Dangerous high-power laser radiation has been used in technology for many decades, capable of damaging CCD and CMOS matrices (used in video cameras and lidars), as well as causing irreparable damage to the organs of vision. Damage occurs at a high-energy fluence density above a certain threshold value. The main disadvantages of the passive protection devices used – light filters – are color distortion and a narrow wavelength range that requires an accurate value of the wavelength of laser radiation that falls on a photosensitive material or device. The operation of a nonlinear optical limiter of laser radiation power for passive protection is based on the use of a material with a strong nonlinear optical response. However, existing materials do not have the low energy dimming threshold required for practice and, moreover, have insufficiently effective optical attenuation. Further improvement of these characteristics is necessary, although the results already achieved at the moment may well be used in practice. A nonlinear absorption coefficient was used to evaluate the effect of optical limiting. As a result of the studies carried out in this work on the example of composites of single walled carbon nanotubes with a tetra(cyclotriphosphazene)-substituted phthalocyanine ligand, we found that depending on the hydrodynamic radius of fine particles, the efficiency of optical limiting can increase by an order of magnitude. At the same time, the efficiency of optical limiting of composites is more than 2 times higher compared to the original nanotubes.
To protect photosensitive detectors and micro-optoelectromechanical systems, protective equipment is needed against the ingress of powerful laser radiation. Conventional color filters pose a problem for such devices by cutting out the region of the spectrum in which the laser operates. To ensure the possible operation, passive limiters based on nonlinear optical effects can be used. They are capable of transmitting non-hazardous laser radiation with insignificant attenuation (transmission of the order of 70%), and when hit by powerful laser radiation they can quickly darken. The urgency of this problem only increases with the development and widespread use of laser systems. In particular, when using lidars, receiving photosensitive detectors are often damaged. The use of various conjugates with carbon nanotubes is promising for creating limiters. In this work, it is proposed to use conjugates of dimeric phthalocyanine complexes of Cu to create nonlinear optical materials. This material demonstrates the ability to attenuate laser radiation with a nanosecond duration of 16 ns, even in the case of single pulses, due to the synergistic effect of absorption and scattering of radiation. In addition, in the case of 140 fs femtosecond periodic radiation, with a pulse repetition rate of 80 MHz, this material demonstrates the attenuation of radiation when using a cut-off diaphragm due to the effect of self-phase modulation (SSPM). The characteristics of the SSPM pattern were studied, it was noted that the outer rings have the greatest width. In general, the width of the rings gradually increases with distance from the center of the beam. At the same time, the peak fluence (highest fluence value) of each ring is approximately the same, with the exception of the central part. In the central region, a strong effect is observed from heated flows tending upward and thus strongly violating symmetry.
The effect of ultrashort laser radiation parameters on the process of biomaterial formation based on dispersed media of bovine serum albumin and carbon nanotubes was studied. It is noted that, in contrast to the use of continuous laser radiation of comparable power, the composite nanomaterial is formed when lower temperatures are reached, which provides additional advantages and a smaller change in the protein structure. This effect can also be associated with a pulse repetition rate of 80 MHz, in the interval, which is about 12.5 ns, partial cooling of the material can occur, while this effect is sufficient for the formation of a biomaterial. The hardness of this material is comparable to that of native tissue. A strong twofold change in the elasticity of such a material in comparison with drying in air indicates the formation of an inner framework of carbon nanotubes. The possibility of this effect is also confirmed by spectral studies, according to which, at the used wavelength of 810 nm, the radiation is absorbed mainly by carbon nanotubes and only as a result of heat transfer is transmitted to bovine serum albumin and is spent on water evaporation. In vitro studies of cell growth in the presence of biomaterial were carried out by quantitative (MTT test) and qualitative (microscopy) methods. It was found that the number of cells grown on the composites exceeds the number of cells in the control after 72 hours of incubation. The cells on the composites formed a monolayer, their morphology does not differ from the morphology of the cells in the control. In vitro studies indicate a positive effect of the biomaterial on cell adhesion and proliferation and, consequently, on the possibility of their use for tissue regeneration.
In this study, J-type dimeric copper phthalocyanine in dimethylformamide (DMF) was investigated to show strong nonlinear absorption due to the reverse saturable absorption (RSA) under single nanosecond pulses (16 ns at a wavelength of 532 nm), which significantly exceeds the lifetimes of excited states. In the case of a femtosecond laser, the effect of spatial self-phase modulation was observed, with no contribution from nonlinear absorption being found. The only linear absorption was detected under pulses of 140 fs at a wavelength of 790 nm. The femtosecond pulse repetition rate was 80 MHz which corresponds to a delay between single pulses of about 12.5 ns. Both analytical wavelengths used were outside the intense absorption region (Q- and B- bands) of J-type dimeric copper phthalocyanine in the UV/Vis/NIR spectrum. In the case of femtosecond laser radiation, a sufficient population of excited states was not achieved due to the low peak fluence (~ 0.03 mJ/cm2). For the single nanosecond pulses, the threshold fluence density was ca. 30 mJ/cm2. In the switch circuit, such material should be placed horizontally to exclude asymmetric thermal convection resulting from the gravity effect.
