Heating of three-layer solid aerosol particles by laser radiation

The heating of lidar-irradiated multilayer particles is analyzed theoretically and numerically by solution of the heat conduction equation. The internal intensity and temperature distributions are presented for particles composed of air, quartz, and carbon. It is shown that the heating times of such particles substantially depend on particle radii, layer position, and shell thickness. In particular, the decrease in thickness of the surface carbon layer can result in a reduction of the heating time of multilayer particles.     

Heating and destruction of metallic particles exposed to intense laser radiation

The heating of a laser-irradiated solid aluminum particle to boiling or to temperatures that exceed boiling is analyzed theoretically and numerically by solution of the heat-transport equation. Two different criteria of particle destruction are considered. The temperature distributions inside the particles depending on the intensity values and particle sizes are presented. It is shown that at the start of heating the contribution of heat exchange plays the dominant role, but as the boiling point is approached the contribution of vaporization plays the main role.     

Acceleration of particles by laser radiation scattered by a system of conductive spheres

An exchange of energy between a charged particle and an EM wave scattered by a conductive sphere or a system of conductive spheres has been calculated. Fields of the near-wave zone are responsible for energy exchange. A proper distribution of the scatterers leads to a cumulative change of the particle energy. The deflection of particles and radiative losses due to the scattered wave have been evaluated. Although both processes seem unimportant for acceleration of heavy particles (protons), they do restrict the acceleration of electrons, particularly the radiative losses. The system is studied as a model of a laser diffraction grating accelerator.     

Heating of thin films by laser radiation with allowance for the temperature dependence of the reflection coefficient

We solve the thermophysical problem of the heating of thin metal films on semiconductor substrates by laser radiation for linear and stepwise changes of the absorptivity as a function of the surface temperature.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 4, pp. 642–647, October, 1984.     

Formation of Cd particles by UV laser irradiation

Formation of the metal particles of Cd has been studied by nanosecond laser flash photolysis using an ArF excimer laser with the oscillation wavelength of 193 nm. The sample was a 10% methanol solution of CdCl₂. The solvated electron, e_aq⁻, was generated by the excitation of charge transfer bands of Cl⁻ to solvent. The e_aq⁻ efficiently reduced Cd²⁺ to Cd⁺ during a laser pulse of 30 ns (FWHM). The Cd particles were produced by the reaction between Cd⁺ and Cd⁺. In the air saturated solution, the Cd⁺ was easily oxidized by dissolved oxygen. The concentration of the Cd particles formed in the degassed solution was approximately twice of that in the air saturated solution.     

Heating of a massive spherical particle by radiation and convection

An approximate analytical solution of the nonlinear problem of heating of a spherical body by radiation and convection is obtained.     

Heating of polymer particles in plasma-jet sputtering

The heating of polymer particles on interaction with a high-temperature plasma-jet flux is considered. The distribution of the particle temperature fields at various Biot numbers is established.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 61, No. 5, pp. 756–762, November, 1991.     

Thermoelastic destruction of transparent media by laser radiation

It is shown that thermoelastic stresses may be the mechanism for the laser destruction of homogeneous transparent media having high thermal and elastical strength, at least during the initial stage of this destruction. Threshold values of the radiation density required for thermoelastic destruction are calculated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 15, No. 6, pp. 1093–1099, December, 1968.     

Production of ultrafine particles by nanosecond laser sampling using orthogonal prepulse laser breakdown

The particle size distribution and composition of nanosecond laser-generated aerosols from brass samples in atmospheric argon has been measured by low-pressure impaction and subsequent quantitative analysis of the aerosols by total reflection X-ray fluorescence. Ablation was performed applying a Nd:YAG laser at 1.06 microm both without and with a prepulse plasma breakdown generated by a second Nd:YAG laser at 2-60 micros prior to the ablation pulse. The beam of the prepulse laser had orthogonal direction to the ablation laser beam, and the breakdown was produced 2.5 mm above the ablation spot. Ultrafine aerosol particles (<50 nm) were generated in the double-pulse experiment representing practically the total mass impacted, while in single-pulse ablation the proportion of large particles (>0.1 microm) was dominating. The predominance of ultrafine aerosols in the prepulse experiment indicates that particle formation from vapor-phase condensation is the major mechanism, while the appearance of large particles in single-pulse ablation points at fragmentary evaporation in the laser-produced plasma. It was also shown that the total mass impacted in double-pulse ablation increases almost linearly with the power of the prepulse laser. The better atomization and the larger sample mass ablated can be assumed to be the main reasons for the increase of the line intensities in double-pulse laser-induced breakdown spectrometry with orthogonal prepulses reported by several research groups.     

