对基于磁控溅射方法沉积的HfO_2薄膜的紫外光学特性及薄膜结构的研究（英文）

本文基于磁控溅射方法,功率从160 W增加到240 W,在石英衬底上沉积氧化铪薄膜(HfO_2),并对沉积后的薄膜进行退火处理.利用X射线衍射谱、X射线光电子能谱、紫外-可见-近红外透射谱和椭圆偏振仪对Hf02薄膜进行研究,对比了退火前后Hf02薄膜的光学特性及薄膜结构的变化.实验结果显示,HfO_2薄膜对波长大于200 nm的入射光具有很低的吸收系数.优化退火温度和时间,可以将沉积后的Hf02薄膜从非晶态转化成多晶态.退火有助于结晶生成和内应力的增加,同时退火可以优化薄膜的化学计量比,提升薄膜的光学密度及折射率.对功率在220 W左右沉积的薄膜进行退火,获得的Hf02薄膜具有较高并且稳定的光学折射率(2)和紫外光透射率,可在紫外波段减反膜系统中得到应用.     

化学法制备的HfO2薄膜的激光损伤阈值研究

 采用化学法制备了HfO₂介质膜，研究了热处理、紫外辐照以及Al₂O₃复合对HfO₂介质膜激光损伤阈值的影响。采用红外光谱（FTIR）和X射线衍射仪对薄膜进行了表征，并用输出波长为1.064 μm、脉宽为10 ns的电光调Q激光系统测试薄膜的激光损伤阈值。实验结果表明：采用150 ℃左右的温度对薄膜进行热处理可以提高薄膜的激光损伤阈值，所获得的薄膜的激光损伤阈值高达42.32 J/cm²，比热处理前的激光损伤阈值提高了82%；无机材料Al₂O₃的适量添加能够提高薄膜的激光损伤阈值，其中HfO₂与Al₂O₃的最佳质量配比约为95∶5；另外，对薄膜进行适当的紫外辐照也可改善HfO₂ 薄膜以及HfO₂-Al₂O₃复合薄膜的抗激光损伤性能。紫外辐照对提高HfO₂-Al₂O₃复合薄膜的激光损伤阈值效果尤为显著，辐照40 min后的激光损伤阈值达到44.33 J/cm²，比紫外辐照前的激光损伤阈值提高了90%。     

离子束辅助工艺中APS源偏转电压对HfO2薄膜性能的影响

 基于Leybold APS1104镀膜系统,采用离子束辅助反应沉积技术,以金属Hf粒为初始镀膜材料,APS源偏转电压为50~140 V范围内,在［100］单晶硅片和紫外石英（JGS1）基板上制备了HfO₂单层膜。分别利用Lambda 900分光光度计、X射线光电子能谱仪、X射线衍射仪以及原子力显微镜对HfO2薄膜的光谱性能、表面及纵向化学成分、晶相结构以及表面粗糙度进行了分析。结果表明：当APS源偏转电压在120~140 V及50~90 V两个范围内变化时,HfO2薄膜的紫外短波光学损耗随着偏转电压的降低而减小,而为110~90 V时紫外短波光学损耗对偏转电压的变化不敏感;偏转电压在50~140 V的范围内时,制备的HfO₂薄膜表面及纵向化学成分无明显变化;当偏转电压为100 V时,HfO₂薄膜晶粒尺寸及表面粗糙度分别达到最大值26.2 nm及5.79 nm,其后,随着偏转电压的降低,二者均逐渐减小。     

Cu掺杂Ga2O3薄膜的光学性能

采用射频磁控溅射和N₂气氛退火处理制备了多晶Ga₂O₃薄膜和Cu掺杂Ga₂O₃薄膜.用X射线衍射仪、紫外-可见分光光度计、荧光光谱仪对Ga₂O₃薄膜和Cu掺杂Ga₂O₃薄膜的结构和光学性能进行了表征.结果表明,Cu掺杂后Ga₂O₃薄膜的结晶质量变差,透过率明显降低,吸收率增加,光学带隙减小.本征Ga₂O₃薄膜在紫外、蓝光和绿光出现了发光带,Cu掺杂后紫外和蓝光发射增强,且在475 nm 处出现了一个新的发光峰.     

