Theoretical study on the lasing plasmon of a split ring for label-free detection of single molecules and single nanoparticles

This paper reports the plasmonic lasing of a split ring filled with gain material in water. The lasing mode(1500 nm)is far from the pump mode(980 nm), which can depress the detection noise from the pump light. The laser intensities of the two modes simultaneously increase by more than 10~3 in amplitude, which can intensify the absorption efficiency of the pumping light and enhance the plasmonic lasing. The plasmonic lasing is a sensitive sensor. When a single protein nanoparticle(n = 1.5, r = 1.25 nm) is trapped in the gap of the split ring, the lasing spectrum moves by 0.031 nm, which is much larger than the detection limit of 10~(-5) nm. Moreover, the lasing intensity is also very sensitive to the trapped nanoparticle. It reduces to less than 1/600 when a protein nanoparticle(n = 1.5, r = 1.25 nm) is trapped in the gap.     

基于液晶/聚合物光栅的高转化效率有机半导体激光器

采用有机半导体发光材料聚[2-甲氧基-5-(2-乙基己氧基)-1,4-苯乙炔]作为增益介质,低官能度光敏单体制备的液晶/聚合物光栅作为外部反馈谐振腔,制备出参数可独立控制的分离式结构的有机半导体激光器.液晶/聚合物光栅中液晶分子的取向影响光栅折射率调制量,从而影响光栅的反馈能力,最终影响激光器出射激光的性能.通过研究发现决定液晶分子取向的主要有两种与光栅周期有关的作用力,利用这一原理制备不同周期的光栅,光栅周期小于450 nm时,相分离出的液晶分子取向由光栅矢量方向变为光栅沟槽方向,此时光栅的折射率调制量增加,光反馈能力增强.采用周期为395 nm的液晶/聚合物光栅制备二级布拉格散射的有机半导体激光器,相较于大周期光栅(593 nm)制备的激光器,激光阈值由0.70μJ/pulse降低至0.18μJ/pulse,转化效率由2.5%提高到6.4%,且出射激光垂直于基板表面发射,有利于后续的处理及应用.     

Wavelength-spacing tunable multi-wavelength fiber optical parametric oscillator based on multiple four-wave mixing

We propose a wavelength-spacing tunable multi-wavelength fiber optical parametric oscillator (MW-FOPO) with a simple line cavity and one pump source based on multiple four-wave mixing (MFWM). Stable multi-wavelength lasing at room temperature is achieved due to the four-wave mixing effect and the broadband gain of the fiber optical parametric amplifier based on a highly nonlinear fiber. The wavelength spacing of the proposed MW-FOPO can be tuned by adjusting the wavelength of the pump light or the central wavelength of the fiber Bragg grating. Seventeen lasing lines with a wavelength spacing of 2.89 nm and an extinction ratio larger than 10 dB, which covers the wavelength region from 1540 to 1568 nm is demonstrated.     

Random lasing from dye-doped chiral nematic liquid crystals in oriented and non-oriented cells

These are the experimental results describing random lasing in dye-doped chiral nematic liquid crystals. A novel random lasing emission is studied in this article based on the helical domains of dye-doped chiral nematic liquid crystals in oriented and non-oriented cells. Under frequency doubled 532 nm Nd:YAG (yttrium aluminum garnet) laser-pumped optical excitation, we carefully observed and analysed random lasing from dye-doped chiral nematic liquid crystals with wavelength ranges from 600 nm to 620 nm. In addition, the line-width of multi-mode peaks is less than 0.2 nm. The difference between the two random lasing behaviours in the oriented and non-oriented cells arises from the fact that random lasing appearing in the oriented cell results from stronger multiple scattering of light generated by the spiral domains of the liquid crystal molecules. Furthermore, chiral nematic liquid crystal micro-domains with different orientations can induce variation of the diffusion constant, thereby resulting in a decrease or increase in the lasing intensity of the random lasers, and an increase or decrease in their energy thresholds. In addition, a detailed comparison of the two experimental results is also presented in the article, showing the dependence of the lasing threshold and the number of lasing modes on the transport mean free path, the excited area, and the sample size. This process allows us to obtain a random laser by changing the structure of the sample, realising tunable random lasers at low cost.     

