摻染料高分子分散液晶在微管內之隨機雷射

本篇論文主要是研究在空心玻璃管內填入摻染料高分子分散液晶隨機雷射之特性研究，其中液晶混合物是由摻有雷射染料的向列型液晶混合物中加入不同濃度的單體(10 wt%, 20 wt% 與 30 wt% NOA65)製作而成，利用毛細現象將液晶混合物填滿空心玻璃微管，再利用紫外光曝曬此時單體也會轉變成為高分子聚合物，並將光學膠塗抹於空心玻璃微管的兩端;利用Q-開關 Nd:YAG 雷射作為泵激光源，並使用光譜儀收集摻染料高分子分散液晶隨機雷射的頻譜，在此雷射中除了利用液晶作為散射介質，由於高分子聚合物與液晶的折射率不同，使得空心玻璃微管內光散射的強度增加，因此發現在自發性輻射光譜上產生多根窄頻的雷射譜線，其中液晶混合物所激發雷射譜線的數量和線寬及雷射的臨界功率會受到單體的密度和大小所影響，由實驗發現在摻入20 wt%單體所得到隨機雷射的特性最明顯，當濃度再增加時由於散射損耗的增加，使得所得到輸出雷射譜強度降低；此外，我也研究摻入20 wt%單體高分子分散液晶隨機雷射在不同溫度下的特性，發現在較低溫度情況下，所激發的模態數目較多且雷射具有低的臨界功率，且計算得到Q因子的數值也較高，推究原因為低溫環境下，液晶的雙折射會大於高溫環境，因而造成玻璃微管內的散射強度增加。

關鍵字

隨機雷射；液晶；玻璃微管； PDLC

並列摘要

The resonance characteristics of random lasers from dye-doped polymer dispersive liquid crystals (DD-PDLCs) within capillary tubes are investigated. The DD-PDLCs were prepared by doping laser dye as the gain medium and mixed different concentration of monomer into the nematic liquid crystals. Then, the DD-PCLC mixtures were filled into the capillary tubes by the capillary effect and then exposed UV light to make the monomer solidify into a polymer. Through excitation by the Q-switched pulse, the emission spectra from the capillary tube revealed multiple emission spikes with narrower emission linewidth due to enhancement of the light scattering. Besides, the number of emission spikes, FWHM and lasing threshold from the DD-PDLCs were determined by the density and grain size of the polymer clusters within the PDLC mixtures through the alternation of the concentration of the doping monomer. Furthermore, the lasing performance of the DD-PDLCs in the capillary tube could be controlled by temperature. At a lower temperature, more emission spikes at longer wavelengths were excited, and the laser revealed a relatively high Q-factor accompanied with relatively low threshold pump energy owing to the increase in the birefringence of the liquid crystal molecules so that multiple recurrent light scattering would be efficiently enhanced.

並列關鍵字

Laser and laser optics ； Dye lasers ； Microcavities ； Multiple scattering

參考文獻

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摻染料高分子分散液晶在微管內之隨機雷射

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