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.

The supercritical CO2 (scCO2) is widely used as solvent and transport media in different technologies. The technological aspects of scCO2 fluid applications strongly depend on spatial–temporal fluctuations of its thermodynamic parameters. The region of these parameters’ maximal fluctuations on the p-T (pressure-temperature) diagram is called Widom delta. It has significant practical and fundamental interest. We offer an approach that combines optical measurements and molecular dynamics simulation in a wide range of pressures and temperatures. We studied the microstructure of supercritical CO2 fluid and its binary mixture with ethanol in a wide range of temperatures and pressures using molecular dynamics (MD) simulation. MD is used to retrieve a set of optical characteristics such as Raman spectra, refractive indexes and molecular refraction and was verified by appropriate experimental measurements. We demonstrated that in the Widom delta the monotonic dependence of the optical properties on the CO2 density is violated. It is caused by the rapid increase of density fluctuations and medium-sized (20–30 molecules) cluster formation. We identified the correlation between cluster parameters and optical properties of the media; in particular, it is established that the clusters in the Widom delta acts as a seed for clustering in molecular jets. MD demonstrates that the cluster formation is stronger in the supercritical CO2-ethanol mixture, where the extended binary clusters are formed; that is, the nonlinear refractive index significantly increased. The influence of the supercritical state in the cell on the formation of supersonic cluster jets is studied using the Mie scattering technique.