胆固醇液晶激光效率提高研究

发布时间：2019-06-02 12:45

【摘要】：自从20世纪60年代激光器问世以来,激光器已经被广泛应用于通讯、生物、医学、国防、军事等领域,对人们的生活产生了革命性的变化。目前常用的激光器主要有固体激光器、气体激光器、染料激光器和半导体激光器等,它们都具有稳定性好的特点,但是它们的致命缺点是体积大,这使得它们越来越不能满足集成光学发展的需要。集成光学的发展越来越需要微型激光器,因此近年来微型激光得到了广泛的研究。目前被广泛研究的微型激光器主要有法布里-珀罗(F-P)腔激光器、分布式反馈激光器(FDB)、微腔激光器及碟片激光器等几种类型,这几类激光器都具有阈值低、体积小、光谱较窄、调制速率高等特点,但它们的制作工艺都非常复杂,有的需要高精度的镀膜技术,成本很高。胆固醇液晶(cholesteric liquid crystal,CLC)因其周期性螺旋结构和高双折射率的特点,会形成布拉格反射带,相当于一维光子晶体。与传统的光子晶体相比,胆固醇液晶具有很多独特的特点。首先胆固醇液晶反射带的中心波长和带宽很容易通过电场、磁场、温度等外界条件调控,因此可以很容易利用胆固醇液晶制备可调光学器件,比如可调光学滤波器、光开关等。其二是胆固醇液晶器件制备工艺非常简单,只需在液晶中参杂一些手性分子,然后灌入液晶盒中便可以获得周期性螺旋结构的胆固醇液晶。因为这些独特的特点,近年来胆固醇液晶引起广泛的研究兴趣,包括开发在柔性显示、光开关、可调光学滤波器等方面的应用。研究发现通过在胆固醇液晶中掺杂高发光效率的激光染料,可以在无需反馈腔的情况下获得激光输出。因为胆固醇液晶制备简单,这一发现引起了广泛的研究兴趣。人们对胆固醇液晶激光进行了大量的研究,所有这些研究大致可以归纳为两个方面：一方面是研究可调胆固醇液晶激光,另一方面是提高胆固醇液晶激光效率。尽管人们采取不同方法提高胆固醇液晶激光的效率,但是,到目前为止胆固醇液晶激光效率仍然不高,这严重制约了胆固醇液晶激光器的实际应用。为了使胆固醇液晶激光器最终能应用到实际中去,胆固醇液晶激光效率必须进一步提高,这正是本文研究的目标。为了提高胆固醇液晶激光效率,本文研究了胆固醇液晶分子排列,胆固醇液晶结构、厚度以及胆固醇液晶反射镜的加入对胆固醇液晶激光效率的影响及其物理机制。具体研究内容主要包括以下几个方面：1.研究了电击摩擦处理对胆固醇液晶分子排列的改善。研究表明随着液晶盒厚度的增加,其内部缺陷增多,透射率也相应降低,而采用电击摩擦方法处理可以明显改善分子排列。例如对于厚度大于25μm的胆固醇液晶样品,没经过任何处理之前,胆固醇液晶分子处于无序的焦锥状结构,透射率接近于0；经过电击摩擦处理后,样品变为平面螺旋结构,散射明显降低,样品透射率由处理之前的几乎为0提高到80%,且该方法制得的胆固醇液晶样品能够长期稳定保持其平面螺旋结构不变。本文分析了该现象背后的原因及其物理机制。2.研究了胆固醇液晶结构对胆固醇液晶激光效率的影响及其物理机制。研究表明经过电击摩擦处理后,胆固醇液晶激光阈值降低了,同时激光效率也得到了提高,且样品越厚,电击摩擦处理后激光效率提高得越多,比如5μm的染料掺杂胆固醇液晶样品经过摩擦处理后激光效率提高了1.6倍,而50μm染料掺杂的胆固醇液晶激光效率可以提高10.7倍。本文分析了该现象背后的原因及其物理机制。3.研究了用胆固醇液晶作为反射镜对胆固醇液晶激光效率的影响及其物理机制。采用与染料掺杂的胆固醇液晶同手性且带宽能够覆盖激光波长的胆固醇液晶作为反射镜,将其放置在染料掺杂的胆固醇液晶的一侧,结果表明,胆固醇液晶激光效率可以得到进一步提高,且提高的倍数随着染料掺杂胆固醇液晶厚度的增加而降低。本文分析了产生该现象的原因及其物理机制。值得一提的是,通过摩擦处理并加反射镜后,我们在10μm的激光样品中获得了最高达10%的激光效率,这是目前为止在胆固醇液晶中获得的最高激光效率。
[Abstract]:Since the advent of the laser in the 1960s, the laser has been widely used in the fields of communication, biology, medicine, national defense and military, and has revolutionized the lives of people. The most commonly used lasers are solid-state lasers, gas lasers, dye lasers and semiconductor lasers, all of which have the characteristics of good stability, but their fatal disadvantages are bulky, which makes them increasingly unable to meet the need for integrated optical development. The development of integrated optics is more and more need of micro-laser, so the micro-laser has been widely studied in recent years. There are several types of lasers, such as the Fabry-Perot (F-P) cavity laser, the distributed feedback laser (FDB), the micro-cavity laser and the disc laser, which have the characteristics of low threshold, small volume, narrow spectrum, high modulation rate and the like. But the manufacturing process is very complicated, and the high-precision coating technology is required, and the cost is high. The cholesteric liquid crystal (CLC), because of its periodic spiral structure and high birefringence, will form a Bragg reflector, which is equivalent to one-dimensional photonic crystal. Compared with the traditional photonic crystal, the cholesteric liquid crystal has a plurality of unique characteristics. The central wavelength and the bandwidth of the cholesteric liquid crystal reflection band are easily controlled by external conditions such as electric field, magnetic field, temperature and the like, so that the adjustable optical device can be easily prepared by using the cholesteric liquid crystal, such as an adjustable optical filter, an optical switch and the like. And the other is that the preparation process of the cholesteric liquid crystal device is very simple, only some chiral molecules are involved in the liquid crystal, and then the cholesteric liquid crystal with the periodic spiral structure can be obtained after being poured into the liquid crystal box. Because of these unique characteristics, in recent years, cholesteric liquid crystal has attracted extensive research interest, including the application of developing in flexible display, optical switch, tunable optical filter and so on. It has been found that the laser output can be obtained without the need for a feedback cavity by doping a laser dye with high luminous efficiency in a cholesteric liquid crystal. This finding, because of the simple preparation