Nano-plasmonic antennas in the near infrared regime

Plasmonic nano-antennas constitute a central research topic in current science and engineering with an enormous variety of potential applications. Here we review the recent progress in the niche of plasmonic nano-antennas operating in the near infrared part of the spectrum which is important for a variety of applications. Tuning of the resonance into the near infrared regime is emphasized in the perspectives of fabrication, measurement, modeling, and analytical treatments, concentrating on the vast recent achievements in these areas.     

Nucleation of atmospheric aerosol particles

A significant fraction of the total number of particles present in the atmosphere is formed originally by nucleation from the gas phase. Binary nucleation of sulphuric acid and water, ternary nucleation of sulphuric acid, water and ammonia and ion-induced nucleation are thought to be the most important aerosol nucleation processes in the atmosphere. Within the last two decades, instrumentation to observe and characterize nucleation has improved greatly and numerous observations of nucleation have been made including quantification of the nucleation rate, characterization of the growth process and first chemical characterizations of the freshly formed particles. Nucleation has been observed at many different places in the atmosphere: in the boundary layer, in the free troposphere, in remote locations, in coastal areas, in boreal forests as well as urban areas and pollution plumes. In most cases gaseous sulphuric acid is assumed to be the key precursor gas. After nucleation, other supersaturated substances, especially low vapour pressure organics often take part in the subsequent aerosol growth. Iodine oxides seem to be responsible for nucleation observed in some coastal areas.Recent advances in modelling allow for a kinetic treatment of the nucleation process based on measured thermochemical data for the cluster formation. Considerable improvement over the classical nucleation treatment is expected from this approach.A detailed understanding of atmospheric aerosol nucleation processes is needed as the freshly formed particles directly influence the number concentration and size distribution of the atmospheric aerosol. The formation of clouds and precipitation is affected and influences on climate are anticipated. Anthropogenic emissions influence atmospheric aerosol nucleation processes considerably.Despite the comprehensive research efforts, substantial inconsistencies remain and conflicting results of laboratory studies, model studies as well as atmospheric observations persist. Several key questions about the predictability of atmospheric nucleation in general, about the substances, that take part in nucleation and subsequent growth and about the size and composition of the critical cluster, have not been resolved so far. To cite this article: J. Curtius, C. R. Physique 7 (2006).     

Charging of mm-size insulating particles in vibratory devices

The aim of this paper is to provide a better understanding of the factors that influence the efficiency of the vibratory devices employed for triboelectrostatic separation application. The experiments were carried out on mm-size disk-like polyamide particles introduced in polypropylene boxes that were subjected to rigorously controlled vibrations. The charge imparted by friction and impact was found to be significantly influenced by the characteristics of the vibratory movements, the residence time of the particles in the tribocharging device, and the number of particle–wall collisions.     

Dynamics of Abelian Higgs vortices in the near Bogomolny regime

The aim of this paper is to give an analytical discussion of the dynamics of the Abelian Higgs multi-vortices whose existence was proved by Taubes ([JT82]). For a particular value of a parameter of the theory, , called the Higgs self-coupling constant, there is no force between two vortices and there exist static configurations corresponding to vortices centred at any set of points in the plane. This is known as the Bogomolny regime. We will develop some formal asymptotic expansions to describe the dynamics of these multi-vortices for close, but not equal to, this critical value. We shall then prove the validity of these asymptotic expansions. These expansions allow us to give a finite dimensional Hamiltonian system which describes the vortex dynamics. The configuration space of this system is the moduli space—the space of solutions of the static equations modulo gauge equivalence. The kinetic energy term in the Hamiltonian is obtained from the natural metric on the moduli space given by theL ² inner product of the tangent vectors. The potential energy gives the intervortex potential which is non-zero when is not given by its critical value. Thus the reduced equations for the evolution of the vortex parameters take the form of geodesics, with force terms to express the departure from the Bogomolny regime. The geodesics are geodesics on the moduli space with respect to the metric defined by theL ² inner product of the tangent vectors, in accordance with Manton's suggestion ([Man82]). This allows an understanding of the two main phenomenological issues—first of all there is the right angle scattering phenomenon, according to which two vortices passing through one another scatter through ninety degrees. Secondly there is the conjecture from numerical calculations that vortices repel for greater than the critical value, and attract for less than this value. The results of this paper allow a rigorous understanding of the right angle scattering phenomenon ([Sam92, Hit88]) and reduce the question of attraction or repulsion in the near Bogomolny regime to an understanding of the potential energy term in the Hamiltonian ([JR79]).     

Light-induced drift of aerosol particles in gas mixtures

We analyze the motion of an aerosol particle in a gas mixture in which the molecules of one of the components have been selectively excited as to velocity by resonant optical radiation. We derive expressions for the force with which the gas acts on the particle and for the velocity of particle motion in the Knudsen regime. We also examine the dependence of the force and velocity of photophoresis on the offset of the radiation frequency from the center of the absorption line and on the concentration and mass ratios of the molecules of the absorbing and buffer gases. Zh. éksp. Teor. Fiz. 116, 1313–1328 (October 1999)     

Digital holographic imaging of aerosol particles in flight

This work describes the design and application of an apparatus to image aerosol particles using digital holography in a flow-through, contact-free manner. Particles in an aerosol stream are illuminated by a triggered, pulsed laser and the pattern produced by the interference of this light with that scattered by the particles is recorded by a digital camera. The recorded pattern constitutes a digital hologram from which an image of the particles is computationally reconstructed using a fast Fourier transform. This imaging is validated using a cluster of ragweed pollen particles. Examples involving mineral-dust aerosols demonstrate the technique's in situ imaging capability for complex-shaped particles over a size range of roughly 15-500 μm micrometers. The focusing-like character of the reconstruction process is demonstrated using a NaCl aerosol particle and is compared to a similar particle imaged with a conventional microscope.     

