7656156
Optical guiding of absorbing nanoclusters in air.
We suggest a novel approach in all-optical trapping employing a photophoretic force for manipulation of absorbing particles in open air. We demonstrate experimentally the robust three-dimensional guiding, over the distances of a few millimeters, of agglomerates of carbon nanoparticles with the size spanned from 100 nm to 10 microm, as well as their acceleration up to velocities of 1 cm/sec. We achieve stable positioning and guiding of particles as well as simultaneous trapping of a large number of particles in a dual-beam optical trap created by two counter-propagating and co-rotating optical vortex beams.
18776849
Optical micromanipulation.
Optical micromanipulation has engendered some major studies across all of the natural sciences at the mesoscopic scale. Though over thirty-five years old, the field is finding new applications and has lost none of its dynamic or innovative character: a trapped object presents a system that enables a calibrated minuscule force (piconewtons or less) to be exerted at will, enabling precision displacements right down to the angstrom level to be observed. The study of the motion of single biological molecular motors has been revolutionised and new studies in the physical sciences have been realised. From the chemistry and microfluidic viewpoint, optical forces may remotely actuate micro-components and perform micro-reactions. Overall, optical traps are becoming a key part of a wider "optical toolkit". We present a tutorial review of this technique, its fundamental principles and a flavour of some of the recent advances made.
122043854
Acceleration and trapping of particles by radiation pressure
Micron-sized particles have been accelerated and trapped in stable optical potential wells using only the force of radiation pressure from a continuous laser. It is hypothesized that similar accelerations and trapping are possible with atoms and molecules using laser light tuned to specific optical transitions. The implications for isotope separation and other applications of physical interest are discussed.
14020328
Observation of a single-beam gradient force optical trap for dielectric particles.
Optical trapping of dielectric particles by a single-beam gradient force trap was demonstrated for the first reported time. This confirms the concept of negative light pressure due to the gradient force. Trapping was observed over the entire range of particle size from 10 μm to ~25 nm in water. Use of the new trap extends the size range of macroscopic particles accessible to optical trapping and manipulation well into the Rayleigh size regime. Application of this trapping principle to atom trapping is considered.
92866966
The Airborne Microparticle: Its Physics, Chemistry, Optics, and Transport Phenomena
Background.- Particle Levitation.- Elastic Light Scattering.- Basic Single Particle Measurements.- Continuum Transport Processes.- Non-Continuum Processes.- Thermodynamic and Transport Properties.- Inelastic Light Scattering.- Spectroscopies and Mass Spectrometry.- Particle Chemical Reactions.- Phoretic and Radiometric Phenomena.
98408906
Formation of cluster-assembled carbon nano-foam by high-repetition-rate laser ablation

Abstract.High-repetition-rate laser ablation and deposition of carbon vapours results in the formation of quite different carbonaceous structures depending on the pressure of the ambient Ar gas in the chamber. Diamond-like carbon films form at a pressure below ≈0.1 Torr whereas a diamond-like carbon nano-foam is created above 0.1 Torr. Although laser-deposited amorphous carbon films have been extensively investigated in the past, here we present what, to our knowledge, is the first report of the production of a granular low-density carbon nano-foam with rich fraction of sp3 bonding. The bulk density of various foam samples was in the range (2–10)×10-3 g/cm3, and the specific surface area was 300–400 m2/g. The resistivity of the foam measured at low-voltage (±30 V) is (1–3)×109 Ohm cm at room temperature and (1–10)×1013 Ohm cm at 80 K. The dc conductivity of this low-density carbon foam and its temperature dependence appears to be very close to that of RF-sputtered solid amorphous diamond-like carbon films.The presented kinetic analysis of the carbon vapour in the Ar ambient demonstrates qualitative agreement between the predicted laser plume parameters and those measured in the experiments. Theoretical predictions of the parameters and the process of carbon vapour diffusion through the ambient gas, allow us to propose a self-consisted periodic model leading to the formation of the carbon clusters in the experimental chamber.