纳米ZnO粉末中随机激光现象

实验采用三倍频Nd:YAG(波长355 nm，脉宽8ns，频率30Hz) 脉冲激光器作为抽运光源，在ZnO纳米粉末(直径～100 nm)中发现了类似激光现象.并用环形腔理论模拟了ZnO的颗粒密度对平均自由程的影响，从理论上证明在纳秒级激光器的抽运下，ZnO纳米粉末也可以发射激光. 关键词： 类似激光 ZnO纳米粉末 平均自由程     

Bichromatic coherent random lasing from dye-doped polymer stabilized blue phase liquid crystals controlled by pump light polarization

In this paper, we investigate the bichromatic coherent random lasing actions from the dye-doped polymer stabilized blue phase liquid crystals. Two groups of lasing peaks, of which the full widith at half maximum is about 0.3 nm, are clearly observed. The shorter- and longer-wavelength modes are associated with the excitation of the single laser dye (DCM) monomers and dimers respectively. The experimental results show that the competition between the two groups of the lasing peaks can be controlled by varying the polarization of the pump light. When the polarization of the pump light is rotated from 0° to 90°, the intensity of the shorter-wavelength lasing peak group reduces while the intensity of the longer-wavelength lasing peak group increases. In addition, a red shift of the longer-wavelength modes is also observed and the physical mechanisms behind the red-shift phenomenon are discussed.     

Random lasing in dye-doped polymer dispersed liquid crystal film

A dye-doped polymer-dispersed liquid crystal film was designed and fabricated,and random lasing action was studied.A mixture of laser dye,nematic liquid crystal,chiral dopant,and PVA was used to prepare the dye-doped polymer-dispersed liquid crystal film by means of microcapsules.Scanning electron microscopy analysis showed that most liquid crystal droplets in the polymer matrix ranged from 30 μm to 40 μm,the size of the liquid crystal droplets was small.Under frequency doubled 532 nm Nd:YAG laser-pumped optical excitation,a plurality of discrete and sharp random laser radiation peaks could be measured in the range of 575–590 nm.The line-width of the lasing peak was 0.2 nm and the threshold of the random lasing was 9 m J.Under heating,the emission peaks of random lasing disappeared.By detecting the emission light spot energy distribution,the mechanism of radiation was found to be random lasing.The random lasing radiation mechanism was then analyzed and discussed.Experimental results indicated that the size of the liquid crystal droplets is the decisive factor that influences the lasing mechanism.The surface anchor role can be ignored when the size of the liquid crystal droplets in the polymer matrix is small,which is beneficial to form multiple scattering.The transmission path of photons is similar to that in a ring cavity,providing feedback to obtain random lasing output.     

Dramatic enhancement of optical-field-ionization collisional-excitation x-ray lasing by an optically preformed plasma waveguide

Dramatic enhancement of optical-field-ionization collisional-excitation x-ray lasing is achieved by using an optically preformed plasma waveguide. With a 9-mm-long pure krypton plasma waveguide prepared by using the axicon-ignitor-heater scheme, lasing at 32.8 nm is enhanced by 400 folds relative to the case without the plasma waveguide. An output level of 8 x 10(10) photon/shot is reached at an energy conversion efficiency of 2 x 10(-6). The same method is used to achieve x-ray lasing in a gas jet for the high-threshold low-gain transition at 46.9 nm in neonlike argon.     

