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在驻波场理论基础上,用表面和界面强吸收理论模型,计算出了激光辐照下两种不同反射膜系中温度场的“多峰”分布特性,分析了激光对薄膜的热力损伤特性、主要破坏模式和阈值条件。结果表明,光学薄膜对激光能量的吸收,主要由驻波场分布及膜层的消光系数决定;膜系表面的杂质吸附层和界面吸收层是膜系的主要能量沉积区,从而在这些界面形成温度场的“多峰”分布,界面因此成为最容易受激光损伤的部分。导致光学薄膜激光损伤的主要模式为膜层熔融和脱落两种。如果膜层中含有杂质,则容易诱导杂质处膜层剥落破坏。 相似文献
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在多层介质薄膜中,激光的入射方式是影响薄膜抗损伤能力的关键因素之一.提出了一种模拟锥角高斯光入射多层介质薄膜后电场和热场分布的方法.该方法能够分析薄膜中高斯光各个角谱分量叠加形成的电场分布,进而得到由于薄膜本征吸收产生的热量沉积以及薄膜内部的温度场分布.针对中心波长为4.3 μm的中红外高反膜进行了分析,给出了高反膜系的温升峰值随激光入射角度和偏振态的变化.结果表明:对于s偏振光,斜入射时膜系的最高温升峰值高于垂直入射峰值,而p光的结果则相反.此种模拟方法克服了原有方法对激光入射角度的限制,较好地反映出斜入射情况下激光偏振态对薄膜损伤的影响.
关键词:
多层介质薄膜
高斯光
热过程
数值分析 相似文献
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介绍了由滤光片膜层结构决定的激光在光学薄膜中形成温度场及驻波场特性。用1.06μm调Q Nd:YAG激光器,在激光脉冲宽度10ns和光斑直径0.61μm的条件下,进行了激光辐照红外滤光片的损伤特性实验研究。根据脉冲激光辐照红外滤光片后样品损伤分析,发现滤光片的最初损伤发生在里面的膜层中,从而在实验上验证了计算得到的滤光片膜层中存在其温度场及驻波场的结果。它对提高红外滤光片的抗激光辐照能力研究具有一定的参考价值。 相似文献
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提出一种全面分析光学薄膜损伤特性的方法,根据热传导理论与电子增殖理论建立激光辐照下多层介质膜的损伤理论模型。以HfO2/SiO2多层高反膜为例,计算红外纳秒脉冲激光作用下膜系内部的温度场、应力场以及自由电子数密度分布,对其热学特性与电子增殖特性进行综合评估后,得到不同输入条件下膜系的损伤阈值。结果表明,薄膜材料的损伤特性会受到驻波场的影响,在1064 nm波长的激光辐照下HfO2/SiO2 多层介质薄膜的热致应力损伤效应先于热熔融效应先于场效应发生,且薄膜中SiO2层发生热损伤,而薄膜并未发生场损伤,此外薄膜的损伤阈值随着激光脉宽的增大而增大。 相似文献
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HfO_2/SiO_2高反膜、增透膜及偏振膜的1064nm激光损伤特性 总被引:2,自引:0,他引:2
高反膜、增透膜和偏振膜是Nd∶YAG激光器中的关键薄膜元件 ,其抗激光损伤能力直接影响到激光器的输出能量和功率。由于优异的物理化学性能 ,高功率Nd∶YAG激光器的光学薄膜一般采用HfO2 /SiO2 膜料组合镀制 ,因而用此膜料镀制的光学薄膜的激光损伤特性是薄膜工作者重点关注的问题。对光学中心APS15 0 4镀膜机镀制的HfO2 /SiO2 高反膜、增透膜和偏振膜等开展了 10 64nm的激光损伤实验研究 ,用 2 0 0倍的Normaski显微镜详细分析了高反 ,增透和偏振膜的激光损伤图貌 ,发现对于脉宽为 10ns波长的 10 64nm的激光而言 ,高反膜基本表现为孔洞和等离子体烧蚀疤痕 ,孔洞是由薄膜中的节瘤 (nodular)缺陷的激光损伤引起的 ,损伤的能流密度较低 ,为薄膜的零损伤阈值密度。疤痕为薄膜的激光等离子体烧伤引起的 ,尺寸大小与激光能量密度成近似正比。增透膜一般为双面镀 ,分前后膜堆两种情况 ,前膜堆表现为孔洞和疤痕 ,与高反膜相似 ;后膜堆为孔洞型的小圆麻点聚积 ,麻点处的薄膜完全剥落 ,没有疤痕等烧伤痕迹 ,是激光在基片之间形成的驻波电场损毁 ,损伤阈值比前膜堆低 1 5倍 ,决定着增透膜的损伤阈值。偏振膜的低能量密度损伤与增透膜后膜堆相似 ,表现为孔洞型小麻点聚积 ,损伤处未见疤痕等烧蚀痕迹。对薄膜小尺度损? 相似文献
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响应度R是反映探测器性能的一项重要指标,当探测器被强激光损伤后,光电探测器的响应度将发生改变。设计了一套实时测量探测器响应度的装置,用能量逐渐增加的Nd∶YAG激光辐照PIN光电探测器,获得了探测器响应度与入射强激光功率密度的变化关系。从实验数据可知,探测器被功率密度低于7.6×105W/cm2的激光辐照后不会发生损伤,探测器对532nm参考光的响应度不变;当激光的功率密度超过1.27×106W/cm2时,激光辐照后,探测器对532nm参考光的响应度开始下降,当探测器被功率密度为6.01×106W/cm2的激光辐照后,响应度迅速下降,PN结遭到破坏是探测器响应度下降的根本原因,扫描电镜的结果与我们的分析相一致。 相似文献
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A multi-conjugate adaptive optics (MCAO) can offer a possibility of widening field of view (FOV) characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle's expressions of two deformable mirrors (DMs) MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance. 相似文献
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Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use. 相似文献
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A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands. 相似文献
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40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm. 相似文献
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Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser. 相似文献
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Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored. 相似文献
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Xin Kang 《中国光学快报(英文版)》2008,6(2)
An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography. 相似文献
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The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films. 相似文献
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References: 《声学学报:英文版》2008,27(1):85-96
Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation. 相似文献