Ultrafast laser processing was shown recently to facilitate the generation of NV centres in diamond with spin coherence (300K) approaching 1 ms, a yield of about 40% and a positioning accuracy of better than one micrometre [1]. Here we report an adapted method for laser writing of individual colour centres which involves local laser annealing combined with feedback via a fluorescence monitor [2]. This method provides both improved positioning accuracy and near-unity yield for NV generation. We used a monocrystalline diamond sample with [Ns] ~2 ppm. Vacancies were generated with a single pulse from a 790 nm Ti:Sapphire laser. Local annealing was achieved with a 1 kHz stream of lower energy pulses. A fluorescence monitor allowed observation of the creation of NV centres in real time during annealing, such that deterministic writing was achieved by terminating processing when NV fluorescence was observed. Figure 1 shows an array of sites alongside a histogram of their autocorrelation functions; 24 of the sites contain single NV centres, representing a yield of 96%. The positions of the NVs were measured by recording fluorescence imagesand fitting analytic functions. Figure 2 shows the results revealing scatter of ~40 nm laterally and 200 nm axially, about a factor of five better than with a thermal anneal. The use of a pulsed laser to perform local annealing is the key to deterministic writing as it allows site-specific control over the process.
