Study On The Propagation And Scattering Property Of The Bessel Beams

The transverse intensity distribution of Bessel beams consist ofa central bright spot surrounded by a series of concentric rings. TheBessel beams that can be realized physically have finitenondiffractign propagation range. In the nondiffracting propagationrange, the Bessel beams keep their transverse intensity profileunchanged in their nondiffracting propagation range and canreconstruct their initial transverse intensity profile duringpropagation even disturbed by nontransparent obstacles. Thepropagation properties and the intensity profile characteristics ofthe Bessel beams make them useful in many optical applications suchas optical imaging, microfabrication, optical interconnection andalignment, particle manipulation, microlithography, nonlinearoptics. It is of interest to investigate further the propagationproperties of the Bessel beams for their applications.The propagation property of Super-Gaussian Bessel (SGB) beams inturbulent atmosphere is investigated. Based on the generalHuygens-Fresnel principle, the optical field distribution of SGB beamsin turbulent atmosphere is derived. The optical intensity on the axisand that on the cross section are numerically simulated. The comparisonwith the optical field distribution of SGB beams in vacuum show thatthe nondiffracting propagation distance of SGB beams is changed. Butsome SGB beams can still maintain their central spots with constantsize and intensity to some extent, being less disturbed whenpropagating in the atmosphere. In wireless laser communication, if wesubstitute SGB beams for Gauss beams, it is of actual significance toimprove the utilization ratio of light energy and simplify thestructure of the optical signal receiving system.Based on the Generalized Lorenz-Mie Theory (GLMT), the scatteringproperty of unpolarized Bessel beams by a sphere is investigated. Theanalytical scattering field solutions of ideal unpolarized Bessel beams by a sphere are derived by means of the spherical vector wavefunctions expansion, after which the dimensionless scatteringfunction as well as the scattering cross section and extinction crosssection is obtained. The dimensionless scattering function isapplicable to spherical scatterers of any size and refractive indexat any position in unpolarized Bessel beams. Numerical simulation ofthe dimensionless scattering function shows that for the on-axisspherical scatterers, the scattering profiles depend on the ratiobetween the size of the spherical scatterers and the central spot sizeof the Bessel beam；for the larger spherical scatterers, the scatteringextreme points exist in the direction or the neighboring direction ofthe conical angle of the Bessel beam, which can be explained betterby the quantum theory of light；for off-axis scatterers, the scatteringextreme points lie in the plane determined by the spherical scatterercenter and the beam axis.Similarly, Based on GLMT，by means of Fourier transform, planewaves spectrum expansion and the spherical vector wave functionsexpansion, the scattered field of unpolarized Bessel-Gauss beams isalso investigated. Comparison of the scattering far field with thatof the ideal unpolarized Bessel beams show that the finite beam widthchanges the relative intensity of the scattering extreme points, butalmost has no effects of the directions that the scattering extremepoints exist in for the off-axis spherical scatterers. Theexperimental result is in accordance with that of the numericalsimulation about the scattering near field, which proves thederivation correct about the scattering field of unpolarized Besselbeams by a sphere. The studies of the particle scattering property helpin understanding new physical phenomena or in designing new particlediagnostics systems. The scattering property investigation of Besselbeams make it promising to apply Bessel beams to Particle MeasurementTechnology.