Thermally-controlled laser-mode conversion based on spatially tunable photonic bandgap cholesteric liquid crystal templates

  • 林 星玗

Student thesis: Master's Thesis

Abstract

A spatially tunable dye-doped liquid crystal (DDLC) refilling cholesteric liquid crystal (CLC) polymer template device with a thermally controlled laser-mode conversion is successfully developed in this study This laser device is fabricated through four stages: before curing after curing after washing out and after refilling Experimental results show that the tunable spectral range for the photonic bandgap (PBG) of the laser device covers nearly the entire white region (405 nm to 752 nm) The spatially tunable laser mode can be converted between random lasing operation at low temperatures and bandedge lasing operation at high temperatures The mismatch between the refractive indices of the refilling nematic LC (NLC) in the nanopores and the template leads to multiple scattering of pumped fluorescence emission and to random lasing After the refilling LCs become isotropic the index match between the LC and the template causes the PBG of the template to appear and results in bandedge lasing emission The refilling template laser fabricated by forming a gradient-pitched CLC through nature diffusion has many drawbacks including the formation of defects relatively high energy threshold wide linewidth narrow tunable spectral range and long processing time The experimental results show that the structural and lasing features of the gradient-pitched refilling CLC template laser improve if rapid thermal annealing is repeatedly adopted during thermal diffusion particularly the ultralow energy threshold of 60 nJ/pulse The developed device has many advantages such as having a highly stable and defect-free structure an ultralow lasing threshold and wide spatial tunability and lasing-mode convertibility Hence the device has high application potential in photonics and display
Date of Award2014 Aug 25
Original languageEnglish
SupervisorChia-Rong Lee (Supervisor)

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