激光辐照行间转移型CCD的串扰效应

在采用一束激光辐照电荷耦合器件(Charged Coupled Device,CCD)图像传感器时,串扰效应是最重要的干扰之一.本文采用532 nm激光对一个行间转移型CCD进行辐照实验,观测到了一系列串扰现象,计算CCD的饱和阈值为0.32 mW/cm2.根据行间转移型CCD的工作原理和驱动脉冲时序,将串扰效应分为积...     

CCD中的激光光斑阴影现象及机理

对CCD相机在激光辐照下的暂时性失真问题进行了研究.用532 nm连续激光辐照以线阵CCD为图像传感器的Piranha HS-41-02K30相机进行了实验,实验发现,激光光斑和3个与其大小、形状皆相似的暗斑同时、等间距地出现于感光阵列方向上.这些暗斑即为CCD相机在激光辐照下的一种暂时性失真现象,本文称这3个暗斑为光斑阴影.根据实验数据分析了这一现象的规律和产生机理.分析认为,CCD图像传感器4个并行读出电路因共用同一偏置源而相互影响是产生光斑阴影现象的内在机制.推导了共偏置并行电路信号之间相互影响的关系式,由得到的关系式可知,降低公共偏置源与并行读出电路公共节点之间的电阻可减弱上述阴影失真现象;而用4个电压源分别为并行读出电路提供偏置,可以消除这种光斑阴影现象.本文推导的共偏置并行电路影响关系式不仅可解释阴影现象,也可为设计CCD器件时减弱或消除阴影失真提供借鉴.     

CCD光敏面上规则点阵的产生机理

采用1064 nm激光辐照可见光面阵CCD时,在其光敏面上观察到了规则点阵,相邻格点的间距约为99.38μm.改变激光的入射参数发现,规则点阵的产生与激光的入射能量、束散角和入射角无关,而与激光的波长有关,532,632,670和780 nm激光辐照时均没有观察到规则点阵的出现.更换不同型号的CCD,像元尺寸由3.75...     

切向空气气流对激光烧蚀碳纤维复合材料过程的影响

研究了靶材表面存在和不存在切向空气气流时,975 nm连续激光对碳纤维增强树脂基复合材料的辐照效应.两种情况卜靶材的动态响应过程明显不同,没有切向气流时,激光辐照1.28 s后,向外喷出的热分解产物在空气中燃烧,出现火焰同时伴有浓烟;有切向气流时,没有观察到带火焰和浓烟的燃烧现象,而是在激光辐照后的瞬间,激光作用区出现...     

激光在石英棱镜中的色散特性研究

对激光在石英棱镜中的色散现象给出了定性解释。在获得紫外、深紫外激光输出的实验中,对输出激光需用棱镜来分光观测,实验中发现,266nm与213nm在一定距离处的分离距离比532nm与266nm的分离距离还要大。对此现象,从熔融石英的Sellmeier色散方程出发,利用分光棱镜模型给出了定性解释,对实验现象提供了理论支持。     

采用马赫-曾德尔干涉法测量单晶硅在线应力损伤

开展了毫秒脉冲激光辐照单晶硅的实验研究,基于马赫-曾德尔干涉技术测量了毫秒脉冲激光与单晶硅相互作用过程中的在线应力损伤。用COMSOL Multiphysics有限元仿真软件建立了毫秒脉冲激光辐照单晶硅的数值仿真模型。从理论和实验两方面探讨了毫秒脉冲激光与单晶硅作用时,相同脉宽不同能量密度下应力场随时间的演变规律。进一步研究了干涉条纹的处理方法,基于传统x轴投影法提出了用45°投影法来计算材料各方向上的应变,并对两种处理方法得到的实验结果进行了对比。结果显示:与仿真结果相比,x轴投影法实验结果的误差为9.5%~29.3%,而45°投影法实验结果的误差为0.1%~22.6%,表明用马赫-曾德尔干涉法测量激光辐照单晶硅产生的在线应力损伤时,采用45°投影法计算材料各方向上的应变结果更为准确。该实验和计算方法为单晶硅在线应力损伤的研究提供了理论和实验上的指导。     