122947659
Dislocations in wave trains
When an ultrasonic pulse, containing, say, ten quasi-sinusoidal oscillations, is reflected in air from a rough surface, it is observed experimentally that the scattered wave train contains dislocations, which are closely analogous to those found in imperfect crystals. We show theoretically that such dislocations are to be expected whenever limited trains of waves, ultimately derived from the same oscillator, travel in different directions and interfere - for example in a scattering problem. Dispersion is not involved. Equations are given showing the detailed structure of edge, screw and mixed edge-screw dislocations, and also of parallel sets of such dislocations. Edge dislocations can glide relative to the wave train at any velocity; they can also climb, and screw dislocations can glide. Wavefront dislocations may be curved, and they may intersect; they may collide and rebound; they may annihilate each other or be created as loops or pairs. With dislocations in wave trains, unlike crystal dislocations, there is no breakdown of linearity near the centre. Mathematically they are lines along which the phase is indeterminate; this implies that the wave amplitude is zero.
9881164
Development of an optical trap for microparticle clouds in dilute gases
Abstract.Long-duration experiments with clouds of microparticles are planned for the ICAPS facility on board the International Space Station ISS. The scientific objectives of such experiments are widespread and are ranging from the simulation of aerosol behaviour in Earth’s atmosphere to the formation of planets in the early solar system. It is, however, even under microgravity conditions, impossible to sustain a cloud of free-floating, microscopic particles for an extended period of time, due to thermal diffusion and due to unavoidable external accelerations. Therefore, a trap for dust clouds is required which prevents the diffusion of the particles, which provides a source of relative velocities between the dust grains and which can also concentrate the dust to higher number densities that are otherwise not achievable. We are planning to use the photophoretic effect for such a particle trap. First short-duration microgravity experiments on the photophoretic motion of microscopic particles show that such an optical particle-cloud trap is feasible. First tests of a two-dimensional trap were performed in the Bremen drop tower.
7231807
Principles for characterizing the potential human health effects from exposure to nanomaterials: elements of a screening strategy
AbstractThe rapid proliferation of many different engineered nanomaterials (defined as materials designed and produced to have structural features with at least one dimension of 100 nanometers or less) presents a dilemma to regulators regarding hazard identification. The International Life Sciences Institute Research Foundation/Risk Science Institute convened an expert working group to develop a screening strategy for the hazard identification of engineered nanomaterials. The working group report presents the elements of a screening strategy rather than a detailed testing protocol. Based on an evaluation of the limited data currently available, the report presents a broad data gathering strategy applicable to this early stage in the development of a risk assessment process for nanomaterials. Oral, dermal, inhalation, and injection routes of exposure are included recognizing that, depending on use patterns, exposure to nanomaterials may occur by any of these routes. The three key elements of the toxicity screening strategy are: Physicochemical Characteristics, In Vitro Assays (cellular and non-cellular), and In Vivo Assays.There is a strong likelihood that biological activity of nanoparticles will depend on physicochemical parameters not routinely considered in toxicity screening studies. Physicochemical properties that may be important in understanding the toxic effects of test materials include particle size and size distribution, agglomeration state, shape, crystal structure, chemical composition, surface area, surface chemistry, surface charge, and porosity.
In vitro techniques allow specific biological and mechanistic pathways to be isolated and tested under controlled conditions, in ways that are not feasible in in vivo tests. Tests are suggested for portal-of-entry toxicity for lungs, skin, and the mucosal membranes, and target organ toxicity for endothelium, blood, spleen, liver, nervous system, heart, and kidney. Non-cellular assessment of nanoparticle durability, protein interactions, complement activation, and pro-oxidant activity is also considered.Tier 1 in vivo assays are proposed for pulmonary, oral, skin and injection exposures, and Tier 2 evaluations for pulmonary exposures are also proposed. Tier 1 evaluations include markers of inflammation, oxidant stress, and cell proliferation in portal-of-entry and selected remote organs and tissues. Tier 2 evaluations for pulmonary exposures could include deposition, translocation, and toxicokinetics and biopersistence studies; effects of multiple exposures; potential effects on the reproductive system, placenta, and fetus; alternative animal models; and mechanistic studies.
4857532
Safe handling of nanotechnology
The pursuit of responsible nanotechnologies can be tackled through a series of grand challenges, argue Andrew D. Maynard and his co-authors.Take fiveThe spectre of possible harm — real or imagined — is threatening to slow the development of nanotechnology. In a Commentary this week a group of nanotechnologists outlines a series of five “grand challenges”. If they and their colleagues can rise to these challenges — which include development of new ways of measuring exposure to nanomaterials and assessing the health and environmental impact of that exposure — the true extent of any risks involved should become clear.
