scholarly journals Interaction of a Low-Power Laser Radiation with Nanoparticles Formed over the Copper Melt in Rarefied Argon Atmosphere

Thermo ◽  
2020 ◽  
Vol 1 (1) ◽  
pp. 1-14
Author(s):  
Leonid A. Dombrovsky ◽  
Vladimir Ya. Mendeleyev
Keyword(s):  
Laser Radiation ◽  
Sample Surface ◽  
Copper Sample ◽  
Argon Atmosphere ◽  
Solid Sample ◽  
Surface Pattern ◽  
Probe Laser ◽  
Light Pressure ◽  
Scattering Effects ◽  
Copper Melt

Two effects have been recently observed by the authors for the copper sample melted in a rarefied argon atmosphere. The first of these effects is a strong decrease in the normal reflectance of a copper sample with time just after the beginning of melting. A partially regular crystal structure was also formed on the surface of the solid sample after the experiment. Both effects were explained by generation of a cloud of levitating nanoparticles. Additional experiments reported in the present paper show that the rate of decrease in reflectance increases with pressure of argon atmosphere and the surface pattern on the solid sample after the experiment depends on the probe laser radiation. It is theoretically shown for the first time that the dependent scattering effects in the cloud of copper nanoparticles are responsible for the abnormal decrease in normal reflectance and also for the observed significant role of light pressure in deposition of nanoparticles on the sample surface. The predicted minimum of normal reflectance is in good agreement with the experimental value.

scholarly journals An estimate of size of copper nanoparticles levitating over the melt surface using the measurements of spectral reflectance

2021 ◽  
Vol 2116 (1) ◽  
pp. 012060
Author(s):  
Leonid A Dombrovsky ◽  
Vladimir Ya Mendeleyev
Keyword(s):  
Laboratory Experiments ◽  
Copper Sample ◽  
Argon Atmosphere ◽  
Probe Laser ◽  
Spectral Measurements ◽  
Strong Decrease ◽  
Similar Time ◽  
Probe Laser Beam ◽  
Copper Melt ◽  
532 Nm

Abstract A strong decrease in normal reflectance of a probe laser beam of 660 nm wavelength reflected from the surface of copper sample just after the beginning of the sample melting in a rarefied argon atmosphere has been observed recently by the authors. A similar time dependence of the reflectance is obtained in the laboratory experiments of the present paper at the wavelengths of 532 nm. The additional spectral measurements enable the authors to estimate the size of condensed nanoparticles levitating over the copper melt.

Calculation of Spectral Optical Constants Using Combined Ellipsometric and Reflectance Methods for Smooth and Rough Bulk Samples

2021 ◽  
pp. 000370282110478
Author(s):  
Gilles Fortin
Keyword(s):  
Rough Surface ◽  
Optical Constants ◽  
Sample Surface ◽  
Infrared Region ◽  
Homogeneous Sample ◽  
Specular Reflectance ◽  
Scattering Effects ◽  
Spectral Ranges ◽  
Reflectance Measurements ◽  
Polarized Reflectance

Spectra of the optical constants n and k of a substance are often deduced from spectroscopic measurements, performed on a thick and homogeneous sample, and from a model used to simulate these measurements. Spectra obtained for n and k using the ellipsometric method generally produce polarized reflectance simulations in strong agreement with the experimental measurements, but they sometimes introduce significant discrepancies over limited spectral ranges, whereas spectra of n and k obtained with the single-angle reflectance method require a perfectly smooth sample surface to be viable. This paper presents an alternative method to calculate n and k. The method exploits both ellipsometric measurements and s-polarized specular reflectance measurements, and compensates for potential surface scattering effects with the introduction of a specularity factor. It is applicable to bulk samples having either a smooth or a rough surface. It provides spectral optical constants that are consistent with s-polarized reflectance measurements. Demonstrations are performed in the infrared region using a glass slide (smooth surface) and a pellet of compressed ammonium sulfate powder (rough surface).

