Visualization of plasma-induced processes by a projection system with a Cu-laser-based brightness amplifier

A novel method for visualization of the process of interaction of high-power energy fluxes with various surfaces is proposed. The possibility of the dynamic visualization of a surface covered with a ∼3-cm-thick plasma layer with a linear density of ∼10¹⁶ cm⁻² is demonstrated experimentally. A scheme of intracavity shadowgraphy of phase objects with the use of a laser projection microscope is developed. Shadow images illustrating the development of the plasma torch of an erosion capillary discharge in air are presented.     

Polycrystal diamond growth in a microwave plasma torch

Diamond films of different structures were deposited on quartz, WC-Co, and molybdenum substrates in a microwave plasma torch discharge in an argon-hydrogen-methane gas mixture in a sealed chamber at pressures close to atmospheric by using the chemical vapor deposition technique. Images of diamond polycrystal films and separate crystals, as well as results of Raman spectroscopy, are presented. The spectra of optical plasma radiation recorded during film deposition demonstrate the presence of intense H_α hydrogen and C₂ radical bands known as Swan bands.     

Emission characteristics and properties of a laser-plume germanium plasma

The initial stage of the evolution of a laser-plume germanium plasma under typical deposition conditions of thin germanium films doped with nanoparticles was studied by emission spectroscopy. The velocity of the laser plasma, the ion recombination time, and the electron temperature and density at distances of 1 and 7 mm from the target surface exposed to high-power IR radiation are determined. The measured electron temperature and density are compared with the calculated ones. The differences in the emission characteristics and velocities of laser plasmas obtained by irradiating germanium targets with UV and IR lasers under similar conditions are examined.     

Diel aspects of the thermal structure and energy budget of a small English lake

SUMMARY. The did response of the thermal structure of Esthwaite Water to prevailing meteorological conditions was analysed for seven selected days, covering different phases of stratification. Meteorological measurements were combined with published empirical relations to compute 24-h thermal energy budgets for 2 days. Amplitudes of diel changes were controlled by the seasonal phase of stratification and the magnitude of incident solar radiation. Heat storage usually followed a sinusoidal curve with a minimum during the night and early morning and a maximum during the late afternoon. Wind-induced turbulent mixing, and vertical circulation induced by nocturnal cooling of the surface water through evaporative and conductive processes, also modified depth-time trends in thermal structure.
The budget accounted for almost all the thermal energy exchanges of the lake. Possible sources of a slight imbalance are considered. Although there was a positive daily surplus of net radiation, it may not always imply heat gain by the lake as it may be counter-balanced by heat losses through fluxes of latent and sensible heat, Net back-radiation was a major component of daily heat loss. The combined latent and sensible heat fluxes also accounted fora high proportion of heat loss to the atmosphere. Net flow of sensible heat to the lake was small but not always inappreciable. Net daily heat storage represented 26% (9 May) and 13% (17 June) of solar radiation Input. Advected energy due to lake inflow and outflow was negligible. Qualitative comparisons are made with long-term (seasonal and annual) energy budgets and heat fluxes.     

Repetitive torch in a coaxial waveguide: Temperature of the neutral component

The temperature of the neutral component in a repetitive microwave torch excited in an argon jet injected into atmospheric air is measured using different optical methods. The microwave energy is efficiently converted into the thermal energy of the argon jet. The gas temperature is maximum at the nozzle, where it reaches 4.5–5.0 kK, and decreases to 2.5–3.0 kK along the jet. The torch plasma, which is not in thermal equilibrium, drastically influences the working gas and the surrounding air.     

Computer Simulation of the Three-Dimensional Regime of Proton Acceleration in the Interaction of Laser Radiation with a Thin Spherical Target

Results from particle-in-cell simulations of the three-dimensional regime of proton acceleration in the interaction of laser radiation with a thin spherical target are presented. It is shown that the density of accelerated protons can be several times higher than that in conventional accelerators. The focusing of fast protons created in the interaction of laser radiation with a spherical target is demonstrated. The focal spot of fast protons is localized near the center of the sphere. The conversion efficiency of laser energy into fast ion energy attains 5%. The acceleration mechanism is analyzed and the electron and proton energy spectra are obtained.     

