Studies on the Technology and Mechanism of Laser Photoinduced Alignment of Liquid Crystal

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Different Approaches of Employing Cholesteric Liquid Crystals in Dye Lasers

Two ways of employing cholesteric liquid crystals in tunable dye lasers are considered: the cholesterics as distributed feedback medium and the cholesterics as resonator mirrors. In the dye doped distributed feedback cholesteric liquid crystal lasers the frequency tuning is achieved exploiting light induced effects or using a specially designed cell assembling a chiral dopant concentration gradient in combination with suitable distribution of different dyes. Another approach represents the lasing in a multilayer system consisting of a dye doped isotropic solvent sandwiched between two CLC layers.

Temperature-tunable lasing in negative dielectric chiral nematic liquid crystal

In this work, negative dielectric nematic liquid crystal SLC 12V620-400, chiral dopant S811, and laser dye DCM are used to prepare dye-doped chiral nematic liquid crystal laser sample. In order to investigate temperature-tunable lasing in negative dielectric chiral nematic liquid crystal, we measure the transmission and lasing spectrum of this sample. The photonic band gap （PBG） is observed to red shift with its width reducing from 71.2 nm to 40.2 nm, and its short-wavelength band edge moves 55.3 nm while the long-wavelength band edge only moves 24.9 nm. The wavelength of output laser is found to red shift from 614.4 nm at 20 ~C to 662.8 nm at 67 ~C, which is very different from the previous experimental phenomena. The refractive indices, parallel and perpendicular to the director in chiral nematic liquid crystal have different dependencies on temperature. The experiment shows that the pitch of this chiral nematic liquid crystal increases with the increase of temperature. The decrease in the PBG width, different shifts of band edges, and the red shift of laser wavelength are the results of refractive indices change and pitch thermal elongation.

Random lasing from dye-doped negative liquid crystals using ZnO nanoparticles as tunable scatters

This work demonstrates the realization of a lasing in scattering media,which contains dispersive solution of Zn O nanoparticles（NPs） and laser dye 4-dicyanomethylene-2-methyle-6-（p-dimethylaminostyryl）-4H-pyran（DCM） in negative liquid crystals（LCs） that was injected into a cell.The lasing intensity of the dye-doped negative LC laser can be tuned from low to high if the NPs concentration is increased.The tunability of the laser is attributable to the clusters-sensitive feature in effective refractive index of the negative LCs.Such a tunable negative liquid crystal laser can be used in the fabrication of new optical sources,optical communication,and liquid crystal laser displays.

Configuration optimization of laser guide stars and wavefront correctors for multi-conjugation adaptive optics

Multi-conjugation adaptive optics（MCAOs） have been investigated and used in the large aperture optical telescopes for high-resolution imaging with large field of view（FOV）.The atmospheric tomographic phase reconstruction and projection of three-dimensional turbulence volume onto wavefront correctors,such as deformable mirrors（DMs） or liquid crystal wavefront correctors（LCWCs）,is a very important step in the data processing of an MCAO＇s controller.In this paper,a method according to the wavefront reconstruction performance of MCAO is presented to evaluate the optimized configuration of multi laser guide stars（LGSs） and the reasonable conjugation heights of LCWCs.Analytical formulations are derived for the different configurations and are used to generate optimized parameters for MCAO.Several examples are given to demonstrate our LGSs configuration optimization method.Compared with traditional methods,our method has minimum wavefront tomographic error,which will be helpful to get higher imaging resolution at large FOV in MCAO.

A high precision phase reconstruction algorithm for multi-laser guide stars adaptive optics

Adaptive optics（AO） systems are widespread and considered as an essential part of any large aperture telescope for obtaining a high resolution imaging at present.To enlarge the imaging field of view（FOV）,multi-laser guide stars（LGSs） are currently being investigated and used for the large aperture optical telescopes.LGS measurement is necessary and pivotal to obtain the cumulative phase distortion along a target in the multi-LGSs AO system.We propose a high precision phase reconstruction algorithm to estimate the phase for a target with an uncertain turbulence profile based on the interpolation.By comparing with the conventional average method,the proposed method reduces the root mean square（RMS） error from 130 nm to 85 nm with a 30% reduction for narrow FOV.We confirm that such phase reconstruction algorithm is validated for both narrow field AO and wide field AO.

Fourier hologram method using Gerchberg-Saxton algorithm for parallel femtosecond laser processing

In order to improve femtosecond laser throughput,a parallel processing system consisting of liquid crystal on silicon(LCOS)device as spatial light modulator is put forward.A method is described for displaying Fourier hologram on LCOS,and a high uniformity of several diffraction peaks in the computer reconstruction is achieved.Application of this method to the parallel femtosecond laser processing is also demonstrated,and two intersecting rings and three tangent rings are fabricated respectively by one time in the photoresist.