Multiple beam scattering effects in biological tissues exposed to laser radiation

1988 ◽  
Vol 10 (2) ◽  
pp. 173-182
Author(s):  
F. Bloisi ◽  
L. Vicari ◽  
P. Cavaliere ◽  
S. De Nicola ◽  
P. Mormile ◽  
...  
Keyword(s):  
Laser Radiation ◽  
Biological Tissues ◽  
Multiple Beam ◽  
Scattering Effects ◽  
Beam Scattering

scholarly journals Инверсия вклада изотопа малой относительной концентрации в суммарный коэффициент поглощения смеси изотопов неона на переходе 3s-=SUB=-2-=/SUB=--2p-=SUB=-4-=/SUB=-

2019 ◽  
Vol 127 (8) ◽  
pp. 179
Author(s):  
Э.Г. Сапрыкин
Keyword(s):  
Numerical Modeling ◽  
Laser Radiation ◽  
Ground State ◽  
Optical Pumping ◽  
Discharge Plasma ◽  
Relative Concentration ◽  
Probe Laser ◽  
Decay Channels ◽  
Gas Discharge Plasma ◽  
Upper Level

AbstractAbsorption of probe laser radiation by a mixture of even isotopes of neon in a gas discharge plasma is investigated by the method of magnetic scanning of 3 s _2–2 p _4 transition. The contours of absorption lines of isotopes are resolved by means of numerical modeling. It is discovered that, upon decrease in relative concentration of one of the isotopes, its contribution to absorption is replaced by gain. The effect is found to be caused by radiative transfer of excitation energy between atoms of different kinds in the absence of a difference in level energies (the process known as optical pumping). The effect of this mechanism turned out to be substantial for the upper level transitions from which to the ground state are allowed while being absent for the lower level of the transition from which such transitions are forbidden although other decay channels are available.

scholarly journals Времяпролетные характеристики лазерного факела при абляции мишени MnSi в атмосфере аргона

2018 ◽  
Vol 44 (6) ◽  
pp. 103
Author(s):  
О.А. Новодворский ◽  
В.А. Михалевский ◽  
Д.С. Гусев ◽  
А.А. Лотин ◽  
Л.С. Паршина ◽  
...  
Keyword(s):  
Distribution Function ◽  
Laser Radiation ◽  
Langmuir Probe ◽  
Velocity Distribution Function ◽  
Argon Atmosphere ◽  
Gas Pressure ◽  
Buffer Gas ◽  
Laser Torch ◽  
Ion Velocity Distribution Function ◽  
532 Nm

AbstractThe Langmuir-probe technique has been used to study the time-of-flight characteristics of a laser torch during MnSi-target ablation in vacuum and argon atmosphere by pulsed 532-nm laser radiation at 15-ns pulse duration. It is established that the amplitude of the signal of fast particles in the laser torch nonmonotonically depends on the buffer-gas pressure. Mechanisms determining this dependence of laser-torch characteristics on the pressure are considered. The influence of buffer-gas pressure on the ion-velocity distribution function is determined.

scholarly journals SEPARATION OF PARTICLES IN POLYDISPERSE NANOSUSPENSION IN THE LASER RADIATION FIELD

2021 ◽  
pp. 146-155
Author(s):  
Валерий Иванович Иванов ◽  
Сергей Анатольевич Пячин
Keyword(s):  
Laser Radiation ◽  
Size Distribution ◽  
Radiation Field ◽  
Aqueous Suspension ◽  
Single Mode ◽  
Initial Distribution ◽  
Entire Volume ◽  
Light Pressure ◽  
Different Types ◽  
Laser Radiation Field

