掺染料PVA分散液晶薄膜的制备研究

论文总字数：23200字

摘 要

激活无序增益介质后产生的谱线宽度窄化，以及明显阈值现象的激光辐射称之为随机激光，随机激光的光学反馈由多重散射提供。液晶是一类特殊的光学材料，液晶可以为光提供散射，从而使得液晶成为随机激光的一种散射介质。基于染料PVA分散液晶制备的乳液，其具有的可涂覆性以及能形成柔性薄膜激光器，使其在显示、图像处理等方面有潜在的应用价值。

本文研究了染料PVA分散液晶薄膜的厚度，染料液晶浓度对样片随机激光的影响，并确定掺染料PVA分散液晶薄膜样片制备的最佳条件。结果表明当染料液晶浓度保持7.7wt%不变，薄膜厚度从15μm增加到72μm，在38μm时，阈值最小（4.6μJ/pulse）、强度最大（50μJ/pulse泵浦能量下为1.18×10⁶a.u.）。这主要是因为厚度的增加导致染料分子数与液晶分子数的增加，进而导致泵浦效率与散射强度呈现出先增加后趋于饱和的趋势。另外，随着厚度的增加，在染料重吸收作用下，随机激光峰值波长出现4.6μm红移。样片厚度保持38μm不变，染料液晶浓度从3.85wt%增加到15.4wt%,阈值从6.9μJ/pulse减小到3.4μJ/pulse，50μJ/pulse泵浦能量下强度从1.06×10⁶a.u.增加到1.71×10⁶a.u.，这主要是因为染料液晶浓度的增加导致染料浓度以及液晶浓度的增加，进而导致泵浦效率与散射强度的增加，由于泵浦效率、散射强度与阈值成反比，因此最终导致阈值随着染料液晶浓度的增加而降低。同时在染料重吸收效应作用下峰值波长出现5nm红移。本文的研究内容有助于生产低成本低阈值高强度的柔性随机激光器件。

关键词：随机激光；向列相液晶；多重散射；聚乙烯醇；柔性

The preparation of Dye-Doped Polyvinyl-Alcohol Dispersed Liquid Crystals Films

Abstract

The random laser is a kind of laser emission with narrow line width and apparent threshold in an active random medium. The optical feedback is provided by multiple scattering. The liquid crystal(LC) is a special optical material which can provide scattering for the light, this property enables LC to be a scattering material for random laser. Dye-doped polyvinyl-alcohol(PVA) dispersed LCs emulsion could be paintable and able to fabricate flexible random laser device, so that it has the potential for display and image processing.

In this paper, the influence of the thickness of dye-doped PVA dispersed LC film and the concentration of dye-doped LCs to PVA on fluorescence and random lasing is studied and determine the best method to fabricate dye-doped polyvinyl-alcohol dispersed liquid crystals films. The results show that when concentration of dye-doped LCs remains 7.7wt% and with the increases of thickness from 15μm to 72μm, the lowest threshold(4.6μJ/pulse) of random laser, the highest intensity(1.18×10⁶a.u.) are obtained when the thickness of dry film is 38μm.That is because the number of dye and LC increases, this will makes the pump efficiency and the scattering strength increase and remain stable finally, because the the pump efficiency and the scattering strength is in inversely proportional to the threshold. Besides, with the increase of the thickness, the redshift of peak wavelength of the random laser happenes by 4.6nm because of the reabsorbtion of the dye; when the thickness remains 38μm and the concentraion of dye-doped LCs increases from 3.85wt% to 15.4wt%, the threshold decreased from 6.9μJ/pulse to 3.4μJ/pulse.The intensity of random laser increased from 1.06×10⁶a.u. to 1.71×10⁶a.u., this is because with the increase of the concentration of dye-doped LCs ,the concentration of dye and LCs increase which strengthen the pump efficiency and the scattering strength respectively, the the pump efficiency and the scattering strength is in inversely proportional to the threshold,so finally the threshold decrease with the increase of the concentration of dye-doped LCs. When the pump power is 50μJ/pulse , the redshift of peak wavelength happened by 5nm because of the reabsorbtion of the dye. This will help fabricating flexible random laser device with low cost and threshold, high intensity.

KEY WORDS:random laser, nematic liquid crystals, multiple scattering, PVA, flexibility

目录

摘 要 1

Abstract 1

第一章 绪 论 5

1.1 引言 5

1.1.1 课题背景 5

1.1.2 课题意义 5

1.2 聚合物分散液晶随机激光的研究现状 6

1.3 本文的研究目的与研究内容 11

第二章 聚合物分散液晶随机激光理论 12

2.1 随机激光研究的物理参量描述 12

2.2 随机激光的主要理论 12

2.2.1 随机增益介质光散射理论 12

2.2.2 非共振反馈与共振反馈 13

2.2.3 环形腔理论 13

第三章 掺染料PVA分散液晶薄膜制备 14

3.1 聚合物分散液晶随机激光样片制备 14

3.1.1 液晶乳液的制备 14

3.1.2 聚合物分散液晶随机激光样片的制备与涂布工艺的改进 15

3.2 验证样片出射随机激光 16

3.2.1 对比样片的制备 16

3.2.2 样片的透射特性以及荧光谱线对比 16

3.2.3 实验光路 17

3.2.4 样片的出射随机激光谱线对比 18

3.3 本章小结 18

第四章 薄膜厚度以及染料液晶浓度对出射随机激光特性的影响 19

4.1 样片厚度对出射随机激光的影响 19

4.1.1 样片制备 19

4.1.2不同厚度样片出射谱线对比 19

4.1.3 染料液晶浓度对随机激光的影响 21

4.2本章小结 23

第五章 总结与展望 25

5.1 总结 25

5.2 展望 25

致谢 26

参考文献 27

第一章 绪 论

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