Table Of ContentScatteringfrom ModelNonsphericalParticles
Physics of Earth and Space Environments
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F. Borghese P. Denti R. Saija
Scattering
from Model
Nonspherical
Particles
Theory and Applications
to Environmental Physics
SecondEdition
With 144 Figures
ABC
ProfessorDr.FerdinandoBorghese
ProfessorDr.PaoloDenti
Dr.RosalbaSaija
UniversitàdiMessina
DipartimentodiFisicadellaMateriaeTecnologie
FisicheAvanzate
SalitaSperone31
98166Messina
Italy
e-mail:[email protected]
[email protected]
[email protected]
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ISSN1610-1677
ISBN-10 3-540-37413-2SpringerBerlinHeidelbergNewYork
ISBN-13 978-3-540-37413-8SpringerBerlinHeidelbergNewYork
ISBN3-540-44014-3 1stEdition SpringerBerlinHeidelbergNewYork
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Nando
Preface to the Second Edition
Sincethepublicationofthefirsteditionofthisbook,wehavebecomedeeply
involved in astrophysics research, particularly the study of the interstellar
medium. Modeling scattering particles as layered spheres or as aggregates of
spherical scatterers, expanding the electromagnetic field in a series of vector
multipole fields, and resorting to the T-matrix approach for averaging over
the orientations of a dispersion of nonspherical particles are effective tools
forstudyingscatteringtheory,whichwedescribedandextensivelyappliedin
the first edition of this book. In fact, these tools also proved to be adequate
for studying cosmic dust, even when they must be applied to a new range
of current problems. We refer, for example, to the description of mechanical
interaction of electromagnetic radiation with cosmic dust grains, which is
believed to be of paramount importance in determining the dynamics of the
grains. Since this book is conceived as a summary of our work, the desire to
encompassallnewtopicsledustorevisebothitscontentanditsstructure.Of
course,beyondthechangesthatweoutlinebelow,allchapterswerecarefully
revised.
MarginalchangesandadditionsweremadeinChap.1,whileChap.2has
been substantially revised to cover the light of general polarization and, in
particular,withthedescriptionofthestateofpolarizationofelectromagnetic
waves of general form. In this chapter we reserved ample space for the rep-
resentation of the kinematics of the scattering processes both in the plane of
scattering and in the meridional planes. We also discuss a generalization of
the Stokes parameters that is suitable to describe the state of polarization of
waves of general form.
Chapter3presentsnovelmaterial,dealingwiththeconservationtheorems
for combined systems of fields and particles, and with their consequences.
Thus, this chapter deals not only with the widely known Poynting theorem,
but also with the conservation of linear momentum, which is responsible
for the radiation pressure and with the conservation of angular momentum,
which may be responsible for the (at least partial) alignment of the cosmic
dust grains, and the consequent linear polarization of starlight. The explicit
expressions for the radiation force F , the radiation torque Γ and the
rad rad
emission force F are presented.
e
VIII Preface to the Second Edition
Chapter 4 has been significantly revised. We introduce the appropriate
multipoleexpansionforwavesofgeneralwavevector(bothrealandcomplex)
and of general state of polarization. Formulas for the orientational averages
have also been reported for particles with cylindrical symmetry. Radiation
forces and torque dealt with in Chap. 3 are expressed here in terms of the
transition matrix.
Chapter 5, which deals with the calculation of the transition matrix of
aggregatesofsphericalscatterers,nowincludesthecaseofmetalspheresthat
can sustain the propagation of longitudinal waves.
Chapter6,dealingwithscatteringfromparticlesinthevicinityofaplane
interface, is almost unchanged. Nevertheless, we added new material relat-
ing to total internal reflection and scattering of evanescent waves, which is
presently considered a good method to study the properties of biological
particles, and is also relevant for near-field spectroscopy.
Chapter 7 has been greatly enlarged to include a number of new applica-
tions,suchasthescatteringbyaggregatesoflargespheres,andbyaggregates
of metal spheres sustaining longitudinal waves. We also include applications
regardingtheradiationforceandtorqueonaggregatesofsphericalscatterers
as well as regarding the force due to the emission of radiation.
