Radiation Pressure Cross Section Research Articles

An approach for a polychromatic generalized Lorenz–Mie theory

In this work a polychromatic version of the generalized Lorenz–Mie theory stricto sensu (GLMT) is derived. In this new formalism, arbitrary time-dependent fields are expanded into partial waves using Bromwich scalar potentials and, instead of the usual expansion coefficients – the beam shape coefficients (BSCs) – found in the monochromatic GLMT, now one finds field shape spectra (FSSs) which are intrinsically frequency-dependent. Expressions for the incident, scattered and internal fields are presented, and it is shown how physical quantities defined and expressed in the monochromatic GLMT in terms of the BSCs are modified and redefined in terms of the FSSs in polychromatic light scattering problems, like scattered intensities and phase angles, absorption, extinction and scattering cross-sections, and radiation pressure cross-sections.

On longitudinal radiation pressure cross-sections in the generalized Lorenz–Mie theory and their numerical relationship with the dipole theory of forces

A recent work devoted to the longitudinal optical forces exerted by circularly symmetric Bessel beams on point-like particles in the Rayleigh regime of the generalized Lorenz–Mie theory (GLMT) confirmed the existence of nonstandard forces (named axicon forces in the context of Bessel beams) that seemingly cannot be expressed in terms of scattering and gradient forces traditionally discussed in the framework of the dipole theory of forces. These results lead to this question: Do the Rayleigh limit of the GLMT and the dipole theory of forces actually agree, or are they in disagreement? If so, the Rayleigh limit of the generalized Lorenz–Mie theory would have to be preferred because it provides a highly accurate formulation. To find a definitive answer to the question, numerical comparisons done between optical forces exerted in both frameworks demonstrated an extremely accurate agreement up to 1000 decimal places. This leads to the conjecture that the Rayleigh limit of GLMT might indeed exactly identify with the usual dipole theory of forces.

On transverse radiation pressure cross-sections in the generalized Lorenz–Mie theory and their numerical relationship with the dipole theory of forces

The Rayleigh limit of the generalized Lorenz–Mie theory (GLMT) and its relationship with the dipole theory of forces is investigated for transverse radiation pressure cross-sections and optical forces exerted over very small particles. If, at one hand, the GLMT provides interesting insights in terms of a multipole expansion and becomes restricted to contributions from (n=1)-partial waves, on the other hand the dipole theory incorporates the total electromagnetic fields and their interaction with an electric dipole. Simulations reveal an extreme accuracy between both approaches up to 3000 decimal places, thus reinforcing the conjecture that the Rayleigh limit of the GLMT might exactly identify with the traditional dipole theory of forces, although mathematically such identification remains to be uncovered.

Optical Bessel tractor polarized beams on a charged sphere of arbitrary size

Optical tractor beams can reel in an object towards the source, and are becoming a topic of significant worldwide research. Previous works considered the axial and transverse radiation pressure cross-sections (RPCSs) of optical tractor Bessel polarized beams on a dielectric sphere. However, most particles are charged, and it is important to investigate the tractor beam effect on charged particles. The aim of this work is therefore directed toward this goal, where the axial and transverse RPCSs for a charged sphere illuminated by a vector Bessel beam are computed in the framework of generalized Lorenz-Mie theory (GLMT). Numerical computations of the RPCSs are performed, with emphasis on the emergence of a negative pulling force and its dependence on the half-cone angle α0, the order l, and the polarization. A higher-order (l ≠ 0) Bessel beam possesses a hollow core and is of vortex nature, while the fundamental mode (l=0) is of non-vortex type and has a bright maximum intensity at the center of the beam. In our calculation, both l=0 and l=1 are considered. The axial PRCSs versus ka and α0 are first calculated, and the negative axial forces can arise. Moreover, the axial and transverse RPCSs in the plane perpendicular to the beam axis are computed. However, numerical results show that the RPCSs are same to that for a neutral particle. To explain this, the ratios of axial RPCSs for charged and neutral spheres are investigated taking ka as a parameter. The results show that charges only affect the RPCSs for small particles. Finally, the RPCSs for a charged sphere of relatively small are considered. The charge can affect the magnitude of the RPCSs, however, it does not affect the direction of axial optical forces. These results are of great importance in the development of novel optical tweezers and tractor beams.

