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Study On The Interaction Of Laser Shaped Beam With Spheroidal Particle

Posted on:2015-07-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:L HanFull Text:PDF
GTID:1108330464968914Subject:Optics
Abstract/Summary:PDF Full Text Request
With the development of laser optics, more and more beams of different shapes and profiles have been applied to the optical instruments. The interactions of laser shaped beam wave with particles have always been an important and hot international research topic, of current research interest with applications occurring in a variety of areas. As one of the non-spherical particles, the spheroid provides first order appropriate model in many practical situations. Generalized Lorenz-Mie theory(GLMT) is effective in describing the interaction between an arbitrarily shaped beam and a class of scatterer exhibiting a regular surface. It proves to be a complete and exact solution to Maxwell’s equations and can serve as rigorous theoretical basis for optical particle characterization. This thesis contributes to the development of a systematic rigorous theory to describe the shaped beam scattering by a spheroid. The main work and results are as follows:1. On the basis of the GLMT, this thesis presented a solution to the evaluation of beam shape coefficients in spheroidal coordinates by using an intrinsic method. Intrinsic methods evaluate beam shape coefficients of a GLMT posed in a certain coordinate system in terms of quantities pertaining to the same coordinate system. The determination of the spheroidal beam shape coefficients is carried out by expanding the incident beam in terms of spheroidal vector wave functions and using the the expressions of spheroidal vector wave functions.2. The intrinsic method of the beam shape coefficients of Gaussian beam in spheroidal coordinates is discussed. The fifth-order Davis-Barton beam and localized beam model are adopted to describe the incident Gaussian beam, respectively. Through the comparisons of spheroidal beam shape coefficients calculated by the intrinsic method with those computed by the extrinsic method, small differences are found, which could be taken as a sign that the numerical results are stable. Utilizing the tangential continuity of the electromagnetic fields, the expression coefficients of scattered and internal fields are determined. The numerical values of the far-field scattered intensity under Gaussian-beam illumination for dielectric spheroids with different parameters are given.3. A solution to the evaluation of spheroidal beam shape coefficients of the zero-order Bessel beam by using an intrinsic method is presented. Once the spheroidal beam shape coefficients are determined, the solution of scattering for a zero-order Bessel beam by a dielectric spheroid is obtained by means of the method of separation of variables. Numerical results concerning scattered field in the far zone are displayed for various parameters of the incident electromagnetic beam and of the scatter.4. Distributions of internal, near-surface and internal fields of a spheroid illuminated by a focused Gaussian beam are analyzed. The dielectric spheroids can squeeze light and enhance laser intensity on the shadow side. The high-intensity optical flux with rather narrow transverse dimensions and very low divergence angle does not just exist in very close vicinity to the surface of the particle but stretches beyond. The simulation results show that, by properly selecting the optical properties of particulate material and the particle geometry, it is possible to obtain the optical flux that can maintain a subwavelength full width half-maximum transverse beam width along a path. The influence of the waist radius of the incident Gaussian beam on the fluxe generated by the silica spheroid is discussed.5. Within the framework of GLMT, The spatial distributions of internal and near-surface field of a spheroid illuminated by a zero-order Bessel are analyzed. The effects on the field distributions from various parameters of the spheroid and zero-order Bessel beam, such as half-cone angle of the incident beam, major axis, minor axis and refractive index of the spheroid, are analyzed. This study would contribute to the understanding of Bessel beam scattering by nonspherical particles with sizes close to the incident wavelength.
Keywords/Search Tags:Electromagnetic scattering, Generalized Lorenz-Mie theory, Shaped Beam, Beam Shape Coefficients, Spheroidal particle
PDF Full Text Request
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