共查询到20条相似文献,搜索用时 15 毫秒
1.
We present a compact fiber-based optical airborne particle trap that is integrated on a microscope slide. Light guided in a short glass capillary is used to inject micron-sized droplets into an optical trap formed by the same light and a counterpropagating beam emanating from a single-mode optical fiber. The glass capillary ensures separation of trapped particles from remaining aerosol in the injection chamber. Permanent alignment of the fibers and the capillary allows for adjustment-free operation. Mie resonances arising in the radiation pressure exerted on trapped droplets are detected via a position stabilization feedback loop and are used to precisely determine the size evolution of trapped glycerol–water droplets. 相似文献
2.
This paper reports on a test using laser Doppler anemometry of the hypothesis that the magnetomechanical effect involves rotation of the plasma of the positive gas-discharge column in an axial magnetic field. This was done by measuring the velocities of the dust macroparticles dropping in a vertical discharge tube. No rotation of the gas was revealed at a sensitivity of 40 cm/s. The rotation of dust particles suspended in striations and in the trap near the narrowed region of the discharge in a magnetic field was observed. The possible connection of this rotation with the magnetomechanical effect is discussed. 相似文献
3.
A. V. Zobnin A. P. Nefedov V. A. Sinel’shchikov V. E. Fortov 《Journal of Experimental and Theoretical Physics》2000,91(3):483-487
Self-consistent molecular-dynamics calculations of the charge of micron-size particles in a low-pressure gas-discharge plasma are performed. It is shown that charge exchange of ions on neutrals starts to affect the charge of dust particles at pressures corresponding to ion mean free paths much greater than the Debye radius. The computational results show that the potential of a particle depends nonmonotonically on the pressure and on the particle size. 相似文献
4.
G. E. Norman V. V. Stegailov A. V. Timofeev 《Journal of Experimental and Theoretical Physics》2011,113(5):887-900
The system of equations of motion of dust particles in a near-electrode layer of a gas discharge has been formulated taking
into account fluctuations of the charge of a dust particle and the features of the nearelectrode layer of the discharge. The
molecular dynamics simulation of the system of dust particles has been carried out. Performing a theoretical analysis of the
simulation results, a mechanism of increasing the average kinetic energy of dust particles in the gas discharge plasma has
been proposed. According to this mechanism, the heating of the vertical oscillations of dust particles is initiated by induced
oscillations generated by fluctuations of the charge of dust particles, and the energy transfer from vertical to horizontal
oscillations can be based on the parametric resonance phenomenon. The combination of the parametric and induced resonances
makes it possible to explain an anomalously high kinetic energy of dust particles. The estimate of the frequency, amplitude,
and kinetic energy of dust particles are close to the respective experimental values. 相似文献
5.
S. N. Antipov É. I. Asinovskiĭ A. V. Kirillin S. A. Maĭorov V. V. Markovets O. F. Petrov V. E. Fortov 《Journal of Experimental and Theoretical Physics》2008,106(4):830-837
A dusty plasma in a dc gas discharge is considered at low (cryogenic) temperatures of the gas. The formation of dusty plasma structures consisting of monodisperse poly(styrene) particles (d = 5.44 μm) in a dc glow discharge is experimentally investigated at cryogenic temperatures in the range from 4.2 to 77 K, and the results obtained are presented. The ion velocity distribution function and the charging of dust particles at cryogenic temperatures are calculated using the molecular dynamics method. The primary attention is focused on the correct inclusion of ion-atom collisions in the analysis. This is essential to the understanding of the main mechanisms of the experimentally observed increase in the density of dust particles with decreasing temperature of the gas in the discharge. 相似文献
6.
Development of a tunable mid-IR difference frequency laser source for highly sensitive airborne trace gas detection 总被引:4,自引:0,他引:4
Richter D Fried A Wert BP Walega JG Tittel FK 《Applied physics. B, Lasers and optics》2002,75(2-3):281-288
The development of a compact tunable mid-IR laser system at 3.5 μm for quantitative airborne spectroscopic trace gas absorption
measurements is reported. The mid-IR laser system is based on difference frequency generation (DFG) in periodically poled
LiNbO3 and utilizes optical fiber amplified near-IR diode and fiber lasers as pump sources operating at 1083 nm and 1562 nm, respectively.
This paper describes the optical sensor architecture, performance characteristics of individual pump lasers and DFG, as well
as its application to wavelength modulation spectroscopy employing an astigmatic Herriott multi-pass gas absorption cell.
This compact system permits detection of formaldehyde with a minimal detectable concentration (1σ replicate precision) of
74 parts-per-trillion by volume (pptv) for 1 min of averaging time and was achieved using calibrated gas standards, zero air
background and rapid dual-beam subtraction. This corresponds to a pathlength-normalized replicate fractional absorption sensitivity
of 2.5×10-10 cm-1.
Received: 29 April 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-303/497-1492, E-mail: dr@ucar.edu 相似文献
7.
The laser light scattering pattern in a wide angle is measured using a system designed and constructed to employ a linear 512-photodiode array for the morphological investigation of single microscopic particles and biological cells. The experimental intensity distribution exhibits a fairly good correlation with the size and structure of the microscopic object. The method is applicable to the real-time morphological analysis of individual biological cells in a flow system. 相似文献
8.