6900874
Toxic Potential of Materials at the Nanolevel
Nanomaterials are engineered structures with at least one dimension of 100 nanometers or less. These materials are increasingly being used for commercial purposes such as fillers, opacifiers, catalysts, semiconductors, cosmetics, microelectronics, and drug carriers. Materials in this size range may approach the length scale at which some specific physical or chemical interactions with their environment can occur. As a result, their properties differ substantially from those bulk materials of the same composition, allowing them to perform exceptional feats of conductivity, reactivity, and optical sensitivity. Possible undesirable results of these capabilities are harmful interactions with biological systems and the environment, with the potential to generate toxicity. The establishment of principles and test procedures to ensure safe manufacture and use of nanomaterials in the marketplace is urgently required and achievable.
6523559
The potential environmental impact of engineered nanomaterials
With the increased presence of nanomaterials in commercial products, a growing public debate is emerging on whether the environmental and social costs of nanotechnology outweigh its many benefits. To date, few studies have investigated the toxicological and environmental effects of direct and indirect exposure to nanomaterials and no clear guidelines exist to quantify these effects.
128196292
Photophoresis and the Descent of Particles into the Lower Stratosphere G. M. HDY National Centeror Atmospheric Research, Boulder, Colorado
Calculations are presented for the photophoretic force acting on an opaque spherical particle moving in the free molecule regime. The theoretical results are used to estimate the time of descent of small particles from high levels of an idealized stagnant atmosphere to the lower stratosphere. The theory indicates that a difference in settling times should exist between nonmetallic particles of low thermal conductivity and metal particles of higher conductivity. Despite such differences, the estimated descent times, for example, of 0.1-micron radius particles ranging from conductivities of 8 × 10−4 to 8 × 10−2 cal sec−1 cm−1 °K−1, traveling from 100 to 20 km altitude, remains approximately the same, the order of 1000 days. The photophoretic effect on particles of low conductivity can become appreciable below 30 km altitude. Nevertheless, this force does not appear to contribute significantly to decreasing the total time required for material to settle from very high altitude to the lower stratosphere.
31756878
Dust eruptions by photophoresis and solid state greenhouse effects.
We carried out experiments that show a gas pressure dependent ability of light to eject particles from a dust bed. Dust eruptions also occur upon removal of the light source. This can be attributed to a solid state greenhouse effect and photophoretic forces. This ejection mechanism works at light intensities larger than 6 kW/m2 but in extreme cases might work as low as 1 kW/m2. It can be applied to sunlit dust on Mars where it aids or triggers dust lift-off from the surface into the atmosphere. It is of importance for dusty bodies at the inner edge of protoplanetary disks where it leads to light induced erosion. The effect also offers a base for technical applications of dust removal in low pressure environments.
12929911
The photophoretic sweeping of dust in transient protoplanetary disks
Context: Protoplanetary disks start their lives with a dust free inner region where the temperatures are higher than the sublimation temperature of solids. As the star illuminates the innermost particles, which are immersed in gas at the sublimation edge, these particles are subject to a photophoretic force. 
 
Aims: We examine the motion of dust particles at the inner edge of protoplanetary disks due to photophoretic drag. 
 
Methods: We give a detailed treatment of the photophoretic force for particles in protoplanetary disks. The force is applied to particles at the inner edge of a protoplanetary disk and the dynamical behavior of the particles is analyzed. 
 
Results: We find that, in a laminar disk, photophoretic drag increases the size of the inner hole after accretion onto the central body has become subdued. This region within the hole becomes an optically transparent zone containing gas and large dusty particles (>>10 cm), but devoid of, or strongly depleted in, smaller dust aggregates. Photophoresis can clear the inner disk of dust out to 10 AU in less than 1 Myr. The details of this clearance depend on the size distribution of the dust. Any replenishment of the dust within the cleared region will be continuously and rapidly swept out to the edge. At late times, the edge reaches a stable equilibrium between inward drift and photophoretic outward drift, at a distance of some tens of AU. Eventually, the edge will move inwards again as the disk disperses, shifting the equilibrium position back from about 40 AU to below 30 AU in 1-2 Myr in the disk model. In a turbulent disk, diffusion can delay the clearing of a disk by photophoresis. Smaller and/or age-independent holes of radii of a few AU are also possible outcomes of turbulent diffusion counteracting photophoresis. 
