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A Study on Propagation Properties of Partially Coherent Beams

Author: WuYunMei
Tutor: WangXiQing
School: Southwest Jiaotong University
Course: Optical Engineering
Keywords: Partially coherent beam Transmission characteristics Complex Gaussian function Nonparaxial transmission
CLC: O438
Type: Master's thesis
Year: 2007
Downloads: 272
Quote: 3
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Abstract


In recent years, partially coherent beam caused great interest in the study, partially coherent light source can produce laser-like far-field intensity distribution, intensity uniformity is better than a fully coherent laser beam. But this part of the research has focused on the Gaussian - Schell model (GSM) beam, the beam intensity distribution and the complex degree of coherence are Gaussian distribution. This article describes the other two types of new partially coherent light model that partially coherent modified Bessel - Gauss beam (MBGB) and the first class of zero-order Bessel - Schell model (JSM) beam study partially coherent optical transmission transform the basic theory and analysis methods. In practical applications, the transmission of the laser beam is often limited by the diaphragm, and therefore limited by apertures part of the coherent beam propagation characteristics MBGB and JSM research is necessary. However, when the beam has a larger angle of divergence or beam waist can be compared with the wavelength, the paraxial approximation is no longer valid. With the progress of the study of diode lasers, photonic crystals, micro-optics and micro-cavity laser, partially coherent beam transmission in nonparaxial areas within has attracted extensive attention, partially coherent nonparaxial beam of MBGB and JSM characteristics has important theoretical significance and practical value. The research work in this paper include: 1. On a partially coherent MBGB and JSM beam through paraxial optical ABCD system transmission hard aperture, using the hard-edged aperture function expansion method for a finite number of complex Gaussian functions and derive approximate analytical propagation equation. Free-space transmission, for example the partially coherent MBGB in the case of an Aperture numerical calculation, calculation error and the scope of analytical formulas obtained are discussed. The results show that the complex Gaussian function expansion method can be quickly studied analytically the partially coherent MBGB through the circular aperture free space transmission characteristics, analysis Fresnel number, the truncation parameter after the diaphragm of partially coherent MBGB after light intensity distribution impact. And JSM focusing properties of the beam through the circular aperture thin lens system are analyzed and discussed. The numerical results show that the relative focal shift, truncation parameter related with the Fresnel number. 2. Generalized Rayleigh diffraction integral formula and the theory of partially coherent light out the arbitrary order nonparaxial partially coherent MBGB and nonparaxial JSM beams in free space resolution transmission equation is derived. As a special case, given the nonparaxial partially coherent MBGB far-field formulas and paraxial part coherent MBGB transmission formula. Numerical calculation and analysis show that the f parameter of the partially coherent MBGB nonparaxial characteristics important; addition, the spectral degree of coherence parameter ξ also affect the beam nonparaxial behavior. Nonparaxial JSM beam nonparaxial JSM analytical propagation equations and the phase of the beam in the far-field and paraxial approximation analytical formulas. Research shows, f Parameters and f_β parameters on the JSM beam nonparaxial behavior f parameter influence the nonparaxial JSM beam of the phase distribution. 3. Under normal circumstances, the focal position of the focused light beam to define the axial intensity of the position of the maximum point. When the zero axis intensity axis intensity method loses its meaning, this time can be the ring circumference power law to discuss the focal plane of the beam position; Moreover, due to the non-planar waveguide factors, the focus position of the focal plane position not necessarily coincide. The view from practical application and the energy concentration is more reasonable to define the actual focal plane, the plane of the beam waist position (minimum spot size plane). Cosine - Gaussian beam, for example, the actual focal plane and its position on the beam are analyzed and discussed. In cosine - Gaussian beam through a thin lens focusing system based on the field distribution function using second-order moment defined export focus cosine - Gaussian beam spot function analytic expression thus obtained waist width and position, and then to analytical expression for the cosine - Gaussian beam relative focal shift. Parameters and beam parameters of the optical system of the actual focal plane position and made a numerical calculation.

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