Zn掺杂β-Ga2O3薄膜的制备和特性研究

β-Ga₂O₃是一种宽带隙半导体材料,能带宽度E_g≈5.0eV,在光学和光电子学领域有广泛的应用。用射频磁控溅射方法在Si衬底和远紫外光学石英玻璃衬底制备了本征β-Ga₂O₃薄膜及Zn掺杂β-Ga₂O₃薄膜,用紫外 可见分光光度计、X射线衍射仪、荧光分光光度计对本征β-Ga₂O₃薄膜及Zn掺杂β-Ga₂O₃薄膜的光学透过、光学吸收、结构和光致发光进行了测量,研究了Zn掺杂和热退火对薄膜结构和光学性质的影响。退火后的β-Ga₂O₃薄膜为多晶结构,与本征β-Ga₂O₃薄膜相比,Zn掺杂β-Ga₂O₃薄膜的β-Ga₂O₃(111)衍射峰强度变小,结晶性变差,衍射峰位从35.69°减小至35.66°。退火后的Zn掺杂β-Ga₂O₃薄膜的光学带隙变窄,光学透过降低,光学吸收增强,出现了近边吸收,薄膜的紫外、蓝光及绿光发射增强。表明退火后Zn掺杂β-Ga₂O₃薄膜中的Zn原子被激活充当受主。     

退火对电子束热蒸发Al2O3薄膜性能影响的实验研究

 用电子束热蒸发方法镀制了Al₂O₃材料的单层膜，对它们在空气中进行了250~400 ℃的高温退火。对样品的透射率光谱曲线进行了测量，计算了样品的消光系数、折射率和截止波长。通过X射线衍射仪（XRD）测量分析了薄膜的微观结构,采用表面轮廓仪测量了样品的表面均方根粗糙度。结果发现随着退火温度的提高光学损耗下降，薄膜结构在退火温度为400 ℃时仍然为无定形态，样品的表面粗糙度随退火温度的升高而增加。引起光学损耗下降起主导作用的是吸收而不是散射，吸收损耗的下降主要是由于退火使材料吸收空气中的氧而进一步氧化，从而使薄膜材料的非化学计量比趋于正常。     

Fe掺杂氢化非晶碳薄膜制备及其热稳定性能

 以H₂、反式-2-丁烯（T₂B）和二茂铁混合气体为工作气体,用金属有机等离子体增强化学气相沉积法（PECVD）制备了Fe掺杂氢化非晶碳（a-C:H:Fe）薄膜。使用X射线光电子能谱（XPS）对a-C:H:Fe薄膜成分进行了分析。使用台阶仪、场发射扫描电镜（FESEM）、热重分析和紫外可见分光光度计（UV-VIS）,对比分析了a-C:H薄膜和a-C:H:Fe薄膜的沉积速率、表面形貌、热稳定性和光学带隙变化。研究表明：相同制备条件下,相比a-C:H薄膜,a-C:H:Fe薄膜的沉积速率高,表面颗粒小,容易碳化,光学带隙变窄。     

氧分压对ZrO2薄膜激光损伤阈值的影响

 在不同的氧分压下用电子束热蒸发的方法制备了ZrO₂薄膜。分别通过X射线衍射、光学光谱、热透镜技术、抗激光辐照等测试，对所制备样品的微结构、折射率、吸收率及激光损伤阈值进行了测量。实验结果表明，薄膜中晶粒主要是四方相为主的多晶结构，并且随着氧分压的增加，结晶度、折射率以及弱吸收均逐渐降低。薄膜的激光损伤阈值开始随着氧分压增加从18.5J/cm²逐渐增加，氧分压为9×10^-3Pa时达到最大，值为26.7 J/cm²，氧分压再增加时则又降低到17.5 J/cm²。由此可见，氧分压引起的薄膜微结构变化是ZrO₂薄膜激光损伤阈值变化的主要原因。     

ZnO-SnO2透明导电薄膜的制备及性能研究

采用二步成胶工艺制备ZnO-SnO₂透明导电薄膜,应用X射线衍射、原子力显微镜、紫外-可见分光光度计、薄膜分析仪及四探针仪等对薄膜的结构、表面微观形貌、透过率和导电性能进行表征.结果表明,锌锡摩尔比为9/12,退火温度为500 ℃时,薄膜的透过率达90%,电阻率为3.15×10-3 Ω·cm.与其它工艺相比,二步成胶工艺所制备出的ZnO-SnO₂透明导电薄膜性能优异.     

SrF2-CaF2混合物薄膜的物理及红外光学特性研究

采用热蒸发和电子束蒸发两种沉积方式分别沉积了相同厚度的SrF₂-CaF₂ (比例为1∶1) 的混合物薄膜,对其物理和光学特性进行了研究,并定量地给出了其在红外波段的光学常数,填补了这一数据的空白. 同时提供了一种获得不同低折射率薄膜的方法.文中还以该比例的混合物作为低折射率材料,研制出具有很好的光学性能的长波红外宽光谱增透膜.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

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.     

Quick single-photon detector with many avalanche photo diodes working on the time division

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.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

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.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

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.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

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.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

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.     

An effective method for reducing speckle noise in digital holography

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.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

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.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

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.