Femtosecond Direct Laser Writing for Diamond NV Centers Placement

The integration of devices for applications in photonics and quantum information technologies requires the development of platforms combining basic elements, such as resonators and waveguides. One promising solid-state optically active systems currently studied for such applications is the nitrogen-vacancy (NV) center in diamond, which is usually produced by irradiating diamond with beams of electrons or nitrogen ions. NV centers can be optically initialized and read out, present long coherence times at room temperature and allows creating protocols to manipulate its spin-state by combining optical and magnetic methods. Furthermore, NV centers can also be used as quantum sensors to detect temperature and magnetic and electric fields. The controlled production and placement of NV centers in photonic structures is of high relevance to engineer devices.<br/>In this direction, this work presents results obtained from our efforts to use of fs-laser pulses to generate active and spatially localized NV centers in CVD diamond, as well as the fabrication of polymeric optical microcavities, via two-photon polymerization, incorporated with nanodiamonts containing NV centers. Upon excitation of diamond using 150-fs pulses from a Ti:sapphire laser at 775 nm, with a repetition rate of 1 kHz, we have determined that active defects, with the least damage to the surface, can be generated using pulse fluence in the range of 11 – 34 mJ/cm², as observed by the typical fluorescent emission of NV center. For fluences higher than 34 mJ/cm² the damage on the diamond’s surface started to get too severe, also resulting in lower emission. Our results also revealed that the density of NV centers grows with the number of fs-pulses. The generation process, however, is stochastic. Furthermore, fs-pulse at ~800 nm (86 MHz repetition rate) were use to fabricate, via the two-photon polymerization (2PP), cylindrical resonators incorporated with nanodiamonds presenting centers. Even though the cavity quality factor (Q) decreases with the amount of nanodiamonds, for a cavity with 0.01 wt% of nanodiamonds Q ~10³ is achieved. More interestingly, we were able to collect the NV-center emission from specific positions in such microvities, that display the typical features of the NV-centers. In summary, The results reported here demonstrate the use of fs-laser pulses to generate localized center in diamond by using 150-fs pulses (775 nm) with fluences higher than 11 mJ/cm². Also 2PP was suceffuly used to fabricate microresonatores containg nanodiamonds, with Q of about 10³. The authors acknowledge FAPESP (grants 2018/11283-7, 2020/08715-2, 2019/27471-0, 2015/17058-7, 2013/07276-1, and 2009/54035-4), Air Force Office of Scientific Research, CNPq, and CAPES for financial support.