На основе стационарного решения уравнения диффузии изучена сепарация наночастиц в прозрачной полидисперсной водной суспензии с различными типами распределений по размерам под действием силы светового давления, возникающей в поле лазерного излучения интенсивностью 0,5 - 500 кВт/см. Установлено, что на дно кюветы преимущественно будут осаждаться частицы радиусом более 100 нм, а концентрация более мелких наночастиц во всем объеме суспензии останется без изменений. В случае симметричного начальное распределения наночастиц по размерам воздействие интенсивного светового пучка на суспензию приводит к нарушению симметрии кривой функции распределения, а также смещению максимума в область меньших размеров частиц на облучаемой поверхности. Если начальное распределение по размерам имеет несимметричный характер, исходное одномодовое распределение частиц по размерам трансформируется в двумодовое. Данная методика может быть использована для выделения наночастиц определенных размеров в зависимости от плотности мощности излучения. On the basis of a stationary solution of a diffusion equation separation of nanoparticles in a transparent polydisperse aqueous suspension with different types of size distributions was studied under the action of the light pressure arising in the laser radiation field with the intensity of 0,5 - 500 kW/cm. It was found that particles with a radius of more than 100 nm will mainly be precipitated at the bottom of the cell, and the concentration of smaller nanoparticles in the entire volume of the suspension will remain unchanged. In the case of a symmetrical initial distribution of nanoparticles size, the effect of a light beam with high intensity on the suspension leads to a violation of the symmetry of the distribution function curve, as well as a shift of the maximum to the region of smaller particle sizes on the irradiated surface. If the initial size distribution is asymmetric, the initial single-mode particle size distribution is transformed into a two-mode one. This technique can be used to isolate nanoparticles of certain sizes depending on the power density of the radiation.

Emission Spectrographic Analysis of Surfaces with an Ion-Sputtering Source

1976 ◽  
Vol 30 (5) ◽  
pp. 510-515 ◽  
Author(s):  
M. E. Waitlevertch ◽  
J. K. Hurwitz
Keyword(s):  
Power Supply ◽  
Sample Surface ◽  
Argon Atmosphere ◽  
Concentration Profiles ◽  
Spectrographic Analysis ◽  
Ion Sputtering ◽  
Square Wave ◽  
Source Current ◽  
Depth Concentration

An ion-sputtering source was installed and evaluated as an emission spectrographic source for the analysis of metal surfaces and for the determination of in-depth concentration profiles. This source generates a direct current glow discharge in a low-pressure argon atmosphere between a hollow stainless-steel anode and the sample (the cathode) and sputters material at a controlled rate from the sample surface. The resultant spectrum of the sputtered material is recorded photographically, and the analysis is completed by conventional spectrographic techniques. The power supply of the source can be operated in either a constant dc mode or a square-wave dc mode, but better repeatability and accuracy have been achieved with the square-wave dc mode. Before any significant sputtering occurs with this source, the voltage must exceed 240 Volts, the threshold sputtering voltage. The sputtering rate increases with both source current and voltage. This source has been used for the quantitative analysis of the surface of steel products and the determination of changes in composition with depth below the surface.

Atomic Emission Characteristics of Laser-Induced Plasmas in an Argon Atmosphere at Reduced Pressure

1989 ◽  
Vol 43 (2) ◽  
pp. 229-234 ◽  
Author(s):  
Yasuo Iida
Keyword(s):  
Thermal Characteristics ◽  
Sample Surface ◽  
Atomic Emission ◽  
Argon Atmosphere ◽  
Emission Characteristics ◽  
Reduced Pressure ◽  
Spatially Resolved ◽  
Emissive Region ◽  
Resultant Increase ◽  
Atomic Lines

The emission characteristics of laser-induced plasma, with the use of a Q-switched ruby laser of 1.5 J, were studied in argon atmosphere at reduced pressure. The time- and spatially resolved emission profiles were measured. In argon atmosphere at reduced pressure, the emission period of plasma is elongated to over a hundred microseconds, and the emissive region expands to more than a few tens of millimeters above the sample surface. The emission intensities of atomic lines increase severalfold in an argon atmosphere, in comparison with those obtained in air at the same pressure. Moderate confinement of plasmas and a resultant increase of emission intensities are achieved at 50 Torr. These results are explained by the chemical inertness and the thermal characteristics of the argon atmosphere and the decrease in absorption of the laser pulse by the plasma plume. The re-excitation of emissive species by collisions with metastable argon atoms seems to be less important.

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