Efficient high-power UV laser generated by an optimized flat–flat actively Q-switched laser with extra-cavity harmonic generations

We investigate the parasitic lasing effect in the high-power actively Q-switched laser with a flat–flat resonator. The parasitic lasing effect in the low-Q stage is found to lead to long tails in the output pulses, corresponding to the peak-power reduction. We experimentally determine the shortest cavity length without the parasitic lasing effect to optimize the performance of the high-power actively Q-switched laser with a flat–flat cavity. We further use the optimized fundamental laser to generate green and UV lasers by extra-cavity harmonic generations. At a pump power of 44 W, the output powers at 355 nm and 532 nm as high as 6.65 W and 8.38 W are obtained at a pulse repetition rate of 40 kHz.     

基于全息液晶/聚合物光栅的分布反馈式激光器的波长调谐特性研究

首先制备了不同周期的染料掺杂全息液晶/聚合物光栅并进行激光抽运实验, 得到了激光器的调谐曲线,确定了激光器在574 nm到685 nm的谱带里均可以实现激光输出, 即激光器具有110 nm左右的可调谐范围. 之后, 通过温控仪控制样品的温度, 对周期为610 nm的染料掺杂全息液晶/聚合物光栅进行激光抽运, 探测不同温度下的输出激光光谱, 观察到随着温度由20℃升高到65℃, 激光器的中心波长由627.9 nm减小到623 nm, 产生了4.9 nm的波长蓝移.     

New biochemical material laser emission in microdroplets using ribo-flavin and its enhancement by mixing highly scattering intralipid medium

New laser emission from a biochemical material, ribo-flavin (vitamin B₂), at 570 nm was observed for the first time in liquid microdroplets pumped at 475 nm using a pulsed optical parametric oscillator. Laser emission spectra from microdroplets containing ribo-flavin in water and glycerol solution exhibit periodic mode structures depending on the microdroplet diameter demonstrating the morphology-dependent resonances. Magnitude enhancement of lasing emission is confirmed experimentally from liquid microdroplets of ribo-flavin solution with appropriate mixture of the fat emulsion Intralipid-10% suspension as highly scattering medium. We believe that such biochemical-soft multiple light scatterer systems may allow a wide range lasing of other bio-materials and even lead to the discovery of some novel species as well as highly sensitive analysis and diagnosis for future applications.     

A multiwave CuBr and PbBr2 laser with a sectioned active volume

The operation of a CuBr and PbBr₂ laser with a two-section gas-discharge tube with working media in different sections and an additional electrode between the sections was studied for the first time. Effective lasing was achieved in both media under control of time location of lasing pulses in different active media. The total mean lasing power equal to 1.5 W was distributed over wavelengths as follows: 1 W (510.6 nm), 0.3 W (578.2 nm), and 0.2 W (722.9 nm). The specific features of operation of the multicomponent laser and methods for its optimization are discussed. It is shown that the lasing power in a section is close to the power of an individual active element.     

Studies on the SFD Properties of Nd_xGd_(1-x)Ca_4O(BO_3)_3 Solid-solution Crystal

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｉｎｔｈｅｐａｓｔｆｅｗｙｅａｒｓ,ｓｍａｌｌｓｉｚｅｄＳＦＤｌａｓｅｒｈａｓａｔｔｒａｃｔｅｄｇｒｅａｔａｔｔｅｎｔｉｏｎｓ.Ｌａｓｅｒｄｉｏｄｅ(ＬＤ)ｐｕｍｐｅｄｓｏｌｉｄｓｔａｔｅｌａｓｅｒｓｈａｖｅｂｅｅｎｆｏｕｎｄｖｅｒｙｕｓｅｆｕｌｉｎｔｈｅｆｉｅｌｄｓｏｆｍｉｌｉｔａｒｙ,ｉｎｄｕｓｔｒｙ,ｍｅｄｉｃａｌｔｒｅａｔｍｅｎｔａｎｄｓｃｉｅｎｔｉｆｉｃｒｅｓｅａｒｃｈｅｓｄｕｅｔｏｔｈｅａｄｖａｎｔａｇｅｓｏｆｈｉｇｈｓｔａｂｉｌｉｔｙ,ｃｏｍｐａｃｔｎｅｓｓ…     

