A Study On Partially Coherent Hollow Beam And Caustic Beams

In this thesis,we mainly research on the construction and optical properties of partially coherent field related to the hollow beams and caustic beams.Some novel experiments to generate hollow beams and caustic beams are proposed.Meanwhile the effect of correlation property of partially coherent field on their propagation characteristics is fully discussed.In addition,two aspects of research works about the self-healing properties of hollow beams and spectral characteristics of caustic beams have been done.The main contents of this research are:1.we propose how to generate the periodic Bottle beam by using partially coherent beam.Firstly,a spatially complete coherent beam is transformed into a partially coherent beam by using the rotating ground glass.Secondly,after passing through the double axicon system,the parallel beam is converted into two Bessel beams which have the same optical frequencies but different radial wave vectors.Finally,the partially coherent periodic Bottle beam is generated by two interfering Bessel beams.Both the wave interference theory analysis and the experiment results show that the obtained Bottle beam is with the period of 2.5mm.By further investing the impact of field coherence on periodic Bottle beam in simulation and experiment,the intensity contrast ratio between the dark focus and surrounded regions of the periodic can be reduced with the decrease of spatial coherence degree.In this case,the period of Bottle beam and the central dark focus size will not be affected.2.The line focusing properties of axicon illuminated by J0-correlated Schell-model(JSM)beam are investigated.Results show that a hollow beam can be generated by focusing JSM with an axicon,and the size of hollow beams increases with the propagation distance.It is also shown that this class of dark hollow beams has the property of self-reconstruction when obstructed by an opaque obstacle.Based on the line focusing characteristics of axicon,a novel technique to generate precisely sizecontrolled hollow beams by controlling the diameter of circular slit is proposed.Result shows that,the proposed optical system generates a partially hollow beam,and the size of the hollow beam expands with the diameter of circular slit increasing.Therefore,the size of hollow beams can be precisely generated and controlled by the proposed system so that the optical system can be flexibly employed in optical trapping and manipulation of particles with different sizes.The results may provide a powerful tool for manipulating the micro-and nano-particles.3.The generation method and spatial correlation properties of partially coherent caustic beam are studied.Based on the cross-spectral density function and FresnelKirchhoff integral theory,the analytic expression of partially coherent caustic beam is derived.The influence of astigmatism introduced by tilted axicon at various angles on partially coherent caustic beam with respect to the propagation axis is studied theoretically and experimentally.Before further investigating the effect of field coherence on the partially coherent caustic beam,we also calculate the intensity distribution of light intensity in the images and spot diagrams in different spatial coherent lengths.Results show that the intensity contrast ratio between light focus and the surrounding dark regions can be reduced with the decrease of the spatial coherent lengths.In this case,the focus size of diffraction pattern will decrease as well.4.Partially coherent caustic beams are generated by quasi-monochromatic lightemitting diodes(LED)in experiment.It's shown that caustic beam also can be achieved by the focusing partially coherent LED light with a titled axicon.Before investigating the effect of astigmatism of axicon on caustic beam,we measured the distribution of light intensity of caustic beam along propagation distance in different tilted axicon situation.Results show that the characteristics of caustic beam can be influence by tilted axicon and propagation distance.In addition,the spectral characteristic of caustic beam is discussed with different quasi-monochromatic LED light.