激光安全与防护

TN241 2005010167 基于一维光子晶体带隙反射的YAG激光防护镜=Eye-protection glasses against YAG laser disservice based on the bandgap reflection of one-dimensional photonic crystal [刊,中]／陈明(中科院长春光机所激发态物理重点实验室．吉林,长春(130033)),马少杰…∥发光学报．-2004, 25(3)．-325-328 设计并制备了一种以磷酸盐玻璃为衬底的一维光子晶体YAG激光防护镜。其中一维光子晶体的带隙反射 1．06μm波长的光(透射率低达10-7),加上磷酸盐玻璃对     

15W光子晶体光纤激光器的研究

利用光子晶体光纤在原来输出功率3 4W的基础上,研制成功了激光输出15W的光子晶体光纤激光器,实验装置为典型的F P腔结构,分别采用二色镜和光纤端面作为高反射腔镜和激光输出腔镜 一端二色镜紧贴光纤的入射端面,它对1 0 5 μm～1 1μm波段信号光的反射率大于99% ,对976nm泵浦光透射率为93% ;另一端利用光纤端面4 %Fresnel反射作为输出端反馈与二相色镜构成了线形谐振腔 实验采用掺Yb3+ 双包层光子晶体光纤,长度为2 0m 内包层为2 0 0 μm ,外包层为380 μm ,Yb2 O3浓度为1 5mol % 当泵浦功率为6 0W时,获得了15W 1 1μm的激光输出 15W光…     

应用于量子通信中的1．55μm波段光孤子脉冲源的研制

在连续变量的量子通信中，光孤子压缩纠缠态是一种重要的传输载体，大功率飞秒脉冲的产生是整个工作的基础。本文介绍了作为光孤子源的Cr^4＋：YAG飞秒脉冲激光器的研制。我们采用Z形折迭腔，通过光学ABCD矩阵分析法，得出了谐振腔稳定工作的最优化光路参数。应用1．06μm波段的Nd：YAG激光器作为泵浦源，以布儒斯特角切割的Cr^4＋：YAG晶体作为激光工作物质，以半导体可饱和吸收镜（SBR）作为锁模元件，     

近中红外与1.06μm和1.54μm激光兼容隐身光子晶体研究

为实现飞行器高温部分的红外与激光兼容伪装,设计了一种基于一维光子晶体的近中红外与1.06μm和1.54μm激光兼容隐身材料。基于薄膜的传输矩阵法和异质结构理论,拓展了光子晶体的禁带宽度,使之覆盖近中红外波段;随后,利用掺杂原理,在光子晶体周期结构中引入了两种缺陷。结果显示,在1~5μm的带隙中出现了波长分别为1.06μm和1.54μm的缺陷模,反射率分别为1.21%和1.79%,这种具有"光谱挖空"特性的光子晶体可以实现近中红外与1.06μm和1.54μm激光兼容隐身。     

飞秒激光在掺Yb~(3+)磷酸盐玻璃中写入光波导及波导激光器的实验研究

利用重复频率为1kHz,中心波长为800nm,脉冲宽度为120fs的飞秒激光在掺Yb3+磷酸盐玻璃中刻写光波导,测试了不同参数下刻写的波导的导光模式,研究了写入速度和写入脉冲能量对模场直径、波导折射率的影响,给出了波导形成的写入窗口范围,对比测试了激光作用区域和未作用区域的荧光光谱特性。实验结果表明,在采用20×显微物镜,写入速度为20μm/s,写入脉冲能量为1.8μJ时,所得到的光波导在976nm波段模场直径为20μm,波导区域折射率改变为2.7×10-4,飞秒激光作用区域的荧光光谱与基质的荧光光谱几乎完全重合,荧光特性在飞秒激光作用后保持良好。利用双色镜和2%的输出耦合镜构成了法布里-珀罗(F-P)腔掺Yb3+波导激光器,获得了波长为1031nm的连续激光输出,激光功率为2.9mW。     