KEYWORDS: Current controlled current source, Raman spectroscopy, Spectroscopy, Hydrogen, Absorption, Heart, Medical research, Biopolymers, Bridges, Single walled carbon nanotubes
The structural parameters and vibrational IR and Raman spectra of the molecular unit of the chitosan polymer, chitosan dimer, and chitosan dimer in complex with SWCN fragment were calculated. It is shown that the interaction of the chitosan dimer with SWCNTs leads to a change in the valence angle of the COS linking the elementary units of the chitosan biopolymer and the valence angle of the hydrogen bond bridge C ... .NO. In the IR spectra, an increase in the intensity of the absorption bands in the region of ~1000 cm-1 is observed, and in the Raman spectra – an increase in the intensity of the lines in the low-frequency region of ~400-600 cm-1.
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.
At present, laser sources are widely used in many fields. Not only in laboratories, but also in sphere of medicine, manufacturing and military. Lasers are potentially dangerous to the eyes or sensitive optical devices, therefore it is necessary to develop optical limiters. One of the significant properties of carbon nanotubes is their optical limitation of laser radiation. Many works of scientific groups are devoted to materials for limiters, which include carbon nanotubes. However, they still have an increased interest. A particular role is given to such mechanism of nonlinear attenuation as scattering and absorption. Moreover, it is important not only their combined effect to increase the effectiveness of the limiters as a whole, but also the contribution of each of them with their combined effect. It is equally important to accurately determinate the concentration in which there is a strong attenuation of high-intensity laser radiation and minimal attenuation at low intensity. The nonlinear and linear optical properties of water-dispersed media with different concentrations of single-walled carbon nanotubes (SWCNTs) were obtained by optical density spectra, experimental Zscan data with an open aperture and a fixed location of the limiter. Radiation in single mode with duration of 16 ns at wavelength of 1064 nm from Nd:YAG laser was used. The linear transmittance of the prepared water dispersions of the SWCNTs ranged from 60% to 70%. Limiter with such working substances had attenuation coefficient 10 and 14 for the concentration of nanotubes 3.125 mg/l and 6.25 mg/l, respectively.
The technology of modification of the CNT array on a silicon substrate using laser radiation of nanosecond duration has been developed. The energy regime of irradiation of the array is determined with the aim of aligning the nanotubes perpendicular to the substrate. Structuring of CNTs at a given area using impulse nanosecond radiation moving using a galvanometric scanner system is obtained. Patterning was carried out using pulsed laser radiation with a wavelength of 1064 nm, which was moved by means of galvanometric mirrors over the area of the CNT array. The spatial profile of the beam was Gaussian. The energy density of the pulse was in the range 0.4-2.2 J/cm2. In order to obtain a homogeneous region of the CNT array after irradiation, the following parameters were set: the pulse duration was 100 ns, the radiation frequency was 30 kHz, at which the overheating of CNTs was minimized. The diameter of the laser beam at the focus of the laser was 20 μm. The moving rate of the laser beam of 500 mm/s was chosen in such a way so that individual pulses formed a continuous line with a laser beam overlap to compensate the changing in laser spot power along the diameter. Thus, the processed square 5×5 mm was formed by parallel lines 5 mm long, consisting of individual pulses located at a distance of 17 μm from each other. It is shown that the following effects are possible: CNT ablation, the effect of CNT alignment (straightening), singling, and “splicing” of individual CNTs in a single structure, as well as changing the morphology of the array itself. Nanotubes are less defective after laser modification. This is proved by Raman spectroscopy. The effect of CNT array structuring can be used to create new sensitive elements of photodetectors, solar cells, chemical sensors, temperature and pressure sensors, probes in microscopy and emitters.
The technology of cell 3D scaffolds laser fabrication is developed. 3D scaffolds are designed to repair osteochondral defects, which are poorly restored during the organism’s life. The technology involves the use of an installation, the laser beam of which moves along a liquid nanomaterial and evaporates it layer by layer. Liquid nanomaterial consists of the water-protein (collagen, albumin) suspension with carbon nanoparticles (single-walled carbon nanotubes). During laser irradiation, the temperature in the region of nanotubes defects increases and nanotubes are combined into the scaffold. The main component of installation is a continuous laser operating at wavelengh of 810 nm. The laser beam moves along 3 coordinates, which makes it possible to obtain samples of the required geometric shape. The internal and surface structure of the samples at the micro- and nanoscale levels were studied using the X-ray microtomography and scanning electron microscopy. In vitro studies of cell growth during 48 and 72 hours demonstrated the ability of cell 3D scaffolds to support the proliferation of osteoblasts and chondroblasts. Using fluorescence and atomic force microscopy, it was found that the growth and development of cells on a sample with a larger concentration of nanotubes occurred faster compared to samples with a smaller concentration of nanotubes.
