A study on the characteristics of cylindrical vector polarization and nonlinear dynamics behavior in Nd-doped laser systems

Abstract

In this dissertation we have investigated the two characteristics of laser output in laser-diode-pumped Nd-doped laser systems that one is the generation of cylindrical vector beams under different cavity configuration and the other one is dynamical behaviors For our work the mechanism of producing cylindrical vector beams is based on the intrinsic characteristic of birefringence which is provided from laser crystal When the laser cavity was operated nearby the boundary of stable region the range in which the extraordinary ray (e-ray) is stable but the ordinary ray (o-ray) is unstable will be achieved and vice versa An intra-cavity axicon can generate the off-axis modes with ring or arc oscillation and enlarge the contribution of birefringence effect provided from the laser crystal When the laser cavity was increased the transformation of polarization state was observed This feature can be explained by using ray-tracing method for both rays Furthermore we offered the method that without inserted any optical elements to directly realize cylindrical vector beams in three-element cavity under the specific configuration Base on the round-trip ABCD transfer matrices and self-consistent q-parameter theboundary of stable region can be computed and analyzed under different cavity configurations The experimental results reveal that the transformations of polarization are observed by properly tuning cavity length from unstable to stable region The overlap integrals for the e-ray and the o-ray were calculated with the dependence of cavity length further concerning the extraction efficiency from pump energy The behavior of transforming polarization can be interpreted Further inserting the saturable absorber in the laser cavity the pulsed type of cylindrical vector beams can be demonstrated On the other hand we used the bottle shape which was formed with a combination of the axicon and the lens to excite the microchip laser It directly produces the cylindrical vector beams; however the thermal effect cannot be ignored For active type to generate cylindrical vector beams just a single element can be implemented in this setup In the study of the laser dynamics behavior we reshaped the pump modulation with dual waveforms in time sequences to investigate the suppression of chaos The first sinusoidal modulation with the specific conditions allows laser system to change the chaotic output The waveform of the second modulation was varied to be sinusoidal square and triangle We found that the suppression region was changed; therefore the modulated profile can be used as a parameter to control the dynamics In the chaos-suppressed route double phase locking was occurred when the modulation depth of the second modulation increased By numerical simulations the generalized Huygens diffraction integral with the round-trip ABCD matrix was employed to describe the propagation of the optical field The amplification of optical field through the gain medium can be calculated by using iterative method with the rate equation According to the different parameters the results of simulation and experiment were verified mutually The experimental results are consistent with the numerical simulations This part was the pure investigation of nonlinear dynamic behavior Finally we generated cylindrical vector beam from three-element cavity laser system and then adding single modulation to control its dynamic behavior The relationship between the spatial polarization characteristics and dynamic behavior in period-2 and chaos signal were further explored Furthermore we use the concept of linear superposition for qualitative analysis to successfully explain the observed experimental results I am responsible for constructing the simple simulation for this part We found that the dynamics behavior belongs to temporal chaos with the correlation between spatial and polarization The characteristics of spatial-polarization temporal dynamics should be further researched in detail

Date of Award	2014 Aug 6
Original language	English
Supervisor	Ming-Dar Wei (Supervisor)