High Radiation Pressure on Interstellar Dust Computed by Light-scattering Simulation on Fluffy Agglomerates of Magnesium-silicate Grains with Metallic-iron Inclusions

Abstract Recent space missions have provided information on the physical and chemical properties of interstellar grains such as the ratio β of radiation pressure to gravity acting on the grains in addition to the composition, structure, and size distribution of the grains. Numerical simulation on the trajectories of interstellar grains captured by Stardust and returned to Earth constrained the β ratio for the Stardust samples of interstellar origin. However, recent accurate calculations of radiation pressure cross-sections for model dust grains have given conflicting stories in the β ratio of interstellar grains. The β ratio for model dust grains of so-called “astronomical silicate” in the femto-kilogram range lies below unity, in conflict with for the Stardust interstellar grains. Here, I tackle this conundrum by re-evaluating the β ratio of interstellar grains on the assumption that the grains are aggregated particles grown by coagulation and composed of amorphous MgSiO3 with the inclusion of metallic iron. My model is entirely consistent with the depletion and the correlation of major rock-forming elements in the Local Interstellar Cloud surrounding the Sun and the mineralogical identification of interstellar grains in the Stardust and Cassini missions. I find that my model dust particles fulfill the constraints on the β ratio derived from not only the Stardust mission but also the Ulysses and Cassini missions. My results suggest that iron is not incorporated into silicates but exists as metal, contrary to the majority of interstellar dust models available to date.

Radiation pressure cross section exerted on homogenous dielectric spherical particle by zeroth order Mathieu beams

In this paper, we present a full calculation of radiation pressure cross section and optical forces exerted by linearly polarized zeroth order Mathieu beams on homogenous dielectric spherical particle in the framework of generalized Lorenz–Mie theory (GLMT). In this theory, the scattered fields are dependent upon the Mie scattering coefficients and the beam shape coefficients. So a new optical property such as force and torque appears by changing the beam profile and the nature of particle. In this way, this work is devoted to the analysis of both transverse and longitudinal optical forces exerted on a simple dielectric spherical particle by zeroth order Mathieu beams and zeroth order Bessel (which is a particular case of the first beam). Thus, through numerical simulations, we show that zeroth order Mathieu beams can׳t trap this particle but Bessel beam presents some dimensional stable equilibrium points.

RADIATION PRESSURE ON FLUFFY SUBMICRON-SIZED GRAINS

ABSTRACT We investigate the claim that the ratio β of radiation pressure force to gravitational force on a dust grain in our solar system can substantially exceed unity for some grain sizes, provided that grain porosity is high enough. For model grains consisting of random aggregates of silicate spherules, we find that the maximum value of β is almost independent of grain porosity, but for small ( < 0.3 &mgr; m ?> ) grains, β actually decreases with increasing porosity. We also investigate the effect of metallic iron and amorphous carbon inclusions in the dust grains and find that while these inclusions do increase the radiation pressure cross-section, β remains below unity for grains with 3 pg of silicate material. These results affect the interpretation of the grain trajectories estimated from the Stardust mission, which were modeled assuming β values exceeding one. We find that radiation pressure effects are not large enough for particles Orion and Hylabrook captured by Stardust to be of interstellar origin given their reported impact velocities. We also consider the effects of solar radiation on transverse velocities and grain spin, and show that radiation pressure introduces both transverse velocities and equatorial spin velocities of several hundred meters per second for incoming interstellar grains at 2 au. These transverse velocities are not important for modeling trajectories, but such spin rates may result in centrifugal disruption of aggregates.

Optical forces experienced by arbitrary-sized spherical scatterers from superpositions of equal-frequency Bessel beams

Radiation pressure cross sections over arbitrary-sized spherical scatterers are evaluated considering, as wave fields, recently developed frozen waves, which are a suitable superposition of equal-frequency Bessel beams, of arbitrary order. The so-called beam-shape coefficients are computed within the framework of the generalized Lorenz–Mie theory and with the aid of integral localized approximation. It is numerically shown that, under the paraxial regime, frozen waves could be designed to efficiently trap biological cells, viruses, bacteria, and so on, along multiple radial planes and at specific axial locations. Our results reinforce frozen waves as potential laser beams in optical trapping and manipulation.

