Photo-induced creation of nitrogen-related color centers in diamond nanocrystals under femtosecond illumination

Diamond nanocrystals deposited on a dielectric mirror at the focus of a microscope objective have been illuminated by femtosecond laser pulses. We have observed the photo-creation of color centers, under peak power corresponding to an intensity of about 50 GW/cm². In a nanocrystal initially containing a single Nitrogen Vacancy (NV) center, femtosecond illumination resulted in the transformation of this center into another one with different spectral features. These features are tentatively attributed to the neutral form NV⁰. This irreversible transformation goes together with the photocreation of other unstable color centers at the laser focus. Such behavior under femtosecond laser illumination place some limitations on the use of sub-picosecond pulses to trigger single photon emission from a single NV center in diamond nanocrystal.