Generation Of Fully Vectorial Optical Fields And Their Applications

With the rapid development of laser technology, information acquisition and processing with the help of polarized light plays a more and more important role in the modern scientific and technological research. To fully take the advantage of photon, which acts as the carriers of information, the key issue is how to manipulate the optical field. There exist two kinds of the modulation of optical field; one modulation is carried out in time domain and the other is in space domain. The parameters that can be modulated are frequency, amplitude, phase and polarization of light. The time domain modulation is to control the frequency of light and the space domain modulation aims at managing the amplitude, phase and polarization of light. In this thesis we focus our attention on the spatial modulation of light. With the development of optical technology, the methods that can be used to modulate amplitude and phase have been established well. However, the modulation of polarization remains to be challenging. Furthermore, the simultaneous modulation of phase, amplitude and polarization is much more complicated. Obviously, the complete shaping of the spatial parameters of light can help to discover more new optical effects and phenomena. In this thesis, we will make our efforts mainly on the generation of full vector fields and their application. The main issues addressed in this dissertation are as follows:1. A scheme to modulate the phase, amplitude and polarization simultaneously and independently is proposed. A vector beam generator which is based on the optical 4-f system and a spatial light modulator (SLM) is introduced. The principle of the generator is decomposition and recombination of optical beam. A beam of Gaussian laser light is changed into two orthogonal polarized base vector beams after passing through a SLM and a spatial filter. Then the base vector beams are recombined into a vector beam by a Ronchi grating. The former generator is subject to the ability of the SLM and it can only modulate the phase structure of the base vector beams. As a result, the former generator can merely control the phase and polarization structure of the generated vector beams and the state of the polarization can’t cover the full Poincare sphere but only a great-circle on Poincare sphere. In order to break the mentioned limitation, we use a phase-only method to encode the complex amplitudes of the two base vector beams. That’s to say, the phase and amplitude distribution of the two base vector beams can be tailored completely and then the spatial parameters of the vector beam composed by the two base vector beams can be controlled fully. The full-vector beam generation scheme proposed in this thesis is universally valid. We can decompose any specific vector field into two orthogonal polarized base vector fields and encode the base vector fields by the phase-only encoding method, then the vector field can be produced by the 4f system based vector beam generator. The feasibility and reliability of the proposed scheme is demonstrated by experiments.2. A solution to completely shaping the focal field is proposed. The main problem of focus shaping is to find the incident field corresponding with the focal field. There exist two kinds of widely used methods to solve this problem. One is forward design method, this is a tentative method and the structure of the incident filed is changed by experience to get the desired focal field. For the process of finding appropriate incident field is complicated and is suitable for some special focal field, the usage of the forward method is limited. Another method is iterative method. The iterative method is an approximate solution to the target field distribution and the convergence performance differs for different situations, depending on the constraint required by the target field; iterative search does not guarantee a satisfactory result in all cases. Another essential defect of iterative methods is that it is impossible to control the distribution of all the parameters in the focal field, as at least one parameter is assumed to be arbitrary during the iterative process. In addition, since iterative search and forward method are both time-consuming, they are not suitable for the real-time engineering of the focal field. In this thesis we propose a method that can be used to completely shaping the focal field. In this scheme, the incident field is obtained by inverse calculation of the focus process and the calculation is based on the Richards-Wolf vectorial diffraction theory and the transform matrix between the fields on the exit and entrance pupil of the objective lens. The inverse calculation can be implemented by the fast Fourier transform and chirp-z transformation to ensure the speed and accuracy of the inverse calculation. The inverse scheme need only one time calculation and there is no free parameters, so this method can be used to complete control the focal field in real time. The inverse design method is verified by experiments and we introduce a kind of "perfect polarization vortex field" and this kind field is generated using the inverse design method.3. A detection method based on sheer interferometry that can be used to determine the topological charge (TC) of phase vortex is proposed. This scheme can be used to detect the phase vortex TC of both scalar beam and vector vortex beam (VVB). A beam with phase or polarization vortex is divided into two orthogonal polarized beams by a parallel beam divider (PBD). The two beams have the same propagation direction and orthogonal polarizations. The centers of the two beams are mutually sheared through the PBD. The interference fringes of the two beams can reveal the absolute value and the sign of the TC of the phase and polarization vortex. In the situation of scalar beam phase vortex TC detection, the fork numbers around the two intensity singularity are the same and equal to the absolute value of the TC and the direction of the interference fringes give the information of the sign of TC. While in the situation of VVB phase vortex TC detection, the fork number around each intensity singularity is equal to the phase vortex TC of each component of the vector field respectively and the direction of the interference fringes give the information of the sign of phase vortex TC. From the phase vortices TC of the two orthogonal components of the vector beam with polarization vortex, the TC of polarization vortex can be calculated. In comparison to other detection methods, the merits of our scheme are obvious. The detection setup is independent of any optical beam generation system and it contains only four or five optical elements, it is very convenient to be built and used; there is no need to align the center of the vortex phase and the center of the optical elements, so the setup is very easy to be built and robust to the environment. In addition, both the absolute value and the sign of TC can be detected. The TC can be recognized by the image recorded by a CCD cameral or even by the naked eyes in some special cases. The optical elements used in the detection system allow high damage threshold, and consequently, our method can be used in high laser power situation. We also find that the proposed detection method are valid for both coherent and partial coherent light and the vortex TC detection scheme is tested by experiments.