Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers

The scattering of the plane electromagnetic wave on the fiber-lake target is considered. The formula for the scattering cross section is used for building the kinetic equation that describes the propagation of the wave in the beam of parallel fibers. The evolution of intensity of the radiation propa...

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Опубліковано в: :Вопросы атомной науки и техники
Дата:2014
Автори: Shul'ga, N. F., Syshchenko, V. V.
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Мова:Англійська
Опубліковано: Національний науковий центр «Харківський фізико-технічний інститут» НАН України 2014
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Цитувати:Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers/ N. F. Shul'ga, V. V. Syshchenko// Вопросы атомной науки и техники. — 2014. — № 5. — С. 115-119. — Бібліогр.: 7 назв. — анг.

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Digital Library of Periodicals of National Academy of Sciences of Ukraine
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author Shul'ga, N. F.
Syshchenko, V. V.
author_facet Shul'ga, N. F.
Syshchenko, V. V.
citation_txt Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers/ N. F. Shul'ga, V. V. Syshchenko// Вопросы атомной науки и техники. — 2014. — № 5. — С. 115-119. — Бібліогр.: 7 назв. — анг.
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container_title Вопросы атомной науки и техники
description The scattering of the plane electromagnetic wave on the fiber-lake target is considered. The formula for the scattering cross section is used for building the kinetic equation that describes the propagation of the wave in the beam of parallel fibers. The evolution of intensity of the radiation propagating in the beam of straight and bent fibers is considered. Рассмотрено рассеяние плоской электромагнитной волны на нитевидной мишени. Полученное выражение для сечения рассеяния использовано при построении кинетического уравнения, описывающего распространение волны в пучке параллельных нитей. Рассмотрена эволюция интенсивности излучения, распространяющегося в пучке прямых и изогнутых нитей. Розглянуто розсiяння плоскої електромагнитної хвилi на нитевидної мiшенi. Отриманий вираз для перерiзу розсiяння використано для побудови кiнетичного рiвняння, що описує розповсюдження хвилi у пучку паралельних ниток. Розглянуто еволюцiю iнтенсивностi випромiнювання, що розповсюджується у пучку прямих та вигнутих ниток.
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fulltext ELECTROMAGNETIC WAVE SCATTERING ON A DIELECTRIC FIBER AND A SYSTEM OF PARALLEL FIBERS N.F.Shul’ga1, V.V.Syshchenko2∗ 1A. I.Akhiezer Institute of Theoretical Physics, National Science Center ”Kharkov Institute of Physics and Technology”, 61108, Kharkov, Ukraine; 2Belgorod State University, 308015, Belgorod, Russian Federation (Received April 8, 2014) The scattering of the plane electromagnetic wave on the fiber-lake target is considered. The formula for the scattering cross section is used for building the kinetic equation that describes the propagation of the wave in the beam of parallel fibers. The evolution of intensity of the radiation propagating in the beam of straight and bent fibers is considered. PACS: 41.20.Jb, 42.25.Bs, 42.25.Fx, 42.81.-i 1. INTRODUCTION The interaction of electromagnetic (EM) waves with fiber-like structures is widely used for control of prop- agation of optical radiation using (see, e.g., recent re- view [1] and references therein). The present paper considers the interaction of radiation of arbitrary fre- quency with fiber-like target. The kinetic equation describing propagation of the radiation in the system of parallel fibers (rope) is constructed. It is demon- strated that not only optical but also hard (up to X-ray domain) radiation could propagate along the rope following its bending under some conditions. 