大功率LD抽运的Cr^4＋：YAG被动调Q Nd：YVO4激光器

在LD端面抽运的Nd：YVO4激光器中插入Cr^4＋：YAG晶体,获得了稳定的1．06μm波长的高重复率被动调Q脉冲激光输出。实验研究了抽运功率、腔长、输出镜透过率对输出功率的影响,以及不同抽运功率下脉冲重复频率和脉冲宽度的变化,并对结果进行了理论分析。当腔长为8cm,抽运功率为27W时,得到重复率37．8kHz、平均功率3．5W的调Q脉冲序列;单个脉冲能量为93μJ、脉宽为24ns、峰值功率为3．9kW。     

紫外区全角度光子晶体反射镜

根据角域叠加原理,在石英玻璃基板上用全介质膜系实现了紫外区域全角度一维光子晶体反射镜的设计。采用两个不存在全角度反射带的一维光子晶体在角域上叠加,通过传输矩阵方法,从理论上计算合成光子存在全角度禁带,禁带波长范围328．95～352．11nm,相对带宽为6．80％。实验上采用HfO2和SiO2两种薄膜材料,用电子束蒸发的方法在石英玻璃基板上制备合成光子晶体。若透射率在1％以下为光子晶体禁带,则禁带波长范围从331．2～350．4nm,相对带宽5．63％。从而证明了角域叠加设计的正确性。     

用Cr^4＋：YAG晶体实现Nd^3＋：YAG0.946pμm激光被动调Q运转

以Cr4^ :YAG晶体作为可饱和吸收体，氙灯作为抽运源，实现了Cr4^ :YAG晶体在0．946μm波长处的调Q运转。激光脉冲宽度为38ns，能量为1．7mJ。     

超短脉冲激光在掺Er3+ 磷酸盐玻璃中制备光波导的实验研究

超短脉冲激光通过非线性吸收调制光学材料折射率提供了一种高效制备集成三维光子器件的途径.掺Er³⁺磷酸盐玻璃由于其优异的特性以及在1.55μm通信波段附近的发射光谱,成为了集成光学主动增益材料中的研究热点.实验采用重复频率1 kHz,中心波长800 nm,脉冲宽度120 fs的钛宝石飞秒激光放大系统作为制备波导的光源,系统研究了加工参数对激光写入形貌、波导形成及光学特性的影响.实验结果表明,在狭缝整形辅助短焦物镜横向刻写条件下,写入脉冲能量为1.8μJ时,光波导可以在写入速度为10μm/s-160μm的较宽范围内形成;写入速度为40μm/s时,光波导写入脉冲能量参数窗口为1.6μJ-2.0μJ;波导写入深度在125μm-200μm范围时,波导横截面对称性较好且折射率修改明显;近场强度测量结果显示所制备波导近场强度分布对称,导光特性良好.通过有限差分法反推波导区域折射率修改分布,结果显示最大折射率修改为Δn=6.6×10^-4.截断传输损耗测量结果显示所制备波导的传输损耗低至0.91 dB/cm.     

实现全反射镜功能的光子晶体禁带特性

用传输矩阵法研究一维光子晶体G(AB)mC(AB)mH的能带特性及电场分布,结果发现:随着m的增大,在830—883nm波长范围内,光子晶体G(AB)mC(AB)mH禁带中的导带透射率逐渐趋于零,即光被禁止通过,实现全反射镜功能,且随着入射角的增大,光子晶体的禁带逐渐向短波方向移动。随着介质层G、H的折射率增大,光子晶体在833.6—879.1nm波长范围内出现大的禁带,亦实现全反射镜功能。光子晶体G(AB)5C(AB)5H内部存在很强的局域电场,即在光子晶体内传输的光,被强烈局域在禁带范围内,并在缺陷层C处达到极大值,而且随着m的增大,局域强度增强。这些光学传输特性,为研究、设计新型光学器件全反射镜、滤波器等提供指导。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.     

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.