Laser radiation limiters can be made on the basis of working substances, which have strong nonlinear effects after reaching a certain critical value (threshold limiting). Thus, it becomes possible to obtain a high transmission for a safe beam and a sharply reduced transmission for a hazardous beam. To determine the nonlinear and linear optical properties of these materials there were carried out comprehensive spectroscopic studies, experiments by Z-scan methods with an open aperture and a fixed location of the limiter. Working substances was developed which is suspension of conjugates J-type phthalocyanine dimers Zn or Mg with single-walled carbon nanotubes (SWCNTs) in water. Created conjugates can be used not only for protecting eyes and light-sensitivity elements, but for forming three-dimensional tissueengineered structures. Using conjugates J-type phthalocyanine dimers Zn and Mg with SWCNTs will increase the optical absorption in the wavelength range of laser processing by reducing the thermal effect on other substances in the composition of this structure. The Nd:YAG laser was used as the laser radiation source for generating pulses of 16 ns duration at a wavelength of 532 nm with the linearly polarized laser beam in the horizontal plane and a shape of Gaussian type. The threshold of limiting, linear and nonlinear absorption coefficients were determined by output characteristic, that was obtained by fixed location of the limiter. Created working substances have values of the following order: linear absorption coefficient ~ 3 cm-1 for layer of 0.2 cm thickness, low limiting threshold ~ 1 MW·cm-2 and high value of the nonlinear absorption coefficient ~ 550 cm GW-1 . Knowing the nonlinear optical parameters, Z-scan data with an open aperture can be calculated for comparison with experimental data.
Creation of limiters for intensive laser radiation requires the development of effective methods for testing materials to determine the nonlinear optical parameters characterizing their properties. The limiting threshold, linear and nonlinear absorption coefficients can be determined not only from data of Z-scan with open aperture, but also with the help of a fixed location of the limiter. The use of this method makes it possible to determine the output characteristic of the studied material from which nonlinear optical parameters can be calculated. Characteristics of carbon nanotubes and graphene oxide in water were obtained with the fixed location of the limiter. The experiments were performed using an Nd:YAG laser that generates pulses of 16 ns duration at a wavelength of 532 nm with the linearly polarized laser beam in the horizontal plane and a shape closed to Gaussian type. Theoretical curves for method of fixed location of the sample according to threshold model was calculated and compared with the experimental data. Normalized weakening coefficients, limiting threshold, linear and nonlinear absorption coefficients were found for studied dispersions and calculation of Z-scan with open aperture was made. The value of normalized weakening coefficient was higher in dispersed medium of SWСNTs with water (Knorm≈20) in comparison with oxide graphene in water (Knorm≈14). The dependences of normalized weakening coefficient bias input energy were approximately linear in both cases.
The study of structural properties of nanocomposites, based on different types of single walled carbon nanotubes (SWCNTs) and proteins (albumin, collagen), was carried out. The binding of protein molecules to the carbon component was described by Raman spectroscopy. Complex analysis of the structure and microporosity of nanocomposites was performed by the X-ray microtomography. The nanoporosity study was carried out using the low-temperature nitrogen porosimetry method. Samples based on SWCNTs with smaller size had the most homogeneity. With an increase in the concentration from 0.01 to 0.1 %, the mean micropore size increased from 45 to 93 μm, porosity in general increased from 16 to 28 %. The percentage of open pores was the same for all samples and was 0.02. As it was shown by Raman spectroscopy the protein component in nanocomposites has undergone irreversible denaturation and can act as a biocompatible binder and serve as a source of amino acids for biological tissues. These nanocomposites are bioresorbable and can be used to repair cartilage and bone tissue. This is especially important in the treatment of diseases of hyaline cartilage and subchondral bone.
The results of experimental creation of nanocomposites using femtosecond laser are presented. We have theoretically proved the formation of a carbon nanotube frame in a protein matrix during laser structuring of single-walled carbon nanotubes. We have selected the technological parameters of synthesis of nanocomposites, which provide the proliferation of living cells.