Mean radiant temperature in idealised urban canyons—examples from Freiburg, Germany

Studies on the thermal comfort of humans in urban areas require meteorological data such as air temperature, air humidity, wind speed, and short- and long-wave fluxes. In such studies radiation fluxes can be expressed by the mean radiant temperature—a parameter with high variability in urban areas due to variability in global radiation. Wind speed in urban areas is influenced by urban obstacles and their orientation. Both mean radiant temperature and wind speed can be modified or changed by different height-to-width ratios or orientation of urban structures. Modifications to these parameters by typical urban structures (represented by the height-to-width ratio) can result in variation of mean radiant temperature over a range of more than 30°C, which can correspond to three levels of thermal stress. The results presented here provide a possible means of comparing different urban configurations in different climate regions.     

532 nm和808 nm激光及其线偏振激光辐照人正常膀胱与膀胱癌组织光学特性

采用双积分球系统和光辐射测量技术的基本原理 ,以及运用生物组织的光学模型 ,研究了 5 32nm和80 8nm激光及其线偏振激光辐照人正常膀胱和膀胱癌组织的光学特性 .结果表明 :膀胱癌组织对同一波长的激光或其线偏振激光的衰减明显较正常膀胱组织的要大 ,膀胱癌组织对 5 32nm和 80 8nm激光的衰减均较其线偏振激光的要略大一些 .膀胱癌组织对 5 32nm和 80 8nm激光及其线偏振激光的衰减明显较正常膀胱组织的要大 .正常膀胱或膀胱癌组织对同一波长的激光及其线偏振激光的折射率均没有明显的差异 ,膀胱癌组织对 5 32nm和80 8nm激光的折射率比正常膀胱的明显要大 .Kubelka Munk二流模型下 ,两种组织对同一波长的激光或其线偏振激光的光学特性均有显著性差异 (P <0 0 1) .同一组织对不同波长的激光及其线偏振激光的光学特性也有显著性差异 (P <0 0 1) ,正常膀胱组织对同一波长的激光及其线偏振激光的光学性有明显差异 ,而膀胱癌组织对同一波长的激光及其线偏振激光的光学特性则没有明显差异 .膀胱癌组织对 5 32nm和 80 8nm激光及其线偏振激光的前向散射通量i (x)、后向散射通量 j (x)、总散射通量I (x)的衰减均较正常膀胱组织的明显要大得多 ,且其i (x)均明显较j (x)要强     

Some Results of the Application of the Probe Method to Studying Laser Plasma at the Radiation Intensity on the Target of ~109 W/cm2

Plasma Physics Reports - Three groups of charged particles are recorded at the impact of the laser radiation pulse with a metal target in a rarefied gas medium. The optical range laser radiation...     

SOLWEIG 1.0 – Modelling spatial variations of 3D radiant fluxes and mean radiant temperature in complex urban settings

The mean radiant temperature, T_mrt, which sums up all shortwave and longwave radiation fluxes (both direct and reflected) to which the human body is exposed is one of the key meteorological parameters governing human energy balance and the thermal comfort of man. In this paper, a new radiation model (SOLWEIG 1.0), which simulates spatial variations of 3D radiation fluxes and T_mrt in complex urban settings, is presented. The T_mrt is derived by modelling shortwave and longwave radiation fluxes in six directions (upward, downward and from the four cardinal points) and angular factors. The model requires a limited number of inputs, such as direct, diffuse and global shortwave radiation, air temperature, relative humidity, urban geometry and geographical information (latitude, longitude and elevation). The model was evaluated using 7 days of integral radiation measurements at two sites with different building geometries – a large square and a small courtyard in Göteborg, Sweden (57°N) – across different seasons and in various weather conditions. The evaluation reveals good agreement between modelled and measured values of T_mrt, with an overall good correspondence of R ²?=?0.94, (p?相似文献   

Laser surgery: using the carbon dioxide laser.

In 1917 Einstein theorized tha through an atomic process a unique kind of electromagnetic radiation could be produced by stimulated emission. When such radiation is in the optical or infrared spectrum it is termed laser (light amplification by stimulated emission of radiation) light. A laser, a high-intensity light source, emits a nearly parallel electromagnetic beam of energy at a given wavelength that can be captured by a lens and concentrated in the focal spot. The wavelength determines how the laser will be used. The carbon dioxide laser is now successfully employed for some surgical procedures in gynecology, otorhinolaryngology, neurosurgery, and plastic and general surgery. The CO2 laser beam is directed through the viewing system of an operating microscope or through a hand-held laser component. Its basic action in tissue is thermal vaporization; it causes minimal damage to adjacent tissues. Surgeons require special training in the basic methods and techniques of laser surgery, as well as in the safety standards that must be observed.     

