High pulse energy output from tunable solid-state dye laser based on MPMMA doped with PM567

Tunable solid-state dye laser sample based on modified polymethyl methacrylate (MPMMA) with methanol co-doped with pyrromethene 567 (PM567) and Coumarin 440 (C440) was prepared. Tunable dye laser output wavelength from 546 to 594 nm was obtained in an oscillator-amplifier configuration. With the input seed laser energy being about 1.5 mJ, the highest dye laser output energy reached 113.9 mJ, and the corresponding conversion slope efficiency was 51.39%. To the best of our knowledge, the tuning range and narrow linewidth dye output energy is the best under the same condition so far. The linewidth for the seed laser and amplified laser were measured with the result of less than 0.2 nm. With the amplified medium being pumped at a repetition rate of 10 Hz with a pulse energy as high as 120 mJ (the fluence was 0.42 J/cm²), the laser output energy dropped to half of its initial value after approximate 43000 pulses.     

宽波长范围窄线宽波长连续可调的光纤激光器

研制了一种宽波长范围窄线宽波长连续可调的光纤激光器,激光器基于环形腔结构,采用980nm的半导体激光器作为泵浦源,掺铒光纤作为增益介质,使用一段未泵浦的保偏掺铒光纤作为饱和吸收体压窄线宽。使用光纤法布里-珀罗滤波器作为选频器件,通过调节光纤其驱动电压实现光纤激光器的波长扫描。利用激光器的相干长度与干涉仪干涉条纹的关系动态测量激光器的光谱线宽,最终得到了扫描范围为1515.1～1588.6nm,线宽小于0.025nm的波长连续可调的光谱输出。     

用于铷蒸气激光泵浦的窄线宽阵列半导体激光器

在激光二极管LD泵浦铷蒸气激光器中,窄线宽半导体激光是实现铷蒸气激光高效率输出的关键技术之一。基于体布拉格光栅（VBG）外腔技术,实现了40 W功率0.14 nm线宽的780 nm激光输出。采用半导体制冷片（TEC）控制VBG温度,使得该激光器空气中波长可从779.35 nm调谐至780.10 nm,可用于铷蒸气激光的高效泵浦。     

用于铷蒸气激光泵浦的窄线宽阵列半导体激光器

在激光二极管LD泵浦铷蒸气激光器中,窄线宽半导体激光是实现铷蒸气激光高效率输出的关键技术之一。基于体布拉格光栅（VBG）外腔技术,实现了40 W功率0.14 nm线宽的780 nm激光输出。采用半导体制冷片（TEC）控制VBG温度,使得该激光器空气中波长可从779.35 nm调谐至780.10 nm,可用于铷蒸气激光的高效泵浦。     

Asymmetric dynamic phase holographic grating in nematic liquid crystal

A new scheme for recording a dynamic phase grating with an asymmetric profile in C60-doped homeotropically aligned nematic liquid crystal(NLC) was presented.An oblique incidence beam was used to record the thin asymmetric dynamic phase holographic grating.The diffraction efficiency we achieved is more than 40%,exceeding the theoretical limit for symmetric profile gratings.Both facts can be explained by assuming that a grating with an asymmetric saw-tooth profile is formed in the NLC.Finally,physical mechanism and mathematical model for characterizing the asymmetric phase holographic grating were presented,based on the photo-refractive-like(PR-like) effect.     

Tunable face-centered-cubic photonic crystal formed in holographic polymer dispersed liquid crystals

We report on the fabrication and electro-optic measurements of face-centered-cubic (fcc) lattices in holographic polymer dispersed liquid-crystal materials. Four linearly polarized coherent plane waves were interfered to generate a fcc optical lattice that was subsequently and indefinitely recorded as an arrayed pattern of nanometer-sized liquid-crystal droplets (approximately 50 nm) at lattice nodes within a polymer matrix. Observed transmission spectra and Kossel diffraction curves are consistent with fcc crystal structure. A completely reversible 2% wavelength shift of the (+/- 111) stop band was observed on application of an electric field.     