TEA CO2长波红外激光对红外凝视成像系统探测器组件的损伤效应

为了探究长波红外激光对红外凝视成像系统HgCdTe红外探测器组件的损伤机理,在ANSYS软件仿真研究的基础,开展了9.3μm激光对HgCdTe红外探测器损伤效应实验.通过利用ANSYS软件建立了激光辐照HgCdTe红外探测器的有限元理论仿真模型,获得了9.3μm脉冲CO2激光照射下探测器模型的温升分布,以是否达到熔融温...     

重复脉冲激光造成扫描型CCD背景条纹的规律

为了描述重复脉冲激光使扫描型CCD输出视频产生背景条纹的规律,基于这种背景条纹现象的产生机理对理想矩形脉冲激光产生的条纹建立了数学描述模型.通过该模型,可根据相机的时间延迟积分级数、单级积分时间和激光脉冲的脉宽、脉冲重复周期等参量之间的关系来判断背景条纹能否出现并计算背景条纹的尺寸参量,计算精确度为1 pixel.利用重复皮秒脉冲激光和日光灯分别辐照扫描型CCD进行了实验,验证了上述模型计算结果的正确性.在该模型的基础上,结合背景光强与脉冲散射光强的关系,给出了条纹可见度的表达式,并通过实验验证了该表达式所反映出的条纹可见度随着相关参量变化的规律.     

用于测量激光等离子体X射线的椭圆弯晶谱仪

研制了一种椭圆弯晶谱仪用于测量0.44～0.81 nm激光等离子体X射线光谱.该谱仪采用X射线CCD作探测器,用PET(2d＝0.874 nm)晶体作色散和聚焦元件,将晶体弯曲并粘贴在离心率和焦距分别为0.9586和1350 mm的椭圆形不锈钢基底上.对该谱仪在"星光Ⅱ"激光装置上进行了打靶实验,实验结果表明其光谱分辨率接近1000.     

激光显示的原理与实现

基于三基色激光显示具有亮度高、色彩鲜艳、清晰度高等特点,给出了大屏幕激光显示技术的原理,介绍了本实验室应用波长分别为671 nm、532 nm和473 nm,功率为1.3 W,0.32 W和3.5 W的红、绿、蓝固态激光器制造的大屏幕激光彩色电视。针对激光显示中干涉散斑现象和颜色失真提出的瞬间小视场变波前消干涉方法和颜色扩展方法,在实验中取得了良好效果。     

超短脉冲激光与介质相互作用过程中光学特性的变化

根据雪崩离化模型,分析了飞秒激光脉冲与介质材料相互作用过程中光学特性的变化规律。由于多层膜光学元件的光学特性与材料的折射率密切相关,当飞秒激光照射介质材料时,折射率会随着电场强度分布呈现不同程度的减小,从而会影响光学元件的性能。文中计算了飞秒激光照射多层膜光学元件时的透射光谱曲线,结果表明薄膜材料在发生不可逆损伤之前,光学元件的光谱特性已经发生变化。     

智能变电站中OTDR系统激光脉冲电路的设计及应用

针对智能变电站的光纤通信延时测量问题,对智能变电站中OTDR的工作原理和光源器件进行了研究,分析了激光脉冲频率和脉宽对系统性能的影响。根据激光二极管的发光机理与特点设计出了一套基于STM32控制单元的适合智能变电站中OTDR工作的激光驱动电路,重点分析了驱动电路中的调制电流,考虑了驱动电路对激光器的保护,并利用所设计的激光驱动电路搭建了简易OTDR观察光纤的损耗特性。研究结果表明,该电路可扩大激光脉冲频率和脉宽的调整范围,实现激光脉冲宽度最小可达300 ns,脉冲频率最大为50 KHz,激光发射功率为3 MW;通过实验,验证了光在光纤中的衰减特性,证实了该电路能满足实际智能变电站中OTDR工作所需,具有一定的参考价值。     