丹江口水库淅川库区大气氮湿沉降特征

大气氮沉降是除河流输入外水库水体重要的外源氮输入途径。以丹江口水库淅川库区为研究区,于2018年11月至2019年10月在库区周边设置了6个采样点,采集并分析了库区大气氮湿沉降样品,探讨氮湿沉降的时空分布特征以及对水库水体外源氮输入的贡献。研究结果表明,研究区大气氮湿沉降量为24.21 kg hm^-2 a^-1,其中氨氮占比（47.45％）为最大,有机氮占比（36.34％）次之,硝氮占比（16.21％）最小。硝氮湿沉降量在空间上表现出显著差异性。氨氮、有机氮湿沉降量的季节差异显著,氨氮是以夏季最高,秋季次之,冬季最低,而有机氮是以秋季最高,夏季次之,冬季最低。氨氮、硝氮、有机氮湿沉降量之间存在显著相关性,氨氮、有机氮湿沉降量与降水量之间存在显著相关性。总氮、氨氮湿沉降量分别为1321.98 t/a和627.34 t/a,分别占河流总氮、氨氮入库量的10.82％、34.85％。研究结果可为探索有针对性的库区水体氮污染控制途径提供重要理论基础。     

Thermal plasma irradiation under the action of the microwave-frequency-modulated laser beam

The results of the calculation of the thermal irradiation of the laser plasma formed by a powerful laser beam with the microwave-frequency-modulated intensity are presented. The analytical solution has been obtained for the case of the light detonation regime. It has been shown that the modulation of the gasdynamic parameters due to the absorption of the laser radiation leads to the modulation of the spectral and integral brightness observed from the thermal plasma irradiation.     

Theoretical analysis of thermal damage in biological tissues caused by laser irradiation

A bioheat transfer approach is proposed to study thermal damage in biological tissues caused by laser radiation. The laser light propagation in the tissue is first solved by using a robust seven-flux model in cylindrical coordinate system. The resulting spatial distribution of the absorbed laser energy is incorporated into the bioheat transfer equation for solving temperature response. Thermal damage to the tissue is assessed by the extent of denatured protein using a rate process equation. It is found that for the tissue studied, a significant protein denaturation process would take place when temperature exceeds about 53 degrees C. The effects of laser power, exposure time and beam size as well as the tissue absorption and scattering coefficients on the thermal damage process are examined and discussed. The laser conditions that cause irreversible damage to the tissue are also identified.     

Methods of spatiotemporal measurements of line X radiation generated in laser plasmas on the Iskra-5 facility

The methods are described that were devised for spatiotemporal measurements of line X radiation generated in Al and Fe plasmas inside a 2-mm-diameter hollow spherical target whose inner surface was coated with a thin layer of the material to be investigated and which was irradiated by the second harmonic of the laser radiation in the Iskra-5 laser facility. The results of measurements are presented.     

Radiation therapy at compact Compton sources

The principle of the compact Compton source is presented briefly. In collision with an ultrarelativistic electron bunch a laser pulse is back-scattered as hard X-rays. The radiation cone has an opening of a few mrad, and the energy bandwidth is a few percent. The electrons that have an energy of the order of a few tens of MeV either circulate in storage ring, or are injected to a linac at a frequency of 10–100 MHz. At the interaction point the electron bunch collides with the laser pulse that has been amplified in a Fabry-Perot resonator. There are several machines in design or construction phase, and projected fluxes are 10¹² to 10¹⁴ photons/s. The flux available at 80 keV from the ThomX machine is compared with that used in the Stereotactic Synchrotron Radiation Therapy clinical trials. It is concluded that ThomX has the potential of serving as the radiation source in future radiation therapy programs, and that ThomX can be integrated in hospital environment.     