二极管泵浦无机液体激光器出光实验研究

 为探索新的高能激光体系,搭建了二极管泵浦的液体激光器。采用激光二极管作为泵浦光源,单侧泵浦掺钕离子的无机激光液体,进行了出光实验。通过测量输出光束的近场分布、脉冲波形和光谱,证实实现了激光输出,输出激光的波长为1 053 nm。输出的单脉冲激光能量达到47 mJ,光-光转换效率达到14%。其光-光转换效率高出闪光灯泵浦液体条件下2个数量级,说明该激光体系具有向高能激光体系发展的前景。     

简单MOPA结构窄线宽激光突破5 kW近单模输出

高功率窄线宽光纤激光器在非线性频率转换、光谱合成以及相干合成等领域有着重要的应用前景。本文基于自研的复合腔结构窄线宽振荡器作为种子,采用单级主振荡功率放大技术（MOPA）,实现了5 kW高效率的近单模窄谱激光输出。通过优化振荡器的时序特性和放大级结构,受激拉曼散射、光谱展宽和热致模式不稳定效应得到综合抑制。在最高功率时,信号光的3 dB和20 dB线宽分别为0.48 nm和2.1 nm,放大器的斜率效率约为86.1%,拉曼抑制比为28.3 dB,光束质量M2约1.35。本研究工作对于高功率窄线宽光纤激光的发展和研究具有重要的指导意义。     

飞秒抽运随机激光输出波形的可控性研究

本文基于随机激光的时域理论,研究了飞秒脉冲抽运下二维随机激光的辐射特性,并着重讨论了抽运脉冲的峰值强度、脉宽和脉冲波形对辐射光时域波形的影响.结果表明, 辐射光的时域波形强烈依赖于抽运光脉冲的参数,通过调整抽运方式可以控制辐射光的输出波形.数值模拟结果为研究随机激光输出波形的可控性技术提供了理论依据. 关键词： 激光物理 随机激光器 飞秒抽运 脉冲波形     

Optical pumping experiments using a cw dye laser with a narrow spectral output

An optical pumping experiment on the Na atoms of an atomic beam by means of a continuous wave dye laser is described. The atoms interact at two different regions with the laser beam. In the first region the atoms are optically pumped so that a Zeeman coherence in their substates is produced. In the second light beam the coherence is probed. Any changes in the phase of the eigenfunction of the atom through interaction in a magnetic field, or through collisions, or other effects occuring in the light free section can thus be sensitively detected. The possible applications of the set-up are discussed.     

窄线宽光纤激光器在1 030 nm波段实现3 kW近衍射极限输出

基于大模场面积掺镱光纤搭建了全光纤1 030 nm高功率窄线宽光纤激光主振荡功率放大系统,实现了3 004 W的最高功率输出,斜率效率69.27%,是目前报道的输出功率最高的1 030 nm波段近衍射极限光纤激光器。最高输出功率时,x,y方向的光束质量因子分别为1.169,1.174,3 dB光谱宽度为0.18 nm,放大自发辐射抑制比达到37 dB。     

Tunable lightwave propagation in two-dimensional hole-type photonic crystals infiltrated with nematic liquid crystal

Photonic crystals have many potential applications because of their ability to control lightwave propagation. We have investigated the tunability of lightwave propagation in two-dimensional hole-type photonic crystal structures. The linear waveguides can be obtained by the infiltration of liquid crystals into air holes in hole-type photonic crystal with square lattices. The refractive indices of liquid crystals can be changed by rotating the directors of liquid crystals. Therefore, we can control the lightwave propagation in two-dimensional hole-type photonic crystal structures. Such a mechanism of lightwave adjustment should open up a new application for designing components in photonic integrated circuits.     

Optical-induced Freedericksz transition of nematic liquid crystal doped with porphyrin (ZnTPP)

In this Letter, we studied the optical-induced Freedericksz transition of 5CB doped with 1% volume fraction of bio-molecule, porphyrinozinc(II) (ZnTPP). Excited by Ti:sappire laser with the 82 MHz repetition rate and 100 fs pulse duration, the optical Freedericksz threshold of a 23.6 μm-thickness planar alignment sample occurred at an intensity level of 0.35 mW/mm² in contrast to the normally observed 83 mW/mm² value for pure 5CB.     

Specific features of luminescence quenching in a nematic liquid crystal doped with nanoparticles

The change in the intensity of the photoluminescence (PL) spectra of nematic liquid crystal (NLC) composites as a function of the concentration of CdSe/ZnS semiconductor quantum dots (QDs) and TiO₂ and ZrO₂ nanoparticles ~5 nm in diameter has been investigated. It is shown that the PL-quenching intensity in composites with CdSe/ZnS QDs exceeds that in composites with TiO₂ and ZrO₂ nanoparticles. The lowfrequency spectra of these composites with a concentration of 0.1 wt %, recorded in the range of 10²–10³ Hz, and the content of mobile ions in them have been investigated. It is found that the dielectric loss in the composite with CdSe/ZnS QDs is much higher and the content of mobile ions is larger by a factor of 3 than in the composites with TiO₂ and ZrO₂ nanoparticles. It is shown that an increase in the CdSe/ZnS QD concentration in NLC composites leads to an increase in the dielectric loss and a decrease in the PL intensity. Possible mechanisms of the interaction between NLC molecules and CdSe/ZnS QDs are discussed.     