2. CROSS SECTION FOR WAVE SCATTERING ON A FIBER Scattering of EM wave by charged particle arises from oscillation of that particles under the action of the electric field of the incident wave (for incident wave of low intensity the influence of magnetic field would be negligibly small) that in its turn leads to emis- sion of secondary EM waves. This emission is inter- preted as the scattering of the incident wave; for the single charged particle the scattering cross section is described by well-known Thomson formula [2]. Let us consider the incidence of the plane monochromatic wave on the string of charges under the angle ψ to the axis of the string (Fig. 1). The electric field in the incident wave is described by the formula E(in)(r, t) = Ae(in) exp[i(k(in)r− ωt)], (1) where A is the wave amplitude, e(in) is the polariza- tion vector, k(in) is the wave vector, ω = |k(in)|/c is the frequency. Scattering of the wave on the string of charges could be described as the coherent sum of Thomson scatterings on the charges of the string. Fig.1. Incidence of the EM wave on the string of charges in the z direction causes their oscillations in the transverse plane The electric field of the wave scattered by n-th charge of the string could be presented on large dis- tance from it, R0 ≫ |rn|, as [3] En = e2A mω2R0 e−iω(t−R0/c) [[ e(in),k(out) ] ,k(out) ] × exp [ i(k(in) − k(out))rn ] , (2) where e and m are charge and mass of the oscillating particle (electron), k(in) is the wave vector of the scat- tered wave, rn is the radius vector of the n-th charge. After summation of the contributions of large num- ber of oscillating electrons forming the string, N ≫ 1, and calculation the intensity of the scattered radia- tion in ratio to the incident energy flux density we obtain the cross section of the wave scattering by the ∗Corresponding author E-mail address: syshch@bsu.edu.ru ISSN 1562-6016. PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY, 2014, N5 (93). Series: Nuclear Physics Investigations (63), p.115-119. 115 string of charges: dσ dΩ = 2π ( e2 m )2 N a [ k(out), e(in) ]2 ω2c2 × ∞∑ j=−∞ δ ( k (in) ∥ − k (out) ∥ − 2π a j ) , (3) where a is the period of the string, k (in) ∥ and k (out) ∥ are the components of the wave vectors of the inci- dent and scattered waves k(in) and k(out) parallel to the string axis. In the limiting case of small a, a < π/k(in) = λ/2, where λ is the wavelength (that means the transition from the discrete string of charges to the uniform fiber) the only nonzero term in the sum over j in (3) will be the j = 0 term. The cross section averaged over polarizations will be equal to dσ dΩ = πr20Ln 2 e 1 + ( ck (out) z ω )2  δ ( k (in) ∥ − k (out) ∥ ) , (4) where ne = 1/a is the number of electrons per unit length of the fiber, r0 = e2/mc2 is the electron clas- sical radius, L = Na is the total length of the fiber. Delta-function in (4) reflects the fact that the components of the wave vectors of the incident and scattered waves parallel to the fiber axis are equal to each other: k (in) ∥ = k (out) ∥ = ω c cosψ. (5) Since the absolute values of the wave vectors k(in) and k(out) are also equal, the angular distribution of the scattered radiation has the shape of empty cone with the half-opening angle equal to the incidence angle ψ of the wave to the fiber. Such a behavior permits de- scriptive interpretation: the incident wave produces a perturbation in the fiber that moves along the fiber with the velocity c/ cosψ. This superluminal motion generates the radiation analogous to Cherenkov one. Similar effect is described, particularly, in [4], where the radiation arising during the incidence a wave of dielectric permittivity of a substance (exited by the laser pulse) on the uniform charged fiber is consid- ered. The second term in the factor 1+c2(k (out) z )2/ω2 in (4) leads to the azimuthal asymmetry of the scatter- ing cross section. This asymmetry is negligibly small for small angles of incidence ψ ≪ 1, and the scatter- ing becomes isotropic over azimuth angle in respect to the fiber axis. Hereafter we shall neglect the az- imuthal asymmetry and put 1 + c2 ( k(out)z )2 /ω2 ≈ 2. (6) The account of the finite thickness of the fiber leads to the increase of the azimuthal asymmetry [5]. 