Quantitative atom probe analyses of rare-earth-doped ceria by femtosecond pulsed laser

We have investigated the irradiation conditions of femtosecond laser pulses for quantitative atom probe analyses of rare-earth (RE) doped ceria. The influence of laser wavelength, power, pulse frequency, as well as specimen temperature on mass resolution and background noise of atom probe mass spectra were investigated. Furthermore, quantitative atom probe analysis of yttrium distribution in Y-doped ceria was carried out with the optimized evaporation conditions. The distribution of yttrium was found to be uniform within the grains, but they were confirmed to be segregated at grain boundaries.     

基于皮秒激光烧蚀的氧化铟锡纳米颗粒制备系统

液相脉冲激光烧蚀法合成纳米颗粒是一种绿色环保的制备方法。基于该方法搭建了一套氧化铟锡(ITO)纳米颗粒制备系统,该系统采用皮秒激光作为光源辐照去离子水中的氧化铟锡固体靶材,最终合成出ITO纳米颗粒。随着入射脉冲能量的增加及激光辐照时间的增长,激光烧蚀效率明显增大,ITO产量增多。采用扫描电子显微镜(SEM)及X射线能谱仪(EDS)对制备的ITO纳米颗粒进行表征,所制备的纳米颗粒不含除铟(In)、锡(Sn)之外的杂质成分,纯度较高且72%的ITO纳米颗粒粒径大小在20～50 nm之间。     

基于非线性偏振旋转锁模技术的光纤飞秒激光振荡器

基于非线性偏振旋转（nonlinear polarization rotation, NPR）锁模机制的光纤激光器因其结构紧凑、可靠性高而备受关注。基于这一锁模原理设计并搭建了掺镱光纤飞秒激光器。当双向泵浦功率为380 mW,在1 030 nm波段获得了基频重复率为22.8 MHz的锁模脉冲。脉冲宽度为224 fs,平均功率180 mW,单脉冲能量8 nJ,10 dB带宽约为40 nm,信噪比大于50 dB。该激光器采用环形腔结构产生稳定的锁模飞秒脉冲输出,可实现自启动锁模。泵浦功率增加到1.6 W可观察到最高三阶被动谐波锁模,三次谐波对应68.5 MHz重复频率。该激光器由于在线宽、脉宽、脉冲能量上的优势,在光谱测量、拉曼成像等领域具有应用意义。     

引信激光装定用脉冲半导体激光器电源设计

在引信激光装定系统中，针对引信装定信息时脉冲半导体激光器，电源激光频率可调（PFM）、功率可调（PPM）的要求，结合半导体激光器的工作特性，设计一种以单片机（MCU）为控制芯片，以晶体三极管与场效应管为窄脉冲驱动电路的大功率半导体激光器电源。同时为电源驱动电路设计了DC-DC变换器。其中，激光频率设置为连续可调，激光器的驱动电流6～30A连续可调。该电源已应用于引信激光装定系统中，通过仿真与实验验证，该激光器电源工作正常、性能稳定。     

Effects of Er,Cr:YSGG laser parameters on dentin bond strength and interface morphology