Improved dielectric and electro-optical parameters of nematic liquid crystal doped with magnetic nanoparticles

This study investigates the effect of magnetic nanoparticles(NPs) on the weakly polar nematic liquid crystal(NLC).Different parameters of dielectric data were measured for both the homeotropic and planar aligned samples as a function of frequency and temperature and the substantial changes have been noticed for the doped systems. Dielectric permittivity has been increased after the dispersion of magnetic NPs in the pure NLC. Dielectric anisotropy has also been influenced by incorporating the magnetic NPs with the NLC molecules. These results were attributed to the dipole–dipole interaction between the magnetic nanoparticles and nematic liquid crystal molecules. Electro-optical study indicated the faster rise time and fall time of the doped systems as compare to pure NLC. Threshold voltage has been calculated and found to be decreased for the doped systems. Moreover, we have also calculated the rotational viscosity and the splay elastic constant for pure and the doped systems. Both the rotational viscosity and splay elastic constant of the doped systems are found to be considerably lower than those of pure NLC. Change in these properties has been explained on the basis of molecular disturbances created by the interaction between the magnetic nanoparticle and LC director. This study reveals that the inclusion of magnetic NPs in weakly polar NLC can be useful to enhance the basic properties of the weakly polar NLC and make it a promising material for many display applications.     

Tunable optical vortex arrays using spontaneous periodic pattern formation in nematic liquid crystal cells

Controllable liquid crystal (LC) defects can provide an effective approach to creating tunable optical vortices. We develop a method to create tunable matter vortex arrays in an LC cell, in which +1 and −1 defects are periodically arranged in a square grid lattice. Spontaneous formation of the periodic defect array is achieved using a spontaneous standing pressure wave without using any patterned electrode or patterned alignment layer. The +1 and −1 defects in the array can induce optical vortices with opposite handedness, and the matter vortex array produces a periodic optical vortex array with orbital angular momenta of −2ℏ and +2ℏ in the same grid lattice. Because the pitch of the grid can be controlled, the method can provide a useful pathway to producing tunable optical vortex arrays for various applications such as advanced optical communication and quantum computation.     

基于增强瑞利反馈的单模窄线宽随机激光器

仿真说明了单模光纤(SMF)中瑞利散射(RS)的机理, 指出纤芯掺杂的不均匀性以及拉丝过程引起的光纤几何尺寸的随机变化是光纤中RS产生的主要原因, 并以此为基础制作了损耗为0.54 dB/km的散射光纤. 在通信波段, 5 km该散射光纤的瑞利背向散射(RBS)强度高于相同长度的SMF-28近5 dB. 在基于RBS单模随机激光器的数值模拟中, 大量的具有随机幅度和相位的纵模在经历不平坦增益的多次放大之后, 只有在增益最大点附近的模式能够克服损耗成为输出模式. 实验中以掺铒光纤作为增益介质, 500 m散射光纤提供随机反馈, 窄带布拉格光纤光栅(FBG)作为波长选择器件, 得到线宽约3.5 kHz、对比度近50 dB的单模激光输出. 与采用相同长度SMF-28的随机激光器相比, 其阈值电流降低了80 mA, 相同抽运条件下的最大输出功率提高了3 dBm. 该单模窄线宽随机激光器的输出波长的调谐特性仅由FBG的中心波长决定.     

Transmission type twisted nematic liquid crystal display for three gray-level phase-modulated holographic data storage systems

Gray-level data pages enhance the storage capacity of holographic data storage systems. A balanced three gray-scale data page in phase mode produces a homogenized Fourier spectrum which is regarded to be necessary for suitable exploitation of the holographic recording medium. A commercially available transmission type twisted nematic liquid crystal display has been characterized for use as a phase spatial light modulator with phase modulation in the range 0–3π/2 at 532 nm wavelength, such that it may be used for holographic data storage with binary as well as three gray-level phase-modulated data pages. Experimental results of the phase and amplitude modulation characteristics of the SLM, Fourier plane homogeneity, and recording of phase-modulated binary, three gray-level data pages and their reconstruction with a real-time holographic interferometric method are presented.