of cholesteric liquid crystals, has led to a wide range of research interest. A large number of studies have been carried out on the cholesteric liquid crystal laser, all of which can be summarized in two aspects: on the one hand, to study the cholesteric liquid crystal laser, on the other hand, to improve the efficiency of the cholesteric liquid crystal laser. Although the efficiency of the cholesteric liquid crystal laser is improved by different methods, the efficiency of the cholesteric liquid crystal laser is still not high so far, which seriously restricts the practical application of the cholesteric liquid crystal laser. In order to finally apply the cholesteric liquid crystal laser to the practical application, the efficiency of the cholesteric liquid crystal laser must be further improved, which is the aim of this paper. In order to improve the efficiency of cholesteric liquid crystal laser, this paper studies the effect of cholesteric liquid crystal molecule arrangement, cholesteric liquid crystal structure, thickness and the addition of cholesteric liquid crystal reflector on the efficiency of cholesteric liquid crystal laser and its physical mechanism. The specific research contents mainly include the following aspects:1. The improvement of the arrangement of cholesteric liquid crystal molecules by electric shock friction treatment was studied. The results show that with the increase of the thickness of the liquid crystal cell, the internal defect of the liquid crystal cell is increased, and the transmittance is correspondingly reduced, and the molecular arrangement can be obviously improved by using the electric shock friction method. for example, for cholesteric liquid crystal samples with a thickness of more than 25 & mu; m, the cholesteric liquid crystal molecules are in a disordered focal conic structure before any treatment, and the transmittance is close to zero; after the electric shock friction treatment, the sample is changed into a plane spiral structure, and the scattering is obviously reduced; The sample transmittance is increased by almost 0 to 80% before the treatment, and the cholesteric liquid crystal sample prepared by the method can stably keep the plane spiral structure unchanged for a long time. This paper analyzes the reasons behind this phenomenon and its physical mechanism. The effect of cholesteric liquid crystal structure on the efficiency of cholesteric liquid crystal laser and its physical mechanism were studied. The results show that the laser threshold of the cholesteric liquid crystal is reduced after the electric shock and the laser efficiency is improved, and the thicker the sample, the more the laser efficiency is improved after the electric shock is processed. For example, a dye-doped cholesteric liquid crystal sample of 5. m u.m is increased by 1.6 times by the rubbing treatment, and the efficiency of the 50 mum dye-doped cholesteric liquid crystal laser can be increased by 10.7 times. The reason behind this phenomenon and its physical mechanism are analyzed in this paper. The effect of cholesteric liquid crystal on the efficiency of cholesteric liquid crystal laser and its physical mechanism were studied. The cholesteric liquid crystal with the same chiral and bandwidth as the dye-doped cholesteric liquid crystal can cover the laser wavelength as a reflector, and the cholesteric liquid crystal is placed on one side of the dye-doped cholesteric liquid crystal, and the result shows that the efficiency of the cholesteric liquid crystal laser can be further improved, And the multiple of the increase is reduced with the increase of the thickness of the dye-doped cholesteric liquid crystal. The reason of this phenomenon and its physical mechanism are analyzed in this paper. It is worth mentioning that, by rubbing and adding the mirror, we have achieved the highest laser efficiency of up to 10% in a 10. m u.m laser sample, which is the highest laser efficiency so far in the cholesteric liquid crystal.
【学位授予单位】：浙江师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN248

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