Flat-Panel Laser Displays Based on Liquid Crystal Microlaser Arrays

Laser displays,benefiting from the characteristic merits of lasers,have led to the revolution of next-generation display technologies owing to their superior color expression.However,the acquisition of pixelated laser arrays as self-emissive panels for flat-panel laser displays remains challenging.Liquid crystal(LC)materials with excellent processability and optoelectronic properties offer considerable potential for the construction of highly ordered multicolor laser arrays.Here,we demonstrate flat-panel laser displays on LC microlaser pixel arrays through a microtemplate-assisted inkjet printing method.Individual organic red-green-blue(RGB)microlaser pixel arrays were obtained by doping dyes into LCs with photonic band edges to obtain single-mode RGB lasing,leading to a much broader color gamut,compared with the standard RGB color space.Then we acquired periodically patterned RGB pixel matrices by positioning LC microlasers precisely into highly ordered arrays,according to the well-organized geometry of the microtemplates.Subsequently,we demonstrated full-color flat-panel laser displays using the LC microlaser pixel matrices as self-emissive panels.These results provide valuable enlightenment for the construction of next-generation flat-panel laser display devices.

飞秒激光赋能液晶光子学

液晶作为一种典型的软物质材料,具有独特的物理性质和可控的分子结构,已经成为柔性光电子器件、软凝聚态物理等领域的交叉研究前沿。飞秒激光的高峰值功率、短脉冲特性与灵活且高精度的双光子聚合加工技术,为设计、制造新型可调控的液晶光子学微结构,操纵其中液晶分子的线性、非线性响应提供了有效的实验方案。利用飞秒激光赋能液晶光子学不仅能推动软物质这一新兴学科的快速发展,同时也将为未来光学器件的开发带来新的机遇。本文综述了利用飞秒激光诱导液晶中的非线性效应、飞秒激光加工液晶弹性体和利用飞秒激光加工的微结构实现液晶分子的面外取向及在液晶光子学器件方面的诸多应用,并介绍近年来有关方向在实际应用领域的研究进展。

基于液晶偏振光栅的大口径激光光束扫描系统

非机械式激光光束扫描系统具有体积小、重量轻、易集成等优势,在激光雷达、激光武器和激光通信等领域具有较大的应用前景,其通光口径决定着设备的工作距离、扫描精度和目标摧毁能力。基于液晶偏振光栅设计了一种全电控制的大口径激光光束扫描系统。采用液晶偏振光栅和液晶空间光调制器的协同工作方式,实现光束的大角度连续扫描;设计了光束扫描系统,并重点分析了级联液晶偏振光栅组的控制策略,给出了具体控制方法。最后,进行了激光光束的初步扫描实验,实现了70 mm口径光束在−16.575°~16.575°的偏转。该研究结果为激光光束的非机械式扫描控制提供了技术支撑,并在大口径激光扫描系统应用方面进行了初步探索。

非机械指向空间激光通信接收系统设计与分析

采用非机械指向结构能够极大缩小空间激光通信系统尺寸与重量,由于现有器件性能局限,目前尚未见到成熟的非机械指向空间激光通信接收系统。提出基于正交液晶级联偏振光栅与四象限探测器的空间激光通信接收光学系统,利用了正交液晶级联偏振光栅体积小、口径大、偏转范围大,及四象限探测器接收角度范围大的优势,根据正交液晶级联偏振光栅与四象限探测器的理论与器件性能,设计了光学系统,分析了探测器噪声、背景噪声、系统噪声对于通信与入射角度测量的影响,计算了可实现的通信速率,给出了系统的最大响应角速度。

双液晶偏振光栅系统的倾斜误差特性分析

为了精确控制激光光束指向,本文基于双液晶偏振光栅系统的光束指向算法,分析了系统中因光栅倾斜产生的误差。首先,采用一种基于衍射光栅方程的光线追迹方法求解出射光束指向,引入了入射光束指向和光栅倾斜角,通过与仿真结果进行对比,验证了该方法的正确性和精度。其次,通过对光栅不同倾斜情况的分析,本文给出了不同倾斜情况下光栅姿态的表达式,并结合光线追迹法得到了相应的出射光束指向表达式,并进一步分析了光栅倾斜产生的调零误差和旋转误差。研究结果表明,在0°~0.3°光栅倾斜角范围内,调零误差分别在0.25 mrad和2 mrad以内,旋转误差分别在85 mrad和430 mrad左右。本文方法可实现对双液晶偏振光栅系统中出射光束指向和光栅倾斜误差的精确计算。

基于LC-OPA的空间激光通信技术进展

液晶相控阵既可以在空间激光通信技术建立多点间空间激光通信链路,又能代替压电偏摆镜的精瞄方式。阐述液晶相控阵应用趋势;通过对液晶相控阵中液晶分子电致双折射和多缝衍射光束偏转原理,提出替压电偏摆镜配合终端进行瞄准捕获跟踪的方案;以“一对二”空间激光通信终端为例,提出基于液晶相控阵多点间空间激光通信终端方案和链路工作模式,分析方案优势,并进行未来展望。

基于编码成像的激光能量调控方法研究

为了有效提升光电成像系统焦平面探测器在外界存在激光干扰条件下的环境适应性,同时不显著降低原成像系统成像性能,提出了一种基于编码成像的激光能量调控方法,构建了一套以液晶空间光调制器为核心器件的编码成像实验系统并对该系统的成像性能进行了测试,设计了一套基于编码成像的激光能量调控实验验证系统并开展了多参数条件下编码成像抗激光干扰实验研究。实验结果表明,基于编码成像的激光能量调控方法可在不显著降低成像质量前提下有效提升焦平面探测器的抗激光干扰性能。