Observation of the critical regime near Anderson localization of light

The transition from diffusive transport to localization of waves should occur for any type of classical or quantum wave in any media as long as the wavelength becomes comparable to the transport mean free path l*. The signatures of localization and those of absorption, or bound states, can, however, be similar, such that an unequivocal proof of the existence of wave localization in disordered bulk materials is still lacking. Here we present time resolved measurements of light transport through strongly scattering samples with kl* values as low as 2.5. In transmission, we observe deviations from diffusion which cannot be explained by absorption, sample geometry, or reduction in transport velocity. Furthermore, the deviations from classical diffusion increase strongly with decreasing l* as expected for a phase transition. This constitutes an experimental realization of the critical regime in the approach to Anderson localization.     

Charging of heated colloidal particles using the electrolyte Seebeck effect

We propose a novel actuation mechanism for colloids, which is based on the Seebeck effect of the electrolyte solution: Laser heating of a nonionic particle accumulates in its vicinity a net charge Q, which is proportional to the excess temperature at the particle surface. The corresponding long-range thermoelectric field E is proportional to 1/r(2) provides a tool for controlled interactions with nearby beads or with additional molecular solutes. An external field E(ext) drags the thermocharged particle at a velocity that depends on its size and absorption properties; the latter point could be particularly relevant for separating carbon nanotubes according to their electronic band structure.     

Charging energy and stability of charged metallic particles

The stability of a charged metallic particle is investigated within the classical theory. The minimal number of atoms for which a charged spherical particle is stable against the spheroidal deformation, which relaxes the energy cost due to the Coulomb repulsion between extra charges, is derived. It is suggested that, for negatively charged particles, an extra electron virtually bound to particle is emitted before the fragmentation due to the Coulomb repulsion between extra charges will occur.     

Optical properties of single mixed-phase aerosol particles

We examine the light scattering from wet aerosol particles whose core morphology is a random Gaussian sphere coated by different amounts of water. We compare the results with those calculated from a concentric-sphere particle and from a homogeneous-sphere particle whose refractive index is determined from the Bruggeman mixing rule. In nearly all cases the differences between those of the Gaussian-core and the concentric-sphere particles are small. The most significant differences are seen in calculations of the asymmetry parameters and the intensity and polarization phase functions. The results of the homogeneous-sphere particles vary significantly from those of the Gaussian-core particles, typically an order of magnitude greater than for the concentric-sphere particles. It is not uncommon to see differences of 10% in the efficiencies of large, homogeneous-sphere particles; whereas, in the intensity and polarization phase functions, differences of several tens of percent are not uncommon.     

On the effect of trapped particles in the regime of cyclotron resonance

The motion of particles in a finite amplitude wave, propagating obliquely to the homogeneous magnetostatic field is discussed. As follows from simple integral properties, in the neighbourhood of Doppler-shifted cyclotron resonance similar trapping effects appear as in a plasma without magnetostatic field. Consequences of this trapping are discussed, in particular, the possibility of a strong absorption of the wave, and the origin of stochastic instabilities caused by the perturbation of an effective trapping potential and leading to the acceleration of particles.The author is indebted to Dr. R.Klíma, Dr. J.Lacina and Dr. P.unka for interesting discussions and to Dr. .Körbel, Mrs. P.Jaroová and Mrs. A.Harmáková for numerical calculations.     

Photophoresis of aerosol particles in a resonance radiation field

The additional force exerted by a gas on an aerosol particle on account of the change in recoil momentum of the gas molecules on the surface of the particle in a resonance radiation field is analyzed. Zh. Tekh. Fiz. 68, 88–89 (March 1998)     

保偏光纤中相近频率传输区域的调制不稳定性

利用激光脉冲在光纤中传播时所遵守的相干非线性薛定谔耦合方程,研究了保偏光纤中两相近频率的线偏振光，其偏振方向相互正交且平行于光纤的双折射轴，且偏振方向沿两个双折射轴的分量强度相等时，在同为反常色散区和正常色散区所产生的调制不稳定性.结果表明在反常色散区和正常色散区都能产生调制不稳定性；在正常色散区存在不同的调制不稳定性功率区域，对应不同的功率区域，导致增益谱表现出明显的不同，并且当输入功率一定时，波长差(或频率差)的变化导致增益谱的变化. 关键词： 相近频率传输区域 双折射 保偏光纤 调制不稳定性     

气溶胶单粒子粒径的实时测量方法研究

介绍了近期研制的一台实时测量大气气溶胶单粒子粒径和化学成分的仪器在如何测量气溶胶单粒子粒径方面的测量原理及特点，并结合激光解吸附电离飞行时间质谱技术，利用该仪器对木屑燃烧产生的烟气气溶胶粒子的实时测量结果. 关键词： 气溶胶粒子 空气动力学粒径测量方法 激光解吸附电离 飞行时间质谱