TheonlyadditiontoChap.8relatestothescatteringofevanescentwaves
both from single spheres and from aggregated spheres.
No changes have been made in Chap. 9, while Chap. 10 now contains a
few new sections on the effect of radiation pressure and radiation torque on
cosmic dust grains. We also added a study of the morphology of the dust
grainsandofthedistributionandpolarizationoftheelectromagneticfieldin
the interior of aggregated dust grains. The subject of these new sections was
inspiredbythewideinterestoftheastrophysicistcommunityinthedynamics
of the interstellar medium and in astrochemistry.
We renew our thanks to Dr. Orazio I. Sindoni, Dr. Maria Antonia Iat`ı,
Prof. Santi Aiello and Dr. Cesare Cecchi-Pestellini, who we also mentioned
in the first edition and who were partners in the research we report in this
book. We also gratefully acknowledge the efforts of Dr. Arianna Giusto.
We want to express our sincere thanks to Prof. David Williams, Univer-
sity College London, whose understanding of all aspects of the astrophysi-
cal research has been the inspiration behind our astrophysics working, and
Prof. Flavio Scappini, Istituto per i Materiali Nanostrutturati del Consiglio
Nazionale delle Ricerche, Bologna, whose knowledge of astrochemistry was
invaluablewhenfacingcertainaspectsofthechemicaleffectsoftheradiation.
We are grateful to several colleagues for fruitful discussions that helped
us in revising the book. In particular, our sincere thanks go to Prof. Nikolai
Voshchinnikov, Sobolev Astronomical Institute, St. Petersburg, Russia, who
gave us good advice on the didactical aspects of the book.
Preface to the Second Edition IX
Last,butnotleast,wewanttothankSpringer,towhosepublishingpolicy
we owe the printing of this enlarged edition.
Messina, Italy Ferdinando Borghese
March 2006 Paolo Denti
Rosalba Saija
Preface to the First Edition
The Mie theory is known to be the first approach to the electromagnetic
scattering from homogeneous spheres endowed with all the accuracy of the
Maxwellelectromagnetictheory.Itappliestospheresofarbitraryradiusand
refractive index and marks, therefore, noticeable progress over the approx-
imate approach of Rayleigh, which applies to particles much smaller than
the wavelength. As a consequence, after the publication of the Mie theory in
1908,severalscatteringobjects,evenwhentheirshapewasknowntobenon-
spherical, were described in terms of equivalent spherical scatterers. It soon
became evident, however, that the morphological details of the actual parti-
cles were often too important to be neglected, especially in some wavelength
ranges. On the other hand, setting aside some particular cases in which the
predictions of the Mie theory were acceptable, no viable alternative for the
description of scattering from particles of arbitrary shape was at hand. This
situation lasted, with no substantial changes, until about 25 years ago, when
the exact solution to the problem of dependent scattering from aggregatesof
sphereswasdevised.ThissolutionisarealimprovementovertheMietheory
because several processes that occur, e.g., in the atmospheric aerosols and in
theinterstellarmedium,canbeinterpretedintermsofclusteringofotherwise
spherical scatterers. Moreover, nonspherical particles may be so distributed
(both in size and orientation) as to smooth out the individual scattering
properties.Inthiscase,aggregatesofsphericalscatterersmaybedesignedto
approximate the real objects through a wise choice of the geometry and of
the refractive indices of their components.
In the last 20 years, we have been active in the study of the scattering
properties of aggregates of spheres, to whose theory we and our cowork-
ers made some significant contributions that are, however, badly scattered
throughout the literature. For this reason, we resolved to collect in this book
these contributions organized within a coherent formalism, namely, the for-
malismofthemultipoleexpansionsintheframeworkofthetransitionmatrix
approach. The theory is supplemented by several results of calculations per-
formed by ourselves and by our coworkers, whose inclusion is meant to yield
information on the possible practical applications of the theory to systems
of interest. In order to achieve uniformity of representation, the calculations
were renewed and the results replotted. Therefore, this book should not be
