High-Temperature Transformation of Graphite Coating on Silica Surface under Continuous Laser Radiation

Size effect on surface structural relaxation kinetics of silica glass sample

Although luminescence of water during radiation irradiations with energy lower than the Cerenkov-light threshold were found recently, it was not still obvious whether the luminescence or scintillation is produced or imaging is possible in commonly used float or silica glass. Thus we tried to image the produced light from plates and a block made of float or silica glasses during irradiations of radiations. We clearly detected the images of the produced light of glass plates by using an electron multiplied (EM) CCD camera during irradiation of alpha particles for silica glass and float glass. The silica and float glass plates produced 13 photons/MeV and 258 photons/MeV for alpha particles, respectively. The light spectrum showed high intensity for longer wavelength in silica glass plate and it was relatively broad for float glass plate. By combining the float glass plate with a photomultiplier tube (PMT), energy spectrum could be measured for 5.5 MeV alpha particles with the energy resolution of 65% FWHM. We also measured the scintillation image during irradiation of proton to a float glass block. The image in float glass block during irradiation of proton showed light distribution similar to the dose in the glass. These results suggest float or silica glass plates or blocks are promising materials for radiation detection and imaging.

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.

Effects of secondary electrons emitted from surroundings on defect formation in silica glass under γ-ray irradiation

Background. Laser radiation is using in medicine for the diagnosis and treatment of many diseases. It is necessary therefore to know processes that occur at the same time. They are studiing for a long time, but not all know now. The problem of interaction of laser radiation with biological targets is important. Objective. The study of thermal processes in the skin and the lower layers when heated by laser radiation, which is introduced in the fiber tissue. Materials and methods. A mathematical model of the heating region inside the process biological tissue continuous and pulsed laser radiation. The radiation is introduced into the tissue by means of optical fiber. Used heat conduction equation in spherical coordinates with internal heat sources. Taken into account the removal of heat from the heated thermal conductivity region of tissue and blood flow. Results. Regimes of heating of biological tissue by continuous laser radiation, single radiation pulses and a series of radiation pulses. It is find the sizes of the heated region, the settling time and temperature gradients. Found the dimensions of the heat regions. They are determined by the fiber diameter, the depth of radiation penetration into the tissue and the speed of heat propagation in tissue. Thermal time constant of the process time is a few minutes. After heating of the pulse radiation at the same rate the fabric cools. Conclusion. To create a need to use laser light blue or green regions of the spectrum a small local area of heating. This radiation penetrates the biological tissue a few millimeters deep. To create large areas of heating should be used near infrared region of the spectrum, where the depth of light penetration into the tissue is equal to a few tens of millimeters. Heating pulse-modulated radiation different from the heating constant output only when the pulse repetition period longer than 1 minute. Then, during the time between pulses cloth cools. Average (smoothed), the heating temperature is the same as when heating a continuous radiation.

Exchange Bias Realignment Using a Laser-based Direct-write Technique

Increasing the heating efficiency and ignition rate of certain secondary explosives with absorbing particles under continuous infrared laser radiation

Growth of conical particles in carbon films deposited on silica glass fibers prepared by thermal chemical vapor deposition is investigated. The results show that the size and number of conical particles on the silica glass fiber increase with the film thickness and deposition temperature, but this effect is reduced when the carbon films are deposited on silica glass plates. The growth of conical particles on the silica glass fiber is mainly due to the small cross-sectional area of the fibers. These conical particles are against the hermetic property of carbon-coated optical fibers. We propose a method to minimize conical particles in carbon films on silica glass fibers.

The possibility of hair bonding by continuous laser radiation with a wavelength of 980 nm has been studied. A computer optical model of a laser system for bonding of human hair has been created. Using the Monte Carlo method, the distribution of the power of the absorbed laser radiation in the contact area of two hairs during their laser irradiation was obtained. The power distribution of the absorbed laser radiation obtained in the optical model is used in a computer thermophysical model of the laser bonding of human hair, the calculation in which is carried out by the finite element method. The maximum values of the temperature and the Arrhenius function of a pair of hairs in the area of their contact are calculated for different laser radiation power (1–10 W) and scanning speed of the laser beam along the area of hair contact (1–10 mm/s). It is shown that the temperature slowly decreases with increasing scanning speed, at the same time the Arrhenius function demonstrates a sharp decrease, while the values of both the temperature and the Arrhenius function increase with increasing laser radiation power. The power of laser radiation and the scanning speed at which the temperature of hair denaturation is reached, and the value of the Arrhenius function becomes equal to one were determined. Assuming that for the bonding of hair it is necessary that the temperature in the irradiation area exceeds the temperature of hair denaturation, and the Arrhenius function is less than one, the region of optimal laser radiation powers and scanning speeds is determined. In an in vitro experiment, the possibility of hair bonding by radiation from a continuous diode laser with a wavelength of 980 nm was studied and the validity of the optimal parameters of laser exposure selected at the stage of theoretical research was demonstrated. The results of the study can be used to develop a device for laser hair extension.

