Propagation Properties Of Beams With Amplitude And Phase Modulation

Propagation property of beam with amplitude and phase modulation has becomethe focus of investigation. Study on propagation properties of partially coherentbeams, vortex beams and high-order Bessel beams generated by amplitude or phasemodulation has attracted much attention because of the potential applications inInertial Confinement Fusion (ICF), optical communication and optical manipulationetc.In this dissertation, the intensity, the degree of coherence and degree of polarizationof partially coherent beams, vortex beams, and high-order Bessel beams generated byamplitude or phase modulation on propagation are studied in detail. We also studiedthe spatial coherence of high-power multi-chip red LEDs. The main research contentsare listed as follows:1. Based on the generalized Huygens–Fresnel diffraction integral and the unifiedtheory of coherence and polarization, properties of stochastic electromagnetic beamsfocused by a modulated lens are analyzed, the analytical expressions for thecross-spectral density matrix of a class of electromagnetic Gaussian Schell-model(EGSM) beams focused by an amplitude modulated lens are derived, and intensitydistribution of EGSM beams focused by an amplitude modulated lens throughnumerical calculations is also analyzed. It shows that focused intensity distribution ofEGSM beams is influenced by radius, location, transmittance of amplitudemodulation, spatial position and the coherence length. When the radius of amplitudemodulation takes a certain value, it appeares that focusing spot is extremelycompressed and focusing central spot has a large energy at this time. Different shapesof intensity distribution can be gotten by changing the parameters of radius, location,transmittance of amplitude modulations and spatial position, and the coherencelength.2. Based on the generalized Huygens–Fresnel diffraction integral and the unifiedtheory of coherence and polarization, propagation properties of partially coherentelectromagnetic square flat-topped pulsed beams with amplitude and phasemodulations in free space are analyzed. The analytical expressions for the cross-spectral density matrix of partially coherent electromagnetic square flat-toppedpulsed beams with amplitude and phase modulations in free space are derived, andthe numerical calculations are also given. It is shown that the spectral intensitydistribution of partially coherent electromagnetic square flat-topped pulsed beams isinfluenced by size of the modulation zone, the depth of amplitude and phasemodulations, the coherence length and temporal coherence length of the beams, andtransmission distance.3. We theoretically and experimentally investigate the Fraunhofer diffractionpattern of a vortex beam passing through an annular ellipse aperture. It is found thatthe pattern of the far-field diffraction intensity distribution exhibits some dark spots,which become clearer with increasing the value of the ellipticity factor of the annularellipse aperture. The diffraction phenomenon is more obvious with increasing thevalue of the ratio of the inner long axis (or short axis) to the outer side of the annularellipse aperture. The number of the dark spots in the Fraunhofer diffraction intensitydistribution is just equal to the topological charge value of the measured opticalvortex, and the centre of each dark spot is just a phase-singularity point. Based on thisproperty, we can measure the topological charge of an optical vortex beam.4. Based on the Fresnel-Kirchhoff diffraction theory, the diffraction effects ofhigh-order Bessel beams through the nonlinear optical media are analyzed, which canexplain the Z-scan phenomena of high-order Bessel beams. By comparing thenormalized Z-scan transmittances of Gaussian beam, zero-order Bessel beam,first-order Bessel beam, second-order Bessel beam and third-order Bessel beam, it isshown that Z-scan using the high-order Bessel beam has a higher sensitivity than thatusing the zero-order Bessel beam. The Z-scan with the high-order Bessel beams mayprovide a precise method for measuring the nonlinear coefficients of optical media.5. Based on the Van Cittert–Zernike theorem, we investigate the spatial coherenceof the light beam which radiated from the high-power multi-chip red LEDs. Thetheoretical calculation shows that the non-coherent light beam generated from themulti-chip single-color LEDs changed into partially coherent light after propagationand the spatial coherence improve with increasing propagate distance. In addition, itis found that the spatial coherence of the light beams is related to its chip architecture of the multi-chip LEDs. By double-slit interference we measure the spatial coherenceof the light beams experimentally. The experimental measurement of the spatialcoherence is consistent with the theoretical result.