A strategy for nitrogen-vacancy (NV) center production in diamond under its irradiation by 266-nm femtosecond laser pulses is suggested: NV centers can be effectively and controllably created in the regime of nanoablation of a diamond surface. The NV concentration was found to increase logarithmically with the laser pulse number in the nanoablation regime, which is realized at a laser fluence of <0.6 J/cm2, whereas the NV formation rate was proportional to the sixth power of laser fluence. These dependencies could be explained by the photolytic mechanism of vacancy formation on the diamond surface and their subsequent laser-stimulated diffusion in the bulk. The femtosecond laser nanoablation of the diamond surface was demonstrated to be a promising tool to produce the requisite number of vacancies near the diamond surface and, hence, to manage the formation of NV complexes.

Stimulated by the recently observed strong delocalization of fs radiation in c:Si bulk, the numerical study of fs laser beam propagation and photoexcitation of silicon material has been performed. Two fundamental aspects-dissipation of laser energy due to two-photon absorption (TPA) and nonlinear beam transformation-have been elaborated to clarify the nature of this effect.It has been found that for incident pulse energy 100 µJ and tight beam focusing onto a spot of 6.5 µm diameter, due to TPA only a small part of the laser pulse energy (<1%) could reach the focal plane inside the Si bulk. As a result, the laser-produced e-h plasma density did not exceed ∼10 19 cm −3 and the bulk material damage (permanent modification) threshold was never reached. Additionally, the e-h plasma defocusing has been shown to give a contribution to the light delocalization, significantly widening the pulse propagation path. The data obtained are quite consistent with the experimental results.

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To transform a monocrystalline diamond into monocrystalline graphite, the exposure of an ultrafast laser to a (111) diamond face was investigated for the first time. The single pulse of the third harmonic of a Ti:sapphire laser (100 fs, 266 nm) was used to produce graphitized inclusions embedded in a (111) diamond substrate. Three different regimes of (111) diamond graphitization are discussed in this paper. Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to investigate the graphitized material, which was found to resemble highly oriented graphite at certain laser fluencies. The proposed approach to the problem of perfect local diamond graphitization is an important step toward creating all-carbon composite systems consisting of conductive and dielectric phases.

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