梳状电极胆甾相液晶激光器的激光辐射谱

设计制作了梳状电极染料掺杂胆甾相液晶激光器件,研究了外加电压下的激光辐射谱。器件的下基板ITO电极刻蚀成梳状条形电极,电极宽度约2 mm,相邻电极间距分别约为1,3,5 mm。上基板无ITO电极。上下基板取向膜平行摩擦取向处理,使胆甾相液晶平面态排列。以532 nm的Nd∶YAG激光器作为泵浦光源,测量器件激光辐射谱。改变外加电压0~100 V,3个区域均出现了多模输出。在1 mm电极间距区域,可获得633.65~621.52 nm（12 nm）和683.15~664.35 nm（18 nm）的可调谐波长范围;在电极间距3,5 mm区域,辐射激光波长变化微小。在外加电压作用下,液晶分子均匀的螺旋周期排列受到扰动,液晶分子层螺旋轴倾斜,各个液晶畴的螺旋轴取向不一致,使有效螺距值缩短并有所浮动,引起出射激光波长蓝移和多模输出。利用光子态密度理论数值模拟了激光辐射谱。当有效螺距为倾斜角的函数时,随着倾斜角增大出射激光波长蓝移。     

Studies on the SFD Properties of NdxGd1-xCa4O(BO3)3 Solid-solution Crystal

NdxGd1-xCa4O(BO3)3 (NdGdCOB) is a new self-frequency-doubling (SFD) solid-solution crystal. The second-harmonic generation (SHG) phase-matching (PM) curves were calculated by using refractive indices. The deff of NdGdCOB crystal along different PM directions were calculated according to the sellmeier equation and dijk data in which the (θ=66.8°, φ=132.6°) PM direction has the highest deff. SFD experiments were carried out with Ti:sapphire CW laser and pulsed dye-laser. A green laser output power up to 225 mW at 530 nm was achieved from a 7×3×3 mm3 crystal sample pumped by 1560 mW CW Ti:sapphire laser. The lasing threshold of SFD was lower than 1.8 mW along the PM direction (66.8°,132.6°). The optical-optical conversion efficiency was 14.4%. The conversion efficiency was 7.7% when 10×3×3 mm3 sample was side-pumped by the pulsed dye-laser tuned to 595.4 nm with 17.5 mJ energy and the lasing threshold is 1.2 mJ.     

Synthesis, morphology and random laser action of ZnO nanostructures

Three-dimensional (3-D) ZnO random-wall nanostructures and one-dimensional (1-D) ZnO nanorods were prepared on silicon substrates by a simple solid-vapour phase thermal sublimation technique. Optical pumped random lasing has been observed in the ZnO random-wall arrays with a threshold intensity of 0.38 MW/cm² in the emission wavelength from 380 to 395 nm. The optical gain was attributed to the closed-loop scattering and light amplification of the ZnO random-wall. The experimental result suggests that the morphology of nanostructure is the key factor to effect random lasing.     

