Study On Partially Coherent Light And Its Spectrum Changes

The coherence, polarization and spectral properties of light field are topics of current interest, which play an important role in development of the modern optics theory and laser technologies. Starting from the propagation law of partially coherent light and using a typical partially coherent light, i.e., Gaussian Schell-model (GSM) beam describing the multimode laser in practice, I present in this dissertation the research results on vectorial partially coherent light, spectral changes of partially coherent light passing through optical element, spectral switch of partially coherent light diffracted by an aperture, and the spectral anomaly of diffracted fully spatially coherent light by an aperture.The basic concepts of second-order coherence theory in describing wavefields are introduced. These concepts are the cross-spectral density function and spectral degree of coherence in the space-frequency domain, and the mutual coherence function and the complex degree of coherence in the space-time domain. A comprehensive review of the basic analytical methods for the beam transformation including the matrix optics method, diffraction integral method and Wigner distribution function method is summarized. Finally several beam models for the partially coherent beam are introduced, which include GSM beam, polychromatic vector GSM beam and partially polarized Gaussian Schell-model (PGSM) beam et al. Based on the above theory and methods, the main works of this thesis are lasted as follows:Starting from the propagation law of partial coherent light and beam coherence-polarization (BCP) matrix approach, the properties of PGSM beams through both an axis-symmetric paraxial optical ABCD system and an axis-unsymmetric one are studied. The analytical propagation equations of PGSM beams are derived, which enable us to study the propagation-induced polarization changes and irradiance distributions of PGSM beams through an axis-symmetricparaxial optical ABCD system and an axis-unsymmetric one. Detailed numerical results for a PGSM beam passing through a bifocal lens are presented. It implies that the degree of polarization is no longer uniformly polarized in general andpropagation-induced polarization changes depend on the beam parameters and system parameters, such as beam coherence parameter. It is shown that the aperture affects the polarization and irradiance distributions of PGSM beams, and that the change of degree of polarization is not monotonous with the change of truncation parameter. A comparison of PGSM beams with scalar GSM beams has been given indicating that these two kinds of beams have similar irradiance profiles after passing through an isotropic ABCD system and an aperture. The central-dip beam profile occurs when a PGSM beam through optical ABCD system with a polarizer, but the beam profile of scalar GSM beam does not happen. It has been shown that irradiance distribution of a PGSM beam through an anisotropic polarizer is influenced by their vectorial properties.Based on the propagation law of the cross-spectral density function in the space-frequency domain, the properties of polychromatic vector GSM beamsthrough a paraxial optical ABCD system are studied. The analytical propagationexpressions for the cross-spectral density matrix of vector GSM beams passing through a paraxial optical ABCD system are derived, which permits us to study the propagation properties of vector GSM beams, including the propagation-induced polarization changes, effect of the spectrum bandwidth and irradiance distributions in a unique way. There are some applications of the theoretical results. As an example, polarization changes in vector GSM beams propagating through a telescopic system have been analyzed and illustrated by numerical results. It has been found that propagation- induced polarization changes are non-uniform across the beam cross-section. For the symmetric Gaussian spectrum, the effect of the bandwidth on the polarization is barely noticeable. There a...