Features of heat/mass transfer and explosive water boiling at the laser fiber tip

Gain saturation characteristics of Raman amplification in silica and fluoride glass optical fibers

The heating characteristics of a lead selenide (PbSe) film under continuous laser radiation were investigated, accounting for the nucleation and increase in the thickness of an oxide phase layer. It is shown that oxidation of the PbSe film reduces the heating rate and lowers the maximum temperature due to a decrease in the fraction of absorbed laser radiation within the oxide phase. The modeling results presented in this work substantiate earlier experimental findings. For the first time, the explanation of the laser heating mechanism of the PbSe film enabled determining the most effective laser exposure duration to form structures with specified optical characteristics. The study was conducted using analytical modeling. A particular solution of the heat conduction equation was employed to describe the heat source. The optical properties of the film were characterized using Fresnel equations for light reflection and transmission. Based on previously obtained experimental data, an analytical model was developed to describe the heat source in the film, considering changes in its optical properties due to the formation of a lead selenide oxide layer and its increasing thickness. The findings show that, when the PbSe film is exposed to continuous laser radiation with a wavelength of 405 nm, the extinction coefficient of the film, kf, decreases from 0.488 to 1.62∙10–3 due to the formation of an oxide layer. In this case, the refractive index of the film, nf, similarly decreases from 3.532 to 1.925. The film absorption coefficient at the laser wavelength decreases from 0.68 to 0.03 during irradiation. As the thickness of the oxide phase increases from 0 to 600 nm, the temperature growth in the irradiated zone slows down, and the maximum temperature shifts from the surface toward the film-substrate interface. When exposed to continuous laser radiation with a power density of about 340 W/cm2 for 9 s, the maximum film temperature does not exceed 275 °C. The obtained results can be applied in the development of mid-infrared spectrum photo detectors based on PbSe film. Laser annealing of the film allows local and controlled changes in the optical and electrical properties of the PbSe film within a narrow range of values, thereby influencing the photo sensitivity of the film used as a detector for midand far-infrared radiation.

Photothermal therapy, in which a laser is an effective tool, is a promising method for cancer treatment. Laser parameters, including power, irradiation time, type of laser radiation (continuous or chopped), and the concentration of the photothermal agent, can affect the efficiency of this method. Therefore, this study investigated and compared the effects of different laser parameters on the efficiency of photothermal treatment for cervical cancer, which is the fourth most prevalent cancer in women. In addition, we investigated the properties of graphene oxide (GO) synthesized as a photothermal agent under laser radiation, and its effectiveness in achieving the desired therapeutic temperature. This study examined and compared the effects of temperature, nanoparticle concentration, irradiation time, and laser power to understand their impact on heat transfer. The toxicity of graphene oxide at different concentrations in HeLa cancer cells was also evaluated. These results demonstrated low toxicity, particularly after 24h, with approximately 10% toxicity. The study explored mortality under laser irradiation at various powers and time intervals using continuous and chopped beam irradiation. In addition, a model for temperature prediction using a regression tree was presented. Finally, the combined photothermal effects of graphene oxide and laser irradiation were investigated. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test results reveal significant effects, with a mortality rate of 90% in continuous radiation with a concentration of 0.3mg/ml and 75% in chopped beam irradiation with concentrations of 0.3 and 0.4mg/ml. A regression tree model was developed to predict temperature changes based on the GO concentration, laser power, and irradiation time, providing valuable insights for optimizing photothermal therapy parameters. Statistical analysis showed that the combined effect of graphene oxide with continuous laser irradiation was more effective than chopped-beam laser irradiation. However, the chopped-beam irradiation method is expected to cause less damage to surrounding tissues. These findings indicate that photothermal therapy with graphene oxide, chopped, and continuous laser irradiation can potently treat HeLa cancer cells and pave the way for further exploration of targeted cancer treatments.

Results of laboratory experiments on nonlinear propagation of high-power pulse-periodic and continuous CO2 laser radiation in a gas medium are presented. The experiments were carried out in a cell filled with a mixture of air and carbon dioxide in different partial concentrations (∼1–4%) under strong absorption and thermal blooming of laser radiation. The experimental conditions simulated the atmospheric propagation of high-power laser radiation along a kilometer-long path. Sharply focused laser beams were used; the regions of heat release along the beam channel were recorded by the shadow imaging technique. We found that, despite increased intensity, the focal waist of a laser beam is characterized by reduced heat release as compared to that in the pre- and postfocal beam regions. The saturation effect of the resonance absorption coefficient of CO2 at high pulse peak intensity (blooming effect) is considered as the most probable physical cause of the above feature. For continuous radiation, this effect is much weaker.

In this study, abrasive-free polishing of a single-crystal 4H-SiC (0001) substrate was investigated. Two different types of polishing plates, namely a synthetic SiO2 glass (quartz) plate and a soda-lime SiO2 glass plate, were used to polish the SiC substrate under atmospheric conditions at room temperature. The surface roughness after polishing was evaluated by differential interference contrast microscopy, phase-shift interferometric microscopy, and atomic force microscopy. In addition, the chemical bonding states of the SiC surface before and after polishing were analyzed by X-ray photoelectron spectroscopy. The experimental results showed that an oxide layer was formed on the SiC surface as a result of the chemical reaction between the interfaces of the synthetic SiO2 glass plate and the SiC substrate. This generated oxide layer was effectively removed by polishing with the soda-lime SiO2 glass plate, resulting in an atomically smooth SiC surface with a root mean square roughness of less than 0.1 nm for 1.5 h. Obtained experimental results indicate that the component materials, temperature and water adsorptive property of the soda-lime SiO2 glass play an important role in the removal of the tribochemically generated layer on the SiC surface during this polishing.