 
Conclusions: This outward and then inward moving edge marks a region of high dust concentration. This density enhancement, and the efficient transport of particles from close to the star to large distances away, can explain features of comets such as high measured ratios of crystalline to amorphous silicates, and has a large number of other applications.
16360670
Optical trapping of absorbing particles
Radiation pressure forces in a focussed laser beam can be used to trap microscopic absorbing particles against a substrate. Calculations based on momentum transfer considerations show that stable trapping occurs before the beam waist, and that trapping is more effective with doughnut beams. Such doughnut beams can transfer angular momentum leading to rotation of the trapped particles. Energy is also transferred, which can result in heating of the particles to temperatures above the boiling point of the surrounding medium.
4388612
A revolution in optical manipulation
Optical tweezers use the forces exerted by a strongly focused beam of light to trap and move objects ranging in size from tens of nanometres to tens of micrometres. Since their introduction in 1986, the optical tweezer has become an important tool for research in the fields of biology, physical chemistry and soft condensed matter physics. Recent advances promise to take optical tweezers out of the laboratory and into the mainstream of manufacturing and diagnostics; they may even become consumer products. The next generation of single-beam optical traps offers revolutionary new opportunities for fundamental and applied research.
8197447
Biological applications of optical forces.
D ESIGN CON SID ERATION S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 Bll/ding a Trap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 Beam Steering 254 Trapping Lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 T RAPPIN G TH EORY . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .. . . . . . . . . . . . ... . . . . 260 Ray-Optics Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Electromagnetic Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 F ORCE M EASUREM EN T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Measurement of Trap Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 Physics of Trup Stiffness Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 B�ownia,! Motion During Force Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . 272 PlcotenslOmeters 273 Other Applications of Picotensiometry .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 Determinants of Trapping Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
19617452
Optical manipulation of airborne particles: techniques and applications.
In the following paper, we discuss new methods to trap and manipulate airborne liquid aerosol droplets. We discuss the single gradient force trapping of water aerosols in the 2-14 micron diameter range using both 532 nm and 1064 nm light, as well as the holographic optical trapping of arrays of aerosols. Using this holographic technique, we are able to show controlled aerosol coagulation. We also discuss two techniques based on the radiation pressure trapping of aerosols, namely the dual beam fibre trap and the controlled guiding of aerosols using Bessel beams. We conclude with a discussion of new topics for study based upon these techniques and some possible applications.
97089723
Radiometric levitation of micron sized spheres
Radiometric levitation of a 20‐μ‐diam dye‐impregnated glycerol sphere has been observed at intensities as low as ∼1 W/cm2 in air at 30 Torr. The levitation has been effected on both strongly absorbing spheres in the direction of the light and weakly absorbing spheres in the opposite sense. Both strongly and weakly absorbing spheres are found to laterally seek an intensity minimum. Consequently particles were stably held in the focused beam of an Ar+ laser (4880 A) operating in the TEM*01 (doughnut) mode.
121660308
Photophoresis of a spherical particle in a rarefied gas
On the basis of the linearized gas‐kinetic model equations solution (the BGK and the S model), a force affecting a unilaterally illuminated spherical particle in a rarefied gas is calculated. Numerical calculations of the photophoretic force and the particle motion velocity are carried out for the whole range of Knudsen numbers taking into account the particle’s thermophysical, optical, and accommodation properties. The results obtained are compared to the known theoretical and experimental data.
120398810
The photophoretic force
Abstract Photophoresis has many times been described qualitatively but quantitative information is scarce. Photophoretic-force measurements have been made with an apparatus that, in essence, compares the force with that of gravity. To the present, only light beams sufficiently intense to develop measurable forces with carbon black particles have been achieved. Unfortunately, these particles were actually agglomerates of smaller particles, making the former's properties such as density, considerably uncertain. Nevertheless, the results, in agreement with radiometer theory, show that the photophoretic force increases exponentially with particle radius. A gas pressure dependence, undetected by several previous investigators, was demonstrated also.