Previous studies have shown the effects of Er,Cr:YSGG laser irradiation on the dentin bond strength; but there are few reports that show the significance of the irradiation with different laser parameters on dentin bond strength and interface morphology. This in‐vitro study attempted to evaluate the microtensile bond strength (μTBS) and interface morphology of resin‐dentin interfaces, either followed by treatment with Er,Cr:YSGG laser irradiation with different parameters or not. The flattened dentin samples of 35 bovine teeth were embedded into acrylic blocks and randomly divided into seven groups according to surface treatments using Er,Cr:YSGG lasers with different parameters: 3 W/20 Hz, 3 W/35 Hz, 3 W/50 Hz, 1.5 W/20 Hz, 1.5 W/35 Hz, 1.5 W/50 Hz, or no laser treatment (n = 5). Composite buildups were done over bonded surfaces and stored in water (24 hours at 37°C). Specimens were sectioned into sticks that were subjected to μTBS testing and observed under FE‐SEM. Control groups (27.70 ± 7.0) showed statistically higher values than laser‐irradiated groups. There were no significant differences among laser groups. Despite that, increasing the pulse frequency yielded slightly higher bond strength. Depending on laser settings, Er,Cr:YSGG laser irradiation caused interfacial gaps and resin tags with wings morphology. With the parameters used in this study, Er,Cr:YSGG laser irradiation promoted morphological changes within resin‐dentin interfaces and negatively influenced the bond strength of adhesive systems. Microsc. Res. Tech. 78:1104–1111, 2015. © 2015 Wiley Periodicals, Inc.     

Thermal alteration and morphological changes of sound and demineralized primary dentin after Er:YAG laser ablation

The purpose of this study was to assess the influence of Er:YAG laser pulse repetition rate on the thermal alterations occurring during laser ablation of sound and demineralized primary dentin. The morphological changes at the lased areas were examined by scanning electronic microscopy (SEM). To this end, 60 fragments of 30 sound primary molars were selected and randomly assigned to two groups (n = 30); namely A sound dentin (control) and B demineralized dentin. Each group was divided into three subgroups (n = 10) according to the employed laser frequencies: I-4 Hz; II-6 Hz, and III-10 Hz. Specimens in group B were submitted to a pH-cycling regimen for 21 consecutive days. The irradiation was performed with a 250 mJ pulse energy in the noncontact and focused mode, in the presence of a fine water mist at 1.5 mL/min, for 15 s. The measured temperature was recorded by type K thermocouples adapted to the dentin wall relative to the pulp chamber. Three samples of each group were analyzed by SEM. The data were submitted to the nonparametric Kruskal-Wallis test and to qualitative SEM analysis. The results revealed that the temperature increase did not promote any damage to the dental structure. Data analysis demonstrated that in group A, there was a statistically significant difference among all the subgroups and the temperature rise was directly proportional to the increase in frequency. In group B, there was no difference between subgroup I and II in terms of temperature. The superficial dentin observed by SEM displayed irregularities that augmented with rising frequency, both in sound and demineralized tissues. In conclusion, temperature rise and morphological alterations are directly related to frequency increment in both demineralized and sound dentin.     

Autofluorescence spectroscopy and imaging of Platymonas subcordiformis irradiated by diode laser based on LSCM

Autofluorescence spectra and optical imaging of Platymonas subcordiformis after irradiation of diode laser were observed via laser scanning confocal microscopy (LSCM). With 488 nm Ar(+) laser excitation, the horizontal and vertical dimensions of a cup-shaped chloroplast of the irradiation group increased about 10% compared with the control group. The fluorescence spectra were similar between irradiation group and control group with a maximum fluorescence band around 682 nm, whereas the former has a higher intensity. Image of a small circular substance with stronger two-photon autofluorescence (TPA) was obtained when using two-photon excitation wavelength of 800 nm in single-channel mode. Further analysis by the 800 nm excitation based on two independent-channels mode showed an emission band of the small circular substance around 376-505 nm, which corresponded to the eyespot of P. subcordiformis. In lambda scanning mode, with two-photon wavelength of 800 nm excitation, six fluorescence peaks that are located at 465, 520, 560, 617, 660 and 680 nm were observed; the fluorescence intensity of the irradiation group was higher than that of the control group, especially at 520, 560 and 617 nm. As a conclusion, diode laser irradiation can promote chloroplast growth of P. subcordiformis cells in the form of expanding area and the increasing content of protein, phospholipids and chlorophyll. LSCM, especially TPA imaging based on femtosecond laser excitation, provides a nondestructive, real-time and accurate method to study changes of living algal cells under laser irradiation and other environmental factors.