Dust mantle of comet 9P/Tempel 1: dynamical constraints on physical properties

The trajectories of dust particles ejected from a comet are affected by solar radiation pressure as a function of their ratios of radiation pressure cross section to mass. Therefore, a study on the orbital evolution of the particles caused by the radiation pressure reveals the physical properties of dust on the surface of the comet nucleus. In the course of NASA's Deep Impact mission, the ejecta plume evolved under the influence of the radiation pressure. From the evolution and shape of the plume, we have succeeded in obtaining $\beta \approx 0.4$, where $\beta$ is the ratio of the radiation pressure to the solar gravity. Taking into account $\beta \approx 0.4$ as well as the observational constraints of a high color temperature and a small silicate-feature strength, dust particles ejected from the surface of comet 9P/Tempel 1 are likely compact dust aggregates of sizes $\approx 20\,\mu$m (mass $\sim 10^{-8}$\,g). This is comparable to the major dust on the surface of comet 1P/Halley ($\sim 10\mu$m) inferred from in-situ measurements and theoretical considerations. Since such dust aggregates with $\beta \approx 0.4$ must have survived on the surface against jets due to ice sublimation, the temperature of ice in the nucleus must be kept below 145\,K, which is much lower than equilibrium temperature determined by solar irradiation and thermal emission. These facts indicate that 9P/Tempel 1 has a dust mantle composed of $20\,\mu$m-sized dust aggregates with low thermal conductivities $\sim 1 \, {\rm erg\, cm}^{-1} \, {\rm K}^{-1}\,{\rm s}^{-1}$.

Radiation pressure cross sections and optical forces over negative refractive index spherical particles by ordinary Bessel beams

When impinged by an arbitrary laser beam, lossless and homogeneous negative refractive index (NRI) spherical particles refract and reflect light in an unusual way, giving rise to different scattered and internal fields when compared to their equivalent positive refractive index particles. In the generalized Lorenz-Mie theory, the scattered fields are dependent upon the Mie scattering coefficients, whose values must reflect the metamaterial behavior of an NRI scatterer, thus leading to new optical properties such as force and torque. In this way, this work is devoted to the analysis of both radial and longitudinal optical forces exerted on lossless and simple NRI particles by zero-order Bessel beams, revealing how the force profiles are changed whenever the refractive index becomes negative.

Fundamentals of negative refractive index optical trapping: forces and radiation pressures exerted by focused Gaussian beams using the generalized Lorenz-Mie theory

Based on the generalized Lorenz-Mie theory (GLMT), this paper reveals, for the first time in the literature, the principal characteristics of the optical forces and radiation pressure cross-sections exerted on homogeneous, linear, isotropic and spherical hypothetical negative refractive index (NRI) particles under the influence of focused Gaussian beams in the Mie regime. Starting with ray optics considerations, the analysis is then extended through calculating the Mie coefficients and the beam-shape coefficients for incident focused Gaussian beams. Results reveal new and interesting trapping properties which are not observed for commonly positive refractive index particles and, in this way, new potential applications in biomedical optics can be devised.

Optical properties of interstellar grain aggregates

We computed, through the transition matrix method, the optical properties of cosmic dust grains modelled as aggregates (clusters) of spheres with a Gaussian-like size distribution function. The calculation is performed without resorting to any approximation and with a computational effort that is noticeably lighter than the one required by other methods. Our results show that particle clustering produces an enhancement in the extinction and radiation pressure cross-sections per unit mass. These results might help in the identification of sustainable structures for dust grains in the typical physical and chemical conditions of the diffuse interstellar medium.

Radiation pressure cross-sections of fluffy interstellar grains

We computed, through the transition matrix method, the radiation pressure cross-sections of cosmic dust grains modelled as aggregates (clusters) of spheres of appropriate geometry. The calculation is performed without resorting to any approximation and with a computational effort that is noticeably lighter than the one required by other methods. Our results show that radiation pressure cross-sections decrease with increasing particle fluffiness in the near-ultraviolet and visible range of the spectrum. This is due to the decrease of the corresponding strength of the multiple scattering processes that couple the aggregated spheres to each other. As a result, the inertial response to radiation forces of highly porous aggregates tends to become similar to that of the constituent particles.

Radiation pressure on bacterial clumps in the solar vicinity and their survival between interstellar transits

Radiation pressure cross-sections for clumps of hollow bacterial grains with thin coatings of graphite are calculated using rigorousGuttler formulae. The carbonized skins are expected to form through exposure to solar ultraviolet radiation, but a limiting thickness of about 0.03 μm is determined by opacity effects. The ratios of radiation pressure to gravity P/G are calculated for varying sizes of the clumps and for varying thickness of the graphite coatings. Bacterial clumps and individual desiccated bacteria without coatings of radii in the range 0.3–8 μm have P/G ratios less than unity, whereas particles with coatings of 0.02μmthickness have ratios in excess of unity. Such coatings also provide protection from damaging ultraviolet radiation. Putative cometary bacteria, such as have beenrecently collected in the stratosphere, are thus not gravitationally bound in the solar system provided they possess carbonised exterior coatings. They are rapidly expelled from the solar system reaching nearby protosolar nebulae in timescales of a few million years. Even with the most pessimistic assumptions galactic cosmic rays are unable to diminish viability to an extent that vitiates the continuity of panspermia.

