Research To The Reconstruction Approach For Central Dark Region Of Annular-beam Output Of Optical Unstable Resonator

Unstable resonator has a huge advantage in high power and high beam quality laser beam.However, conventional unstable resonators usually output circular beam, which limits itspractical application. In this thesis, the reconstruction approach for central dark region ofannular-beam output of unstable resonator is researched. We propose a novelty beam-shapingsystem for the reconstruction of dark region of annular-beam output of optical unstableresonator and investigated the effect of beam-shaping system theoretically and experimentally.Firstly, we research the the eigenmode behavior and output properties of positive branchconfocal unstable resonator theoretically through the eigenvetor method; According to the resultof the research above, we designed a positive branch confocal unstable resonator, the putputbeam of which has single mode and near-plane wavefront distribution. Secondly, we propose anovelty annular beam shaping system, which is composited by an inner cone annular scraper andan outer cone reflector; The realization principle and optical design method of the annular beamshaping system is introduced; We designed an annular beam shaping system, which cantransform the annular beam outputted by the positive branch confocal unstable resonator wedesigned to solid circular beam. Thirdly, on the basis of the positive branch confocal unstableresonator and the annular beam shaping system we designe above, the propagation propertiesand beam quality of the output beam passing through such shaping system are theoretieallyinvestigated, then, we compare it with the annular beam; The results show that the M~2factor ofthe shaped solid circular beam is1.18, which rise4.52times compared to the original annularbeam.At last, we research the propagation properties and beam quality of the output beam passingthrough such shaping system experimentally; After analysissing the data we get in theexperiment, we can conclude that the M~2factor of the shaped solid circular beam is3.2.In summary, the novelty annular–beam shaping system we propose can improvetransform annular beam to solid laser beam of high power and high beam quality.