A He-Nc laser operating at 6328 Å produces beats between the modes for a linear cavity; these are related to the field distribution in the cross section of the beam. The power distribution in the modes is examined. 相似文献
9.
The polarizing effect of transverse dc magnetic fields applied to fractions of an isotropic single mode gas laser is theoretically investigated. A method is proposed to obtain prescribed orientations of the polarization plane in relatively weak external fields (He-Ne, 1.153 μ: about 3x10-3 Wb/m2). 相似文献
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A.V. Eremin E.V. Gurentsov M. Hofmann B.F. Kock C. Schulz 《Applied physics. B, Lasers and optics》2006,83(3):449-454
Time-resolved laser-induced incandescence (TR-LII) was applied for the determination of particle sizes during carbon-particle formation from supersaturated atomic carbon vapor that was generated by laser photolysis of carbon suboxide (C3O2) at room temperature. Thus, the solid carbon particles were formed under hydrogen-free conditions. The TR-LII technique was used for in situ size measurement of growing carbon particles and samples of final particles were analyzed by transmission electron microscopy (TEM). It was found that the particles grow to a final size of 4–12 nm within 0.02–1 ms. The properties of the obtained particles depend on the initial conditions in the reaction volume, i.e. concentration of carbon suboxide, pressure and type of gas diluter, photolysis wavelength, and laser pulse energy. The comparison of TR-LII and TEM particle sizing results yields information about the effective thermal energy accommodation coefficients for He, Ar, CO, and C3O2 molecules on carbon particles. PACS 61.46.Df; 07.60.-j; 78.70.-g 相似文献
12.
We describe a generator of narrow-band paired photons. A single retroreflected Ti:sapphire laser is used to cool, render transparent, and parametrically pump a cloud of (87)Rb atoms. We attain a paired-photon generation rate into opposing fibers of 600 counts/s with an intensity correlation function that has a width of 5 ns, and violates the Cauchy-Schwartz criteria by a factor of 2000. 相似文献
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The Mississippi State University Particle Sizing Instrument (MSU-PSI) is designed to perform real-time measurement of the particle-size distributions by means of non-intrusive methods. The instrument is based upon the principles of forward scatter of a laser beam by a single particle. Three beams are used to illuminate the particle. The green central beam is used to measure particles in the range of 2–15 μm in diameter. Two crossed blue beams are used to validate the trajectory of particles through the green beam. The size of a particle is determined by the amount of light that it scatters. This scattered light is captured and processed electronically and eventually is converted to a histogram, which, when interpreted, will be a representation of the particle-size distribution. In this paper, the model used to simulate the instrument numerically in the Ripple Validated Small Angle Near Forward Scattering (RVSANFS) mode is explained. 相似文献
16.
Spectroscopic measurements of excited particles in a N2 gas RF plasma-assisted carbon laser ablation
M.A. Bratescu N. Sakura D. Yamaoka Y. Sakai H. Sugawara Y. Suda 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1083-1088
In this work, we investigated a carbon plasma plume produced by laser ablation of a graphite target in a nitrogen gas environment. The spatial distributions of C and N atoms were measured by time-resolved absorption spectroscopy. The spatial distributions of the relative densities of CN radicals, C2, and C3 molecules were measured using time-resolved emission spectroscopy. We determined that nitrogen gas produced an increase in carbon atom and molecule densities in the ablation plume. It was observed that the addition of RF plasma to the plume increased the CN radicals and C atom densities, and decreased the C2 and C3 molecule densities. The RF plasma changed the evolution of various fractional species of C, N, CN, C2, and C3 in the ablation plume. The chemical reactions with and without RF plasma were explained using the evolution and density of the fractional species of C, N, CN, C2, and C3in the plume. PACS 52.38.Mf; 42.62.Fi; 33.20.-t; 81.05.Uw 相似文献
17.
A. V. Filippov M. N. Vasil’ev A. V. Gavrikov A. F. Pal’ O. F. Petrov A. N. Starostin V. E. Fortov 《JETP Letters》2007,86(1):14-19
Charging of dust particles in a plasma with the two-temperature energy distribution of electrons has been studied. It has been shown that the dust-particle potential divided by the electron temperature decreases with increasing electron temperature in the plasma with cold ions. Owing to this behavior, the potential of the dustparticle surface increases with the electron temperature more slowly than the linear function and is lower than the electron temperature (divided by the elementary charge) for T e > 5.5 eV in hydrogen and for T e > 240 eV in argon. The fraction of fast electrons at which these electrons begin to contribute to the charge of dust particles has been determined. It has been shown that the charge of micron particles can reach 106 elementary charges. The effect of the cold and thermal field emission on the charge of dust particles has been analyzed. The possibility of obtaining ultrahigh charges (to 107 elementary charges on dust particles with a radius of 50–100 μm irradiated by a 25-keV 1-mA electron beam has been demonstrated. 相似文献
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A Hamiltonian theory of motion for particles with internal structure, based on a dynamical bracket algebra, serves to define a generalized phase space for axially symmetric particles. Hydrodynamics of a gas of particles are explored through Liouville's and Boltzmann's equations and the equilibrium distribution function is obtained. Some modification of the pressure and density are necessary because of the spin and for a cold Fermi gas in thermal equilibrium they are shown explicitly.This work is based on a Ph.D. thesis of Y. Feldman submitted to Tel Aviv University in 1979. 相似文献