Axial force acting on a dielectric sphere in a focused laser beam

We present the detailed behavior of the axial force acting on a dielectric sphere exerted by the optical pressure of a focused Gaussian laser beam. Comparison is made between the numerical results and those calculated from the radiation pressure cross section. There is also a discussion as to whether the expressions for the axial force given in this paper are consistent with the previously reported experimental results. Moreover, a simple experimental method to measure the axial force on a polystyrene sphere suspended in water is demonstrated, and fairly good agreement between theoretical and experimental results was obtained.

Radiation pressure cross section for fluffy aggregates

—We apply the discrete dipole approximation (DDA) to estimate the radiation pressure cross section for fluffy aggregates by computing the asymmetry parameter and the cross sections for extinction and scattering. The ballistic particle–cluster aggregate and the ballistic cluster–cluster aggregate consisting of either dielectric or absorbing material are considered to represent naturally existing aggregates. We show that the asymmetry parameter perpendicular to the direction of wave propagation is maximized where the wavelength is comparable to the aggregate size, which may be characterized by the area-equivalent radius or the radius of gyration rather than the volume-equivalent radius. The asymmetry parameter for the aggregate depends on the morphology of the particle, but not on the constituent material. Therefore, the dependence of the radiation pressure cross section on the material composition arises mainly from that of the extinction and scattering cross sections, in other words, the single-scattering albedo. We find that aggregates consisting of high-albedo material show a large deviation of radiation pressure from the direction of incident radiation. When the aggregates are illuminated by blackbody radiation, the deviation of the radiation pressure increases with increasing temperature of the blackbody. Since the parallel component of the radiation pressure cross section for the aggregates is smaller than that for the volume-equivalent spheres at the size parameter close to unity, the Planck-mean radiation pressure cross section for the aggregates having radius comparable to the effective wavelength of radiation shows a lower value, compared with the volume-equivalent sphere. Consequently, the slope of the radiation pressure force per mass of the particle as a function of particle mass shows a lower maximum for the aggregates than for compact spherical particles.

Polycyclic aromatic hydrocarbon optical properties and contribution to the acceleration of stellar outflows

view Abstract Citations (36) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Polycyclic Aromatic Hydrocarbon Optical Properties and Contribution to the Acceleration of Stellar Outflows Cherchneff, Isabelle ; Barker, John R. ; Tielens, Alexander G. G. M. Abstract The optical constants of four polycyclic aromatic hydrocarbon (PAH) molecules (benzene, pyrene, pentacene, and coronene) are determined from their measured laboratory absorption spectra. The Planck mean of the radiation pressure cross section is computed for each molecule and for amorphous carbon (AC) grains, and semiempirically estimated for large PAH molecules up to 400 carbon atoms. Assuming that PAHs are present in carbon-rich stellar outflows, the radiation pressure forces acting on them are calculated and compared with the radiation forces on AC particles. The results show that PAHs possess very different optical properties from AC grains. Small PAHs may experience an 'inverse greenhouse' effect in the inner part of the envelope, as they decouple from the gas close to the photosphere. The radiation pressure force on PAHs is always much less than the force at work on AC grains, and PAH molecules do not affect significantly the dynamics of the outflow. Publication: The Astrophysical Journal Pub Date: August 1991 DOI: 10.1086/170383 Bibcode: 1991ApJ...377..541C Keywords: Aromatic Compounds; Cyclic Hydrocarbons; Interstellar Gas; Molecular Gases; Optical Properties; Stellar Envelopes; Absorption Spectra; Line Spectra; Radiation Pressure; Spectrum Analysis; Astrophysics; INTERSTELLAR: MOLECULES; STARS: CIRCUMSTELLAR SHELLS full text sources ADS |

Planck mean radiation-pressure cross sections for nonspherical grains. I

Planck mean radiation-pressure cross sections for nonspherical grains. I

Systematic studies of light scattering 1: Particle shape

The light scattering properties of twenty-eight particles, spanning four sizes (near the resonance region) and seven related shapes (a 4:1 cylinder, 4:1 and 2:1 prolate spheroids, a sphere, 2:1 and 4:1 oblate spheroids, and a 4:1 disk), are presented for a common index of refraction, m = 1.61-i0.004, representing silicates. Microwave analog and theoretical methods were used to derive the scattered intensity and degree of polarization as a function of the scattering angle along with the extinction. All results refer to an ensemble or a cloud of identical particles because averages have been taken over random particle orientations. The degree of polarization, backscatter, and the radiation-pressure cross section are most sensitive to particle shape, implying that the use of Mie theory may be inappropriate for many applications.