3. KINETICS OF THE RADIATION PROPAGATION THROUGH THE ROPE OF PARALLEL FIBERS Consider now the scattering of the radiation inci- dent on the system of parallel fibers (rope) randomly arranged in the plane transverse to the fiber axis (Fig. 2). Evolution of the radiation intensity angular distribution during the propagation along such fiber should be described by a kinetic equation analogous to one describing the multiple scattering of particles in amorphous medium [6]. However, our problem is more complicated because of dependence of the scat- tering cross section on the fiber not only on the scat- tering angle (in respect to the direction of incidence), but also on the direction of incidence itself (in respect to the fiber axis). So, the dependence of the radiation intensity I on the z coordinate would be described by the kinetic equation ∂ ∂z I(ϑ, z) = (7) = ns L ∫ [I(ϑ− χ, z)dσ(ϑ− χ,χ)− I(ϑ, z)dσ(ϑ,χ)], where ϑ is the 2-dimensional angle that describes the radiation propagation direction in respect to the z axis, dσ(ϑ,χ) cross section of the wave scattering to the 2-dimensional angle χ from the initial direction ϑ, ns is the number of fibers per unit cross section of the rope. The first term in the right-hand side of (7) describes the income of the radiation intensity in the direction ϑ because of scattering off the direction ϑ−χ on the angle χ. The second term describes the outcome of the radiation intensity in the direction ϑ because of the scattering off that direction. Fig.2. The rope of straight fibers; the initial wave propagates along the z axis However, it is convenient to re-write the kinetic equa- tion (7) in slightly different form in order to use the cross section (4) specifics, when only the azimuthal scattering around the fiber axis takes the place. Let us re-write the cross section (4) with (6) in the form σ(θ(in),θ(out)) = 1 L dσ d2θ(out) = (8) = 2πr20n 2 e c ω δ ( cos θ(in) − cos θ(out) ) , where θ is the 2-dimensional angle that describes the radiation propagation direction in respect to the fiber 116 axis. Introducing the spherical coordinates d2θ′ = sin θ′dθ′dϕ and integrating over the polar angle θ′ us- ing the delta-function in (8), we obtain the kinetic equation that takes into account the azimuthal char- acter of the wave scattering on the fiber: ∂ ∂ξ I(θ, φ, ξ) = (9) = ns ∫ π −π [I(θ, φ− ϕ, ξ)σϕ(θ)− I(θ, φ, ξ)σϕ(θ)] dϕ, where the azimuthal angle ϕ is referenced from the incident wave azimuth, and the azimuthal scattering cross section σϕ(θ) ≈ 2πr20n 2 ec/ω (10) in our approximation depends neither on the angle of incidence θ nor on the azimuthal scattering angle ϕ. However, the equation (9) remains valid in general case. Azimuthal isotropy of the cross section (10) per- mits the further simplification of the kinetic equation (9): ∂ ∂ξ I(θ, φ, ξ) = (11) = nsσϕ ∫ π −π [I(θ, φ− ϕ, ξ)− I(θ, φ, ξ)] dϕ. The integration of the second term in the right-hand side of the equation gives the factor 2π, and the inte- gration of the first term leads to azimuthal averaging of the radiation intensity for the given θ. So, ∂ ∂ξ I(θ, φ, ξ) = −2πnsσϕ { I(θ, φ, ξ)− ⟨I(θ, φ, ξ)⟩φ } , (12) where ⟨I(θ, φ, ξ)⟩φ = 1 2π ∫ π −π I(θ, φ, ξ) dφ. Let us rewrite the kinetic equation (12) in the finite-difference form: I(θ, φ, ξ +∆ξ) = I(θ, φ, ξ)− (13) −∆ξ · 2πnsσϕ { I(θ, φ, ξ)− ⟨I(θ, φ, ξ)⟩φ } . Equation(13) demonstrates that the evolution of the intensity distribution happens as follows: the initial intensity is weakened by the factor (1−∆ξ · 2πnsσϕ) at every step ∆ξ along the fiber, but at the same time for every value of the angle θ the azimuthal symmet- rical “ring” (proportional to the average intensity for the given θ) is added to the existing intensity. So, the initial distribution with the shape of a sharp peak directed under the angle ψ to our fibers gradually transforms into the ring of the radius ψ in the space of angles. This behavior is illustrated by Fig. 3 where the evolution of the initial intensity distribution of Gaussian form I(θx, θy) = I0 exp[−((θx − ψ)2 + θ2y)/2σ 2], (14) (where θx = θ cosφ, θy = θ sinφ, σ is the disper- sion) is presented. The evolution had been simulated numerically using the finite differences equation (13). −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 0 θ x θ y I , a rb itr ar y un its −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 5 θ x θ y I , a rb itr ar y un its −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 10 θ x θ y I , a rb itr ar y un its −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 20 θ x θ y I , a rb itr ar y un its −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 30 θ x θ y I , a rb itr ar y un its −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 