtosecond laser pulses

Nitrogen-vacancy (NV) centers in diamonds have attracted attention for their potential applications in quantum sensing and optical quantum computing. Recently, intense femtosecond (fs) laser irradiation has been proposed as a high spatial-resolution method for generating NV centers. However, it often occurs undesirable graphitization of diamond. We demonstrated the formation of NV centers in diamond surfaces using sub-10 fs laser pulses and investigated their formation process. In the experiment, fs laser pulses with a wavelength of 650–1000 nm, a repetition rate of 80 MHz, and a pulse duration of 7 fs were focused onto single-crystal CVD diamond surfaces and scanned over a 5 μm region. The photoluminescence (PL) intensity in a wavelength of 579–750 nm with 561-nm excitation increased approximately threefold compared to non-irradiated areas, indicating the formation of NV centers. No signals indicating sp2 bonding structures, i.e., graphitization, were observed in the PL spectra. By changing the peak power density of the fs pulses at a peak intensity of 8.0–11.0 TW/cm2, the PL intensity peaked at 10.5 TW/cm2. These results demonstrated that 7-fs laser pulses enabled efficient formation of NV centers in diamonds, while suppressing graphitization.