Creation of effective means of protection from laser radiation of high power requires the development of optical materials (working substance), with their transparence being decreased sharply above a certain critical value of the laser intensity due to the appearance of non-linear optical properties (limiting threshold). Based on the threshold model, the working substance of the optical limiter was characterized. Experimental data of z-scan with open aperture are used to determine the nonlinear optical parameters of solutions of dimeric phthalocyanine complexes of Mg and Zn of J-type in tetrahydrofuran (THF) and thin films of their conjugates with single-walled carbon nanotubes (SWCNTs). The output characteristic (output (peak) fluence vs input (peak) fluence), that describes the basic properties of optical limiters, was obtained with the fixed location of the optical limiter. Dimeric phthalocyanine complexes were found to have low limiting threshold ~ 2 MW·cm-2 and high value of the nonlinear absorption coefficient ~ 330 and 370 cm GW-1, respectively. Conjugates of these dimeric phthalocyanines with SWCNTs have been produced for the improving of the limiting parameters and increasing of the optical nonlinearity. Size of J-type dimeric phthalocyanine complexes of Mg and Zn were determined by the scanning electron microscopy (SEM). The atomic force microscopy (AFM) allowed to determine the dimensions of nanotubes. The structure parameters, such as diameter and defects as well as the strength of aggregates were estimated with the Raman spectroscopy. For our experiments, the lens with a focal length of 20 cm was used. As the laser radiation source, the Nd:YAG laser was used to generate pulses of 16 ns duration at a wavelength of 532 nm with the linearly polarized laser beam in the horizontal plane and a shape closed to Gaussian type.
3-D bioconstructions were created using the evaporation method of the water-albumin solution with carbon nanotubes (CNTs) by the continuous and pulsed femtosecond laser radiation. It is determined that the volume structure of the samples created by the femtosecond radiation has more cavities than the one created by the continuous radiation. The average diameter for multi-walled carbon nanotubes (MWCNTs) samples was almost two times higher (35-40 nm) than for single-walled carbon nanotubes (SWCNTs) samples (20-30 nm). The most homogenous 3-D bioconstruction was formed from MWCNTs by the continuous laser radiation. The hardness of such samples totaled up to 370 MPa at the nanoscale. High strength properties and the resistance of the 3-D bioconstructions produced by the laser irradiation depend on the volume nanotubes scaffold forming inside them. The scaffold was formed by the electric field of the directed laser irradiation. The covalent bond energy between the nanotube carbon molecule and the oxygen of the bovine serum albumin aminoacid residue amounts 580 kJ/mol. The 3-D bioconstructions based on MWCNTs and SWCNTs becomes overgrown with the cells (fibroblasts) over the course of 72 hours. The samples based on the both types of CNTs are not toxic for the cells and don't change its normal composition and structure. Thus the 3-D bioconstructions that are nanostructured by the pulsed and continuous laser radiation can be applied as implant materials for the recovery of the connecting tissues of the living body.
Laser welding device for biological tissue has been developed. The main device parts are the radiation system and adaptive thermal stabilization system of welding area. Adaptive thermal stabilization system provided the relation between the laser radiation intensity and the weld temperature. Using atomic force microscopy the structure of composite which is formed by the radiation of laser solder based on aqua- albuminous dispersion of multi-walled carbon nanotubes was investigated. AFM topograms nanocomposite solder are mainly defined by the presence of pores in the samples. In generally, the surface structure of composite is influenced by the time, laser radiation power and MWCNT concentration. Average size of backbone nanoelements not exceeded 500 nm. Bulk density of nanoelements was in the range 106-108 sm-3. The data of welding temperature maintained during the laser welding process and the corresponding tensile strength values were obtained. Maximum tensile strength of the suture was reached in the range 50-55°C. This temperature and the pointwise laser welding technology (point area ~ 2.5mm) allows avoiding thermal necrosis of healthy section of biological tissue and provided reliable bonding construction of weld join. In despite of the fact that tensile strength values of the samples are in the range of 15% in comparison with unbroken strips of pigskin leather. This situation corresponds to the initial stage of the dissected tissue connection with a view to further increasing of the joint strength of tissues with the recovery of tissue structure; thereby achieved ratio is enough for a medical practice in certain cases.
Dispersive and composite nanomaterials based on multi-walled and single-walled carbon nanotubes and its conjugates with dye of zinc phthalocyanine were produced. The composition and the structure of dispersive and composite materials were investigated using analytical methods of spectroscopy and microscopy. Nonlinear characteristic of nanomaterials of limiters by direct nonlinear scanning and Z-scan method were investigated. Studies suggest the possibility of using such nanomaterials in laser intensity limiters. Proposed threshold model characterizing limiters of powerful laser radiation takes into account the threshold nature of nonlinear interaction of irradiation with the nonlinear material. Threshold effect of nonlinear interaction of laser irradiation with several nonlinear material based on multi-walled and single-walled carbon nanotubes was experimentally found. It was shown that threshold model fit better with experimental data of Z-scan.
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