50 θ x θ y I , a rb itr ar y un its Fig.3. Evolution of the initial intensity distribution (14) with the dispersion σ = 0.001 and the angle of incidence ψ = 0.005 during propagation along the rope of straight fibers for the depths ∆ξ · t, where t = 0, 5, 10, 20, 30, 50. Coordinate step is ∆ξ = 0.1/2πnsσϕ, the direction of the fibers corresponds to the angles θx = θy = 0 117 Fig.4. The rope of bent fibers; the initial wave propagates along the fibers The finite differences equation (13) permits to investigate the evolution of the radiation inten- sity under propagation in the smoothly bent rope. Our approach is similar to the so-called split op- erator method used for numerical solution of the time-dependent Schrödinger equation (see, e.g., [7]). Namely, the azimuthal scattering around the current direction of the fibers on the small part of the rope according to the finite-difference formula (13) is al- ternated with the changing the direction of the fibers for the given value. Let us consider the rope bent in the plane (x, z) by the constant angle α per each step ∆ξ along the rope (Fig. 4). The initial distribution I(ϑx, ϑy) is described by the Gaussian function of the form (14) with the angles ϑx and ϑy referenced from the di- rection of the fixed axis z as arguments, in contrast to the case of the straight rope considered above. Let the maximum of the initial distribution coincides with the local direction of the fibers. The results of simulation of the evolution of that initial distribution are presented on Fig. 5; the rope bent per every step ∆ξ is α = 0.0002. We see that along with the significant spreading of the angular distribution the drift (shift of the maximum of the distribution) following the rope bent. So the con- ditions under which the rope “leads” the radiation after its bent are possible. −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 0 ϑ x ϑ y I , a rb itr ar y un its −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 20 ϑ x ϑ y I , a rb itr ar y un its −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 30 ϑ x ϑ y I , a rb itr ar y un its −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 40 ϑ x ϑ y I , a rb itr ar y un its −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 50 ϑ x ϑ y I , a rb itr ar y un its −0.01 0 0.01 −0.01 0 0.01 0 1 2 t = 60 ϑ x ϑ y I , a rb itr ar y un its Fig.5. Intensity distribution for the radiation propagating in the bent rope (Fig. 4) for the distances ∆ξ · t along the rope, where t = 0, 20, 30, 40, 50, 60; the coordinate step ∆ξ is the same as on Fig.3. The position of the maximum for t = 0 coincides with the local direction of the fibers axes 4. CONCLUSIONS The scattering of the electromagnetic wave under its oblique incidence on the linear string of charges is considered. The condition of validity of the approxi- mation of the uniform fiber for that string is found. The scattering in the last case would happen only in the directions making the same angle with the fiber axis as the incidence angle. In the specific case of the small angle of incidence and the infinitely thin fiber the scattering cross section would possess the azimuthal symmetry around the fiber axis. The cross section obtained is used for constructing the kinetic equation that describes the multiple scat- tering of the radiation in the system of parallel fibers (rope). The numerical procedure that simulates the wave propagation in the smoothly bent rope based on the finite difference form of the kinetic equation is developed. The existence of the conditions under which the maximum of the radiation angular distri- bution drifts following the rope bent is demonstrated. 118 ACKNOWLEDGEMENTS The work was supported by the Ministry of Educa- tion and Science of the Russian Federation (the State assignment N 3.500.2014/K). References 1. A.D.Pryamikov, A.S. Biriukov // Physics- Uspekhi. 2013, v. 56 (8), p. 813. 2. J.D. Jackson. Classical Electrodynamics. N.-Y., Wiley, 1998. 3. N.F. Shul’ga, V.V. Syshchenko, N.V. Soboleva // Poverhnost’. Rentgenovskie, sinhrotronnye i neytronnye issledovaniya. 2009, N11, p. 83 (in Russian). 4. V.A.Davydov, Yu.V.Korobkin, I.V.Romanov // JETP. 1994, v. 78 (6), p. 844. 5. N.F. Shul’ga, V.V. Syshchenko // Phys. Lett. 2003, v.A 313, p. 307. 6. H.Bethe // Phys. Rev. 1953, v. 89 (6), p. 1256. 