染料掺杂聚合物薄膜中金纳米颗粒增强的随机激光

基于金属纳米结构而获得随机激光的增强,其独特的性质及其潜在的应用价值具有重要的研究意义,在表面增强荧光、光学开关器件、表面等离子激元激光等方面实现了较多应用。报道一种快捷有效的制备纳米颗粒的手段并基于该纳米颗粒结构分析了染料掺杂聚合物薄膜涂覆的随机激光现象和规律。利用离子溅射沉积和高温热处理在石英基底上制备了Au纳米颗粒,改变溅射时间Au纳米颗粒的尺寸发生可控变化,该方法便捷、工艺简单。研究采用40,80和120 s三种不同的时间进行Au膜溅射并在650 ℃下高温处理,得到粒径尺寸不同的Au纳米颗粒,随着溅射时间延长Au纳米颗粒的尺寸逐渐变大。通过涂覆有机荧光染料DCJTB掺杂的PMMA聚合物薄膜构建光致激射系统,利用纳秒脉冲激光对样品进行激发,得到随机激光并研究其出射光强度和阈值的变化规律特征。40,80和120 s三种溅射时间下所得Au纳米颗粒的平均粒径尺寸分别为230,250和390 nm,在532 nm激光激发下产生随机激光的阈值分别为20.5,17.5和12.5 μJ·pulse-1。Au纳米颗粒尺寸越大、粒子间距越小时,光子散射的平均自由程越短,光在金属颗粒之间可以多次有效散射,从而显著提高散射效率,产生较低阈值的激光发射;Au纳米颗粒的吸收峰与染料的荧光峰恰好匹配时,将会显著增强染料的荧光效应,激发更多染料分子发生能级跃迁,增加光子态密度,获得峰值更高、阈值更低的激射现象;泵浦光不破坏染料分子的情况下,可以多次循环泵浦获得激光,染料分子的发光效率随着多次激发略有降低,有助于随机激光器件的研究开发。实验研究结果与理论分析相一致,进一步明确了Au纳米颗粒对光子散射和等离子共振对光吸收增强的随机激光发射机理。该研究以Au纳米结构对光子的强散射效应为增益,通过理论分析和实验测量获得随机激光,为实现高效率、低阈值的随机激光研究提供了一种便捷的技术手段,有望促进随机激光器件的开发和应用。     

T-matrix approach to calculating circular polarization of aggregates made of optically active materials

Optical activity is a typical property of the biological materials where left-handed amino-acids and right-handed carbohydrates dominate (so called homochirality). Observationally, optically active materials reveal themselves through the circular polarization in the light they scatter. Thus, circular polarization produced by the optically active particles can serve as a biomarker. It is known that biological (e.g. colonies of bacteria) and pre-biological (e.g. dust in comets) particles often have a complex structure that can be modeled presenting them as aggregates of small monomers. This motivated the development of the T-matrix code presented in this paper, which enables calculation of the scattering matrix - including circular polarization - of the light scattered by aggregated optically active particles. The code can be used for modeling the light scattering by biological objects (e.g. colonies of bacteria, blood cells) and for interpretation of the circular polarization produced by the cosmic dust that contains (pre)biological organic, e.g. comet dust or planetary aerosols.     

Raman lasing near 650 nm from pure water microdroplets on a superhydrophobic surface

We demonstrate Raman lasing near 650 nm in pure water microdroplets located on a superhydrophobic surface. In the experiments, stationary, pure water microdroplets were prepared on a superhydrophobic surface and excited by a pulsed, frequency-doubled Nd:YAG laser at 532 nm. Intense laser emission was observed at frequencies corresponding to the whispering gallery mode resonances of the water microdroplets near 650 nm where Raman resonances due to OH-stretching bonds of water are located. On–off behavior was observed during lasing and the average temporal inter-burst separation was determined from the time-dependent intensity traces. Our results can find applications in the development of novel organic light emitters for short-haul communication systems, and in the spectroscopic characterization of water microdroplets on a surface.     

Large Signal Modulation Characteristics in the Transition Regime for Two-State Lasing Quantum Dot Lasers

Large-signal modulation capability,as an important performance indicator,is directly related to the high-speed optical communication technology involved.We experimentally and theoretically investigate the large-signal modulation characteristics of the simultaneous ground-state(GS) and the excited-state(ES) lasing in InAs/GaAs quantum dot laser diodes.The large-signal modulation capability of total light intensity in the transition regime from GS lasing to two-state lasing is unchanged as the bias-current increases.However,GS and ES large-signal eye diagrams show obvious variations during the transition.Relaxation oscillations and large-signal eye diagrams for GS,ES,and total light intensities are numerically simulated and analyzed in detail by using a rate-equation model.The findings show that a complementary relationship between the light intensities for GS and ES lasing exists in both the transition regime and the two-state lasing regime,leading to a much smaller overshooting power and a shorter settling time for the total light intensity.Therefore,the eye diagrams of GS or ES lasing are diffuse whereas those of total light intensity are constant as the bias-current increases in the transition regime.