High damage threshold liquid crystal binary mask for laser beam shaping

In order to improve the damage threshold and enlarge the aperture of a laser beam shaper, photolithographic patterning technology is adopted to design a new type of liquid crystal binary mask. The inherent conductive metal layer of commercial liquid crystal electro-optical spatial light modulators is replaced by azobenzene-based photoalignment layers patterned by noncontact photolithography. Using the azobenzene-based photoalignment layer, a liquid crystal binary mask for beam shaping is fabricated. In addition, the shaping ability, damage threshold, write/erase flexibility and stability of the liquid crystal binary mask are tested. Using a 1 Hz near-IR(1064 nm) laser, the multiple-shot nanosecond damage threshold of the liquid crystal mask is measured to be higher than 15 J/cm^2. The damage threshold of the azobenzenebased photoalignment layer is higher than 50 J/cm^2 under the same testing conditions.

大动态能量自适应蓝/绿激光探测方法

针对水下无线光通信链路中近距功率饱和与远距功率不足导致的光信号采集失效的难题,提出一种大动态能量自适应蓝/绿激光探测方法。该方法在水下无线光通信系统中加入由电控液晶光阀、可调增益光电倍增管及FPGA板卡组成的增益可控探测模块,该模块在链路功率和探测器增益两个维度对通信链路形成闭环调控,以保证光电倍增管始终工作在最优状态,从而实现水下远距离、高速、大动态范围无线光通信。

Reverse mode switching of the random laser emission in dye doped liquid crystals under homogeneous and inhomogeneous electric fields

We report the observation of electric field induced random lasing in a dye doped liquid crystal system. This was achieved by using a liquid crystal host with negative dielectric anisotropy doped with laser dye PM 597 in a 75 μm cell with a homeotropic alignment layer. In the absence of an applied field, only amplified spontaneous emission was observed since the liquid crystal orientation was uniform. However, application of a field resulted in a fieldinduced planar-like configuration with local nonuniformity in liquid crystal orientation. This led to random lasing in the energized state(voltage greater than a transition threshold). The onset of lasing occurs by application of either a spatially homogenous or a spatially inhomogeneous electric field across the liquid crystal. The characteristics of the emission spectra as a function of different(i) dye concentration and(ii) applied voltage were investigated using nanosecond pulsed laser excitation at 532 nm. The effects of using an inhomogeneous field were compared to the use of a homogenous field and reported. It is shown that the spatial configuration can be used to alter the emission spectra of the system. The work is used to suggest a new configuration, referred to here as"reverse mode," for liquid crystal-based random lasers. This new configuration may provide additional avenues for their use in commercial devices.

TFT-LCD及触摸屏玻璃基板激光断切现象研究

激光切割技术已经成为玻璃生产及加工领域中的一种成熟的工业加工技术,具备高精度、高速度、高质量、高效率的优点。断切现象是薄膜晶体管液晶显示器(ThinFilmTransistorLiquid CrystalDisplay,TFT-LCD)及触摸屏玻璃基板激光切割的质量问题之一。文章从设备接地、激光器出光功率稳定性、光路和软体系统信号对接4个方面分析短切现象产生的原因,并给出相应的处理方法,以期为常见激光切割质量问题的处理提供参考。

电场作用下染料掺杂手性向列相液晶器件激光辐射谱研究

研究了电场作用下染料掺杂手性向列相液晶器件激光辐射谱。设计了两种电极结构,分别对正性和负性液晶器件施加横向和纵向电场,采用532nm的Nd∶YAG脉冲固体激光器泵浦样品。对正性液晶器件施加电场,在630~660nm范围获得多波长的激光输出。对负性液晶激光器件施加电场,获得调谐范围为18.5nm的激光输出。由器件织构和光子禁带的变化,进行了深入的分析。正性液晶器件,在电场力矩与扭曲力矩相互竞争过程中,引起液晶的流动,光子禁带上下浮动,因此不仅在禁带边沿,禁带内也出现激光辐射。而负性液晶器件随着电场强度增大,液晶螺距收缩,禁带蓝移,输出激光波长从681.0nm蓝移到662.5nm,出射激光波长为光子禁带边沿处。负性液晶器件在电场作用下的稳定性较好。

液晶激光投影显示系统设计

激光显示技术与传统显示技术相比,具有色域大、颜色饱和度高以及功耗低等优点,已成为下一代显示领域的主要技术。利用激光投影技术和液晶显示技术的特点,设计了一种基于液晶空间光调制器的液晶激光投影显示系统。该系统使用波长为532 nm的激光作为投影光源,采用ARM微处理器对240×320分辨率的液晶空间光调制器进行控制,实现了图像以及文字的投影显示。通过激光束匀光和激光散斑均化,提高了投影显示图像的辐照均匀性,抑制了激光散斑对于投影显示图像的影响。实验结果表明:研究液晶激光投影显示系统对于激光投影技术具有重要的意义。