7. M.D. Feit, J.A. Fleck, Jr.A. Steiger. // J. Com- put. Phys. 1982, v. 47, p. 412. ÐÀÑÑÅßÍÈÅ ÝËÅÊÒÐÎÌÀÃÍÈÒÍÎÉ ÂÎËÍÛ ÍÀ ÄÈÝËÅÊÒÐÈ×ÅÑÊÎÉ ÍÈÒÈ È ÑÈÑÒÅÌÅ ÏÀÐÀËËÅËÜÍÛÕ ÍÈÒÅÉ Í.Ô.Øóëüãà, Â.Â.Ñûùåíêî Ðàññìîòðåíî ðàññåÿíèå ïëîñêîé ýëåêòðîìàãíèòíîé âîëíû íà íèòåâèäíîé ìèøåíè. Ïîëó÷åííîå âûðà- æåíèå äëÿ ñå÷åíèÿ ðàññåÿíèÿ èñïîëüçîâàíî ïðè ïîñòðîåíèè êèíåòè÷åñêîãî óðàâíåíèÿ, îïèñûâàþùåãî ðàñïðîñòðàíåíèå âîëíû â ïó÷êå ïàðàëëåëüíûõ íèòåé. Ðàññìîòðåíà ýâîëþöèÿ èíòåíñèâíîñòè èçëó÷å- íèÿ, ðàñïðîñòðàíÿþùåãîñÿ â ïó÷êå ïðÿìûõ è èçîãíóòûõ íèòåé. ÐÎÇÑIßÍÍß ÅËÅÊÒÐÎÌÀÃÍÈÒÍÎ�I ÕÂÈËI ÍÀ ÄIÅËÅÊÒÐÈ×ÍIÉ ÍÈÒÖI ÒÀ ÑÈÑÒÅÌI ÏÀÐÀËÅËÜÍÈÕ ÍÈÒÎÊ Ì.Ô.Øóëüãà, Â.Â.Ñèùåíêî Ðîçãëÿíóòî ðîçñiÿííÿ ïëîñêî¨ åëåêòðîìàãíèòíî¨ õâèëi íà íèòåâèäíî¨ ìiøåíi. Îòðèìàíèé âèðàç äëÿ ïå- ðåðiçó ðîçñiÿííÿ âèêîðèñòàíî äëÿ ïîáóäîâè êiíåòè÷íîãî ðiâíÿííÿ, ùî îïèñó¹ ðîçïîâñþäæåííÿ õâèëi ó ïó÷êó ïàðàëåëüíèõ íèòîê. Ðîçãëÿíóòî åâîëþöiþ iíòåíñèâíîñòi âèïðîìiíþâàííÿ, ùî ðîçïîâñþäæó¹òüñÿ ó ïó÷êó ïðÿìèõ òà âèãíóòèõ íèòîê. 119
id nasplib_isofts_kiev_ua-123456789-80494
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
issn 1562-6016
language English
last_indexed 2025-12-07T16:25:09Z
publishDate 2014
publisher Національний науковий центр «Харківський фізико-технічний інститут» НАН України
record_format dspace
spelling Shul'ga, N. F.
Syshchenko, V. V.
2015-04-18T14:53:40Z
2015-04-18T14:53:40Z
2014
Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers/ N. F. Shul'ga, V. V. Syshchenko// Вопросы атомной науки и техники. — 2014. — № 5. — С. 115-119. — Бібліогр.: 7 назв. — анг.
1562-6016
PACS: 41.20.Jb, 42.25.Bs, 42.25.Fx, 42.81.-i
https://nasplib.isofts.kiev.ua/handle/123456789/80494
The scattering of the plane electromagnetic wave on the fiber-lake target is considered. The formula for the scattering cross section is used for building the kinetic equation that describes the propagation of the wave in the beam of parallel fibers. The evolution of intensity of the radiation propagating in the beam of straight and bent fibers is considered.
Рассмотрено рассеяние плоской электромагнитной волны на нитевидной мишени. Полученное выражение для сечения рассеяния использовано при построении кинетического уравнения, описывающего распространение волны в пучке параллельных нитей. Рассмотрена эволюция интенсивности излучения, распространяющегося в пучке прямых и изогнутых нитей.
Розглянуто розсiяння плоскої електромагнитної хвилi на нитевидної мiшенi. Отриманий вираз для перерiзу розсiяння використано для побудови кiнетичного рiвняння, що описує розповсюдження хвилi у пучку паралельних ниток. Розглянуто еволюцiю iнтенсивностi випромiнювання, що розповсюджується у пучку прямих та вигнутих ниток.
The work was supported by the Ministry of Education and Science of the Russian Federation (the State assignment N 3.500.2014/K).
en
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
Вопросы атомной науки и техники
Электродинамика
Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers
Рассеяние электромагнитной волны на диэлектрической нити и системе параллельных нитей
Розсiяння електромагнитноi хвилi на дiелектричнiй нитцi та системi паралельних ниток
Article
published earlier
spellingShingle Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers
Shul'ga, N. F.
Syshchenko, V. V.
Электродинамика
title Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers
title_alt Рассеяние электромагнитной волны на диэлектрической нити и системе параллельных нитей
Розсiяння електромагнитноi хвилi на дiелектричнiй нитцi та системi паралельних ниток
title_full Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers
title_fullStr Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers
title_full_unstemmed Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers
title_short Electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers
title_sort electromagnetic wave scattering on a dielectric fiber and a system of parallel fibers
topic Электродинамика
topic_facet Электродинамика
url https://nasplib.isofts.kiev.ua/handle/123456789/80494
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AT syshchenkovv rasseânieélektromagnitnoivolnynadiélektričeskoinitiisistemeparallelʹnyhnitei
AT shulganf rozsiânnâelektromagnitnoihvilinadielektričniinitcitasistemiparalelʹnihnitok
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