Light scattering of ultrafine silica particles by VUV synchrotron radiation

Vacuum ultraviolet (VUV) light scattering from ultrafine silica particles is studied with an aerosol instrument recently established at the Advanced Light Source (ALS) in Berkeley. Silica particles, size-selected by a differential mobility analyzer, are introduced into vacuum through a set of aerodynamic lenses to form a particle beam. The scattered photons from the crossing area of the VUV synchrotron beam and particle beam are detected with a rotatable VUV photon detector. The angular distributions of scattered photons (ADSP) originating from 70, 100, 200 nm diameter silica particles are measured with 145.9 and 118.1 nm synchrotron radiation. These angular distributions show strong forward scattering. The measured ADSPs are consistent with simulation of Mie scattering. The refractive indices of silica particles, 2.6 + 1.1i and 1.6 + 0.0001i for 118.1 and 145.9 nm, respectively, are obtained by fitting the measured ADSPs; the least average percentage deviations are 18% and 6%, respectively. The scattered fluxes at widely different wavelengths (visible versus VUV) also exhibit clear size sensitivity. Under comparable experimental conditions of photon fluxes and detection efficiencies, limits of particle size detection of 70 and 250 nm are obtained, respectively, when using 118.1 and 532 nm illumination. As anticipated, VUV scattering is a more sensitive probe for ultrafine particles, which will find application in detection of these ubiquitous species beyond the confines of a laboratory.     

Heating of condensed particles in a gas flow

A solution is obtained for the heating of condensed particles in a gas flow, from which one derives an expression for the temperature reduction and rate of cooling of the gas.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 23, No. 6, pp. 1050–1053, December, 1972.     

Synthesis of ultrafine glass particles by laser ablation of microspheres

We describe a new method for producing ultrafine glass particles that employs pulsed-laser ablation of microspheres. Experiments were conducted using pulsed laser wave-lengths from 248 to 1064 nm with ≈ 10 ns pulses and with initial microsphere diameters from 8 to 60 μm. The ejected nanoparticles were collected on silicon substrates for analysis by computer-aided image processing of SEM micrographs to determine the effect of experimental parameters on the particle size distribution. Results showed mean particle diameters were as small as 59 nm and generally inversely proportional to laser fluence. The particle size distributions were closely log-normal with small geometric standard deviations.     

Absorption of the laser radiation by the laser plasma with gas microjet targets

An upper limit of absorption of the laser radiation in the plasma produced in a gas jet Xe target with the average density of (3–6) × 10¹⁸ cm^–3 and the effective diameter of 0.7 mm is found. It is equal to ≈50% and remains constant under any variation in this range of densities. This result contradicts both theoretical assessments that have predicted virtually complete absorption and results of earlier experiments with the laser spark in an unlimited stationary Xe gas with the same density, where the upper limit of absorption was close to 100%. An analysis shows that nonlinearity of absorption and plasma nonequilibrium lead to the reduction of the absorption coefficient that, along with the limited size of plasma, can explain the experimental results.     

Photoresonant ionization of gaseous media by excimer laser radiation

An identification is made of twenty five elements whose resonance lines overlap the emission lines of high-power pulsed ultraviolet gas lasers or lie in the immediate vicinity of them, so that the mechanism laser ionization based on resonance saturation (LIBORS) can be used to ionize the vapor of these elements. Resonance transitions of atoms and ions excited by the same laser (by krypton fluoride and xenon fluoride lasers, respectively) are observed for tantalum and uranium. It ishas been suggested that these elements may be used as “catalysts” for “ catalytic” resonance ionization (CATRION) of dense multicomponent gas mixtures. Experiments have been carried out to study the krypton fluoride laser irradiation of expanding vapor clouds of different elemental composition, created by the evaporation of targets with a ruby laser. Photographs obtained with an image converter, measurements of the refractive index gradient from the deflection of the laser beam, as well as probe and spectroscopic measurements indicate that the clouds undergo photoresonant ionization if they contain tantalum vapor but that the laser radiation has no influence otherwise. Pis’ma Zh. Tekh. Fiz. 23, 24–32 (May 12, 1997)     

Photoelectron emission induced by radiation of a nitrogen laser

The photoionization of various technological materials under the action of a pulsed nitrogen laser has been studied. It is shown that the photoeffect is produced mostly via the mechanism of two-photon ionization. The maximum photoionization efficiency was observed for a magnesium cathode.     

Nonstationary heating of two-dimensional metal nanoparticles by laser radiation

A numerical solution of the problem of nonstationary heating of a two-dimensional nanoparticle by laser radiation in the approximation of a constant temperature over the nanoparticle volume is presented. The asymptotes to the heating temperature for long times and for maximum heating of a nanoparticle at long durations of laser radiation have been obtained. It is shown that the temperatures of heating of silver and gold nanoparticles subjected to laser radiation at a resonance wavelength of plasmons are appreciable and may reach the boiling temperature of water. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 5, pp. 936–943, September–October, 2008.