Nanosecond lasers have recently been widely involved in human activity. However, high-intensity laser radiation can cause severe damage to organs of vision and expensive photonic devices. Radiation in the near UV range is especially dangerous for human eyes, since it is strongly absorbed by biological media and is also invisible, i.e., the reaction time of the eye to such radiation is much lower than that of visible light. Passive limiters have high transmission (>70%) at a low light intensity and begin to “darken” only when the threshold value of the laser radiation intensity is reached. In this work, we studied liquid nanodispersed nonlinear optical limiters based on hybrids of single-walled carbon nanotubes (SWCNTs) with metal-free tetra(hydroxy)phthalocyanine (OH)₄PcHH). The value of the hydrodynamic radius of separate particles after (OH)₄PcHH binding increased from 288 ± 55 nm to 350 ± 60 nm, which confirms the attachment of phthalocyanine complexes to nanotubes. The third harmonic of a Nd:YAG nanosecond laser (355 nm, 20 ns) was used to study the nonlinear optical response. Based on a Z-scan with open-aperture and input-output dependence curves, third-order nonlinear optical absorption coefficients of 149, 236, and 229 cm/GW were obtained for dispersions of composites of SWCNTs and (OH)₄PcHH in water, dimethylformamide (DMF), and dimethylsulfoxide (DMSO), respectively. Threshold values did not exceed 100 mJ/cm². The Z-scan showed a gradual decrease in the duration of the laser pulse by 53%; however, near the focus, there was a sharp increase in the duration of the transmitted pulse, reaching a value of 29 ns in z = 0. This phenomenon confirms the occurrence of reverse saturable absorption in the investigated media and can be used in photonic devices to control the temporal characteristics of the signal. Thus, the possibility of protection of sensitive photonic devices and human eyes from nanosecond laser pulses in the near UV range by nanodispersed liquid media based on composites of SWCNTs with (OH)₄PcHH has been discussed in this paper.

The effect of the vacancy edge defect (bonds breaking between carbon atoms) of a graphene sheet on the Raman spectrum was studied. The spectra were calculated using the density functional theory (DFT) using the Gaussian-09 program. Modeling of a graphene sheet fragment with a break of one bond between carbon atoms at the edge showed that changes in the Raman spectrum were common for the presence of nitrogen and oxygen atoms. In this case, the strongest D lines appear in functionalized graphene with oxygen atoms, and the D. lines - in nitrogen-doped graphene. This is confirmed by the experimental Raman spectra as well as calculated ones. The strongest 2D line is characteristic of the graphene model without impurities; the presence of other oxygen or nitrogen atoms leads to a decrease in its intensity. Modeling of a graphene sheet fragment with a break of one bond between carbon atoms at the edge showed that changes in the spectrum are common for both cases of graphene nitrogen-doping and functionalization with oxygen atoms. A comparison of the experimental data with the simulation results showed good agreement between the data. Moreover, the vibrations of hydrogen atoms linked by covalent bonds with neighboring carbon atoms moved towards each other in disturbed hexagonal structures located on the edge of the graphene sheet. Such a steric effect led to a decrease in the frequency of the stretching vibration q(CH), which appeared in the region of similar to 2700 cm(-1) and corresponded to the 2D vibration. The results of the vacancy edge defect modeling for the graphene sheet fragment being nitrogen-doped and functionalized by oxygen atoms were compared with experimental data.

<!-- *** Custom HTML *** --> We studied the formation of a composite from an aqueous dispersed medium with albumin and carbon nanotubes under the action of laser radiation in continuous wave (CW) mode and pulsed mode with a repetition rate of 10 Hz and pulse duration of 16 ns. During the experiments, the temperature was monitored at the site of exposure, as well as its distribution in the liquid. Pulsed solid-state Nd:YAG laser and CW diode laser with an irradiation power of ∼500 mW were used as radiation sources. However, a three-dimensional composite was formed only with constant exposure. The effect of pulsed laser radiation with an intensity corresponding to nonlinear interaction with water dispersion led only to its enlightenment. Thus, it is important not only the energy parameters of radiation but also the frequency of energy portions exposure for the fabrication of tissue-engineered structures (composites). As a result, it was found that the curing of the dispersion and the composite formation occurs under the action of continuous or pulsed (with a high pulse repetition rate) laser radiation at a temperature in the range from 45°C to 50°C; in case the pulse repetition rate is insufficient, composite formation is not observed even under the action of high intensity radiation and heating occurs only to a temperature of ∼40 ° C. This formation process can be generated both in the visible 532 nm and in the infrared 810-nm wavelength ranges. In this case, one of the main conditions is the absence of albumin or cells absorption at these wavelengths so that absorption occurs mainly with single-walled carbon nanotubes. Studies of the surface and internal structure of the composite made it possible to demonstrate the binding of nanotubes to each other. This happened under the influence of laser radiation. This led to high hardness values of the composites. The average value of hardness was 0.26 ± 0.02 GPa.