95095945
Table-top 50-W laser system for ultra-fast laser ablation
We have built a mode-locked Nd:YVO4 laser with a very long resonator which produces an average power of 50 W in 13-ps pulses at 1064 nm and was designed for applications in micro-machining, the deposition of optical thin films, and the growth of nano-clusters in the laser-ablated plumes. By operating the laser at very low mode-locking repetition rates (1.5 MHz, 2.6 MHz, and 4.1 MHz), high pulse power is available in a near diffraction limited beam, allowing focused intensities to exceed 1012 W/cm2 and permitting efficient evaporation of difficult materials such as Si. The high power also allows conversion into the second harmonic at 532 nm with an efficiency exceeding 80%. Measurements of the ablation mass in experiments with metals show a 30–100 times increase in the ablation rate compared to the conventional low-repetition-rate ns-range lasers.
53464777
Origin of magnetic moments in carbon nanofoam
A range of carbon nanofoam samples was prepared by using a high-repetition-rate laser ablation technique under various Ar pressures. Their magnetic properties were systematically investigated by dc magnetization measurements and continuous wave (cw) as well as pulsed EPR techniques. In all samples we found very large zero-field cooled-field-cooled thermal hysteresis in the susceptibility measurements extending up to room temperature. Zero-field cooled (ZFC) susceptibility measurements also display very complex behavior with a susceptibility maximum that strongly varies in temperature from sample to sample. Low-temperature magnetization curves indicate a saturation magnetization MS ≈0.35 emu g at 2 K and can be well fitted with a classical Langevin function. MS is more than an order of magnitude larger than any possible iron impurity, proving that the observed magnetic phenomena are an intrinsic effect of the carbon nanofoam. Magnetization measurements are consistent with a spin-glass type ground state. The cusps in the ZFC susceptibility curves imply spin freezing temperatures that range from 50 K to the extremely high value of >300 K. Further EPR measurements revealed three different centers that coexist in all samples, distinguished on the basis of g -factor and relaxation time. Their possible origin and the role in the magnetic phenomena are discussed.
100331053
Handbook of carbon, graphite, diamond, and fullerenes
The performance of a single-crystal diamond detector, grown by chemical vapour deposition, as an energy (2) Pierson H. O., Handbook of Carbon, Graphite. Diamonds and Fullerenes: Processing, Properties. Applications. Handbook of carbon, graphite, diamond and fullerenes 1993 Pierson.pdf 4.72 MB Handbook of preparative inorganic chemistry 1963 Vol 1,2 Brauer.pdf. but in other areas, less-ordered graphitic or amorphous carbon shells were also Pierson, H. O. in Handbook of Carbon, Graphite, Diamond and Fullerenes:. At high temperature, Mg can reduce not only carbon in the oxidation state of +4 in Pierson, H. O. Handbook of carbon, graphite, diamonds and fullerenes:. nanotoxicity of carbon nanotubes and graphene in biomedicine. Pierson, H.O. Handbook of Carbon, Graphite, Diamond, and Fullerenes: Properties. Section 4 of the article is devoted towards discussing the role of carbon and its (7) H O Pierson, Handbook of carbon, graphite, diamonds and fullerenes:. The main forms are diamond and graphite, and they exhibit markedly di erent Books Handbook of Carbon, Graphite, Diamond and Fullerenes Properties. Four different forms of carbon namely, Graphite, Activated H. O. Pierson, Handbook of Carbon, Graphite, Diamonds and Fullerenes: Processing, Properties. The growth of multi-walled carbon nanotube (MWCNT) and carbon nano (13) H. O. Pierson, Handbook of Carbon, Graphite, Diamond and Fullerenes:.
7412160
Experimental observation of an extremely dark material made by a low-density nanotube array.
An ideal black material absorbs light perfectly at all angles and over all wavelengths. Here, we show that low-density vertically aligned carbon nanotube arrays can be engineered to have an extremely low index of refraction, as predicted recently by theory [Garcia-Vidal, F. J.; Pitarke, J. M.; Pendry, J. B. Phys. Rev. Lett. 1997, 78, 4289-4292] and, combined with the nanoscale surface roughness of the arrays, can produce a near-perfect optical absorption material. An ultralow diffused reflectance of 1 x 10(-7) measured from such arrays is an order-of-magnitude lower compared to commercial low-reflectance standard carbon. The corresponding integrated total reflectance of 0.045% from the nanotube arrays is three times lower than the lowest-ever reported values of optical reflectance from any material, making it the darkest man-made material ever.