减反膜的梯度化与激光损伤阈值之间的关系研究

光学减反膜是激光系统的重要组成部分，也是在激光照射下最容易发生损伤的部分，如何提高减反膜的激光损伤阈值是研究的热点之一。在保持目标透射光谱要求和膜系总光学厚度不变的前提下，研究了不同梯度化减反膜与激光损伤阈值之间的关系。首先采用混合渐变膜系设计方法设计了一种渐变减反膜系，G/H₁→H/L/A；其次通过渐变折射率分层等效方法将渐变减反膜系进行不同的梯度化，并利用PECVD技术，在K9玻璃上沉积了满足光学性能指标要求的不同渐变减反膜系(多层梯度渐变膜系和相应的坡度渐变膜系)；最后进行了激光损伤阈值(LIDT)测量。研究结果表明:在保持目标透射光谱要求和膜系总光学厚度不变的前提下，渐变减反膜系相比于传统减反膜系，抗激光损伤阈值有明显的提高；随着梯度化层数的增加，渐变减反膜系的激光损伤阈值呈减小的趋势；对于相同膜层的渐变折射率薄膜，采用坡度法制备的样片抗激光损伤阈值均优于采用梯度化制备的样片。     

双波段宽带减反膜的研究

根据电视/红外双色制导的要求,研制了锗酸盐基底上的双波段宽带减反膜。其膜系设计采用二氧化钛和二氧化硅分别作为高、低折射率膜料的13层膜堆,镀制的膜层满足环境稳定性标准。在0.56~0.75μm波长范围内,双面镀膜后的平均透过率大于98%,单面平均剩余反射率不超过0.5%;在3.6~4.8μm波长范围内,双面镀膜后的平均透过率至少可达到85%,单面平均剩余反射率不超过1.5%。     

基于时间控厚离子束溅射技术的宽带减反膜制备

 为了制备满足设计要求的宽角度、宽波段减反膜,利用离子束溅射沉积技术,在时间-功率控厚的模式下,对膜层沉积速率进行了精确修正。在实验中,利用时间-功率控厚的离子束溅射沉积技术,选择HfO₂和SiO₂作为高低折射率组合,在超抛ZF6玻璃基底上制备了宽角度、宽带减反膜,通过对实验后的透过率光谱曲线的数值反演计算,获得膜层厚度修正系数,初步得到了沉积速率随沉积时间变化的规律。利用修正后的沉积参数制备设计的膜系,在0°~30°入射角度下,600~1 200 nm波段的平均透过率达到99%以上。     

应用于投影显示系统的偏振分光镜的设计和制备

讨论了应用于投影显示系统的满足宽光谱范围、大的入射角、高的消光比的偏振分光镜的设计和制备。提出了一种偏振分光镜的新的设计方法 :采用多对迈克尼尔对组合来满足宽入射角范围的要求 ,采用多个中心波长不同的λ 4膜堆来满足宽光谱范围。设计的偏振分光镜在 42 0nm～ 6 70nm的波段范围内 ,在 41.34°～ 48.6 6°的入射角范围内 ,达到p偏振光的平均透过率大于 85 % ,p偏振光的平均透过率与s光的平均透过率之比大于 10 0 0。并给出了设计实例和样品的实测结果     

抗紫外辐射塑料显示面板的减反射膜

设计制备了一种抗紫外(UV)辐射的塑料显示面板的减反射膜.对常用的聚碳酸酯(PC)塑料面板,在垂直入射时,减反膜紫外波段300~380 nm的平均反射率大于99.5%,可见光波段420~750 nm的残余反射率为0.22%;在45°入射时,紫外波段300~360 nm的平均反射率大于98.8%,可见光波段400~700...     

离子束辅助淀积低温微光学元件红外宽带增透膜

简要叙述了锗基片微光学元件红外宽带减反膜的设计与制作。着重介绍了离子束辅助淀积制备该膜系的过程，给出了用该方法制作８～１２μｍ波段的减反膜的测试曲线，它具有峰值透过率高，在设计波长范围内的平均透过率大于９７％以上，膜层附着好，可以切割和擦洗，可以在室温和１００Ｋ低温下反复循环使用。     

渐变折射率减反膜的设计及其全向性能

相比于传统的多层减反膜,渐变折射率减反膜有更好的减反性能。通过沉积折射率介于基底与空气且均匀变化的介质材料可以制备渐变折射率减反膜。选择的制备方法不同,会导致渐变折射率减反膜的结构不同,其减反效果也有所差异。通过数值模拟仿真,研究不同结构的渐变折射率减反膜在不同入射角时的减反效果,可得出渐变折射率减反膜的最优结构。最优结构的渐变折射率减反膜当入射角为0°~45°时对可见光的反射率在0.6%以下,当入射角为75°时反射率低于15.5%。     

近红外宽截止窄带滤光膜的研制

在空间光通信系统中,为满足光学系统对滤光膜的特殊要求,研制出了一种近红外宽截止窄带滤光膜,实现了降低深背景范围内杂散光干扰的要求.通过对薄膜材料特性的研究、膜系设计曲线的不断优化,得到了相对易于制备的窄带滤光膜结构;采用电子束加热蒸发及离子辅助沉积技术制备薄膜,采用光控加晶控同时监控的方法监控膜层厚度,通过不断优化工艺参量,提高中心波长处的透过率,最终成功得到了光谱性能较好的滤光膜.经光谱测试表明:所镀膜层在800~1 530nm、1 600~1 800nm波段平均透过率低于0.3%,1 565nm单点透过率高于92%,通带半带宽为18nm,满足光学系统的使用要求.     

基于氧化物的0.8~1.7μm和3.7~4.8μm硬质宽带红外增透膜研制

从实际应用出发,在0°入射的条件下,在ZnS基底上针对0.8~1.7 μm和3.7~4.8 μm两个红外波段,设计并制备了双波段红外增透膜。论述了材料选择、膜系设计和制备方法,最终使用等离子辅助沉积技术在ZnS窗口上制备出双波段红外增透膜,透过率及环境测试结果表明：在0.8~1.7 μm波段双面平均透过率大于95%,在3.7~4.8 μm波段双面平均透过率大于96%。膜层结合牢固并有良好的耐摩擦性能。     

离子束溅射制备低应力深紫外光学薄膜

采用离子束溅射制备了Al F3、Gd F3单层膜及193 nm减反和高反膜系,分别使用分光光度计、原子力显微镜和应力仪研究了薄膜的光学特性、微观结构以及残余应力。在优选的沉积参数下制备出消光系数分别为1.1×10~(-4)和3.0×10~(-4)的低损耗AlF_3和GdF_3薄膜,对应的折射率分别为1.43和1.67,193 nm减反膜系的透过率为99.6%,剩余反射几乎为零,而高反膜系的反射率为99.2%,透过率为0.1%。应力测量结果表明,AlF_3薄膜表现为张应力而GdF_3薄膜具有压应力,与沉积条件相关的低生长应力是AlF_3和GdF_3薄膜残余应力较小的主要原因,采用这两种材料制备的减反及高反膜系应力均低于50 MPa。针对平面和曲率半径为240 mm的凸面元件,通过设计修正挡板,250 mm口径膜厚均匀性均优于97%。为亚纳米精度的平面元件镀制193 nm减反膜系,镀膜后RMS由0.177 nm变为0.219 nm。     

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.