The mechanism of two-photon photochemical laser-induced deposition of silicon thin films from silane

We have investigated the mechanism of silicon thin film deposition by ArF excimer laser irradiation of silane gas diluted with argon. The Si films were deposited by a focused laser beam irradiating in parallel to silicon and silicon dioxide substrates at a gas flow rate of 20 SCCM, total pressure of 60 Torr and repetition rate of 15 Hz. At laser energy fluences higher than 160 mJ/cm² the deposition rate was almost independent of the incident laser energy, while at a lower energy the deposition rate depended strongly on the laser energy. A 3/2 power law was found for absorption measurements carried out at the same pressure under flow conditions and for several repetition rates at average laser power above 300 mW, regardless of the laser repetition rate. This kind of behavior is typical of a multiphoton absorption process involving saturation effects caused by focusing of the laser beam. Below 300 mW the power dependence indicated a two-photon absorption process. From the observed photochemical yield we found the value 5.7×10^-44 cm⁴ s molec^-1 for the two-photon absorption cross section.A Gaussian-shaped transverse thickness distribution of the deposited layer was obtained with a maximum value corresponding to the center of the laser beam spatial profile. This distribution depended on the deposition parameters, and was attributed to the diffusion process of silane decomposition products in the gas phase in the substrate. Analysis of the adsorption features of the process showed that the major product adsorbed on the substrate surface is silicon.An Arrhenius plot of the deposition rate versus the substrate temperature exhibits two regimes, each associated with a different activation energy. Between 340°C and 460°C the activation energy is 0.25–0.3 e. V, while between 500°C and 560°C it is 1.1 e. V. The activation energy in the higher temperature regime is similar to that found for thermal nonlaser assisted chemical vapor deposition. However, in the lower temperature regime the deposition process is mainly laser induced, and the value of the activation energy is due to the process of adsorption of the gas species on the substrate.     

Thermal effect existing in the action of carbon dioxide laser on the bone tissue]

In the experiments in vitro we have studied the influence of carbon dioxide laser radiation on bone tissues of man. We have found out the range and thermal effect dependence on the density of laser energy, the character and thickness of radiated tissues. We have determined the dynamics of temperatures at any time. The received results give us the possibility to differentiate the optimum regimen of radiation.     

The thermodynamic response of soft biological tissues to pulsed ultraviolet laser irradiation.

The physical mechanisms that enable short pulses of high-intensity ultraviolet laser radiation to remove tissue, in a process known as laser ablation, remain obscure. The thermodynamic response of biological tissue to pulsed laser irradiation was investigated by measuring and subsequently analyzing the stress transients generated by pulsed argon fluorine (ArF, lambda = 193 nm) and krypton fluorine (KrF, lambda = 248 nm) excimer laser irradiation of porcine dermis using thin-film piezoelectric transducers. For radiant exposures that do not cause material removal, the stress transients are consistent with rapid thermal expansion of the tissue. At the threshold radiant exposure for ablation, the peak stress amplitude generated by 248 nm irradiation is more than an order of magnitude larger than that produced by 193 nm irradiation. For radiant exposures where material removal is achieved, the temporal structure of the stress transient indicates that the onset of material removal occurs during irradiation. In this regime, the variation of the peak compressive stress with radiant exposure is consistent with laser-induced rapid surface vaporization. For 193 nm irradiation, ionization of the ablated material occurs at even greater radiant exposures and is accompanied by a change in the variation of peak stress with radiant exposure consistent with a plasma-mediated ablation process. These results suggest that absorption of ultraviolet laser radiation by the extracellular matrix of tissue leads to decomposition of tissue on the time scale of the laser pulse. The difference in volumetric energy density at ablation threshold between the two wavelengths indicates that the larger stresses generated by 248 nm irradiation may facilitate the onset of material removal. However, once material removal is achieved, the stress measurements demonstrate that energy not directly responsible for target decomposition contributes to increasing the specific energy of the plume (and plasma, when present), which drives the gas dynamic expansion of ablated material. This provides direct evidence that ultraviolet laser ablation of soft biological tissues is a surface-mediated process and not explosive in nature.     

Generation of high-quality charged particle beams during the acceleration of ions by high-power laser radiation

Numerous applications of protons and ions accelerated by laser radiation require charged particle beams of high quality (i.e., such that the ratio of the energy width of the beam to its mean energy is small). In order to produce beams with controlled quality, it is proposed to use two-layer targets in which the first layer consists of heavy multicharged ions and the second layer (thin and narrow in the transverse direction) consists of protons. The possibility of generating a high-quality proton beam in the interaction of ultraintense laser radiation with such a two-layer target is demonstrated by two-and three-dimensional particle-in-cell computer simulations.