单CCD彩色相机激光干扰模型及外场干扰实验

开展了多波段激光(750~970 nm)对彩色CCD成像系统的外场干扰实验,测得了不同辐照条件下对外场1.3 km处彩色CCD成像系统的干扰效果;建立了彩色CCD相机的激光干扰模型,对实验结果进行了理论验证与分析。理论与实验结果表明:强激光对彩色CCD成像系统的干扰效果明显,CCD靶面出现了明显的光饱和和串扰现象,光饱和区域的形成是由激光束进入光学系统后发生衍射效应造成的;到靶激光功率密度越强,CCD靶面光饱和面积越大,激光干扰效果越好;单波段750 nm激光作用下,到靶功率密度为4.2 kW/cm²,CCD靶面的光饱和面积为0.88 mm×0.97 mm;多波段激光(750~970 nm)作用下,到靶功率密度为20.7 kW/cm²,CCD靶面发生全靶面饱和现象;仿真结果与实验结果基本一致,证明了理论模型的正确性。对远场干扰能力计算结果表明:随着干扰距离的增加,到靶功率密度减小,激光干扰效果变差。     

光学击穿对受激布里渊散射特性的影响

把雪崩电离模型引入受激布里渊散射模型中，数值模拟了无光学击穿和有光学击穿时受激布里渊散射能量反射率随输入光功率密度的变化规律.实验上选取净化和未净化的CCl₄作为散射介质，在Nd:YAG调Q激光系统中进行了验证，理论与实验符合得很好.结果表明：当无光学击穿时，随着输入光功率密度的增大，能量反射率先是非线性增大，然后缓慢增大趋于饱和；而当有光学击穿时，随着输入光功率密度的增大，能量反射率先是非线性增大，达到最高值之后开始下降，最终趋于零.无光学击穿时的能量反射率及其稳定度明显高于有光学击穿时的情况. 关键词： 受激布里渊散射 光学击穿 雪崩电离     

切向气流作用下玻璃纤维复合材料的激光辐照效应

实验研究了样品表面有切向空气气流、切向氮气气流和无气流时,976 nm连续激光对玻璃纤维增强E-51环氧树脂复合材料的辐照效应。结果表明:无气流时,喷出的热分解产物会对入射激光产生屏蔽作用;有气流时,激光对玻璃纤维的破坏方式是其升温熔化后再被切向气流带走;当激光功率密度较低时,切向空气气流以加强样品表面的对流冷却作用为主,不利于激光对玻璃纤维复合材料的破坏;当激光功率密度较高时,切向空气气流以降低屏蔽作用和提供氧气助燃为主,有利于激光对玻璃纤维复合材料的破坏。三种气流状态下,质量损失随功率密度呈现单调增加趋势,当入射激光功率密度在100~600 W/cm2范围内,随着功率密度的增大,激光能量的利用效率逐渐增大并趋于稳定。     

超强激光功率密度对等离子体中自生磁场和电子热传导的影响

应用多光子非线性康普顿散射模型、3维粒子模拟模型和数值计算方法,研究了超强激光与等离子体作用中自生磁场产生和电子热传导过程,提出了将非线性康普顿散射光作为改变等离子体自生磁场和电子热传导的新机制,给出了自生磁场最大饱和值和超热电子热传导的修正方程和数值计算结果。研究发现在时间为100~160范围内,自生磁场能量随入射激光功率密度增大而迅速增大,之后处于较高饱和阶段。增大的初始时刻较散射前提前了20,增大阶段的时间延长了30,饱和阶段增幅为40。入射激光功率密度为1019~1020W/cm2时,自生磁场强度最大模拟值为1.47104~3.75104T,单电子能谱峰值出现在3.3MeV和6.6MeV附近,能谱曲线在4~15 MeV和11~14.3MeV范围迅速衰减,在6.7MeV和13.2MeV以上时,超热电子有效温度为2.6MeV和4.5MeV,比无散射的理论值和拟合值均有一定增大。随入射激光强度增大,热流随激光脉冲一起向等离子体内流动的时间缩短,自生磁场限制热流的时间延长。并对所得结果给出了初步物理解释。     

超强激光功率密度对等离子体中自生磁场和电子热传导的影响

应用多光子非线性康普顿散射模型、3维粒子模拟模型和数值计算方法,研究了超强激光与等离子体作用中自生磁场产生和电子热传导过程,提出了将非线性康普顿散射光作为改变等离子体自生磁场和电子热传导的新机制,给出了自生磁场最大饱和值和超热电子热传导的修正方程和数值计算结果。研究发现在时间为100~160范围内,自生磁场能量随入射激光功率密度增大而迅速增大,之后处于较高饱和阶段。增大的初始时刻较散射前提前了20,增大阶段的时间延长了30,饱和阶段增幅为40。入射激光功率密度为1019~1020W/cm2时,自生磁场强度最大模拟值为1.47104~3.75104T,单电子能谱峰值出现在3.3MeV和6.6MeV附近,能谱曲线在4~15 MeV和11~14.3MeV范围迅速衰减,在6.7MeV和13.2MeV以上时,超热电子有效温度为2.6MeV和4.5MeV,比无散射的理论值和拟合值均有一定增大。随入射激光强度增大,热流随激光脉冲一起向等离子体内流动的时间缩短,自生磁场限制热流的时间延长。并对所得结果给出了初步物理解释。     

宽带KrF激光抽运的受激布里渊散射反射率研究

实验上研究了宽带KrF激光抽运的受激布里渊散射(SBS)随抽运功率密度、介质气压和透镜焦距这三个实验参数的变化规律.在较低的抽运功率密度情况下，SBS反射率随抽运功率密度呈非线性增长；当抽运功率密度提高到一定程度，SBS反射率接近饱和；当功率密度继续增大，SBS 反射率随之下降.介质气压提高能够促进SBS的转换.透镜焦距长度的变化使SBS饱和反射率存在一峰值.理论上建立了宽带多模SBS模型，数值模拟结果与实验结果符合得很好，解释了宽带SBS反射率对实验参数的变化规律. 关键词： 宽带 KrF激光 受激布里渊散射(SBS) 反射率     

激光诱导多孔硅晶格畸变的Raman光谱和光致发光谱研究

研究了掺钛水热法制备多孔硅的Raman光谱和光致发光谱.实验发现,当激光功率较低时,多孔硅的Raman光谱在略低于520cm^-1附近表现为一锐的单峰,和晶体硅的Raman光谱类似.随激光功率增大,该单峰向低波数移动,Raman和光致发光峰的强度与激光强度的一次方成正比.当激光功率增大到一定值时,该单峰分裂成两个Raman峰,光致发光谱的强度突然增大,与激光强度之间不再满足一次方的关系,位于低波数一侧的Raman峰随激光功率增大进一步向低波数移动.多孔硅Raman光谱随激光功率的变化是 关键词： 多孔硅 Raman光谱 光致发光     

紫外光激发下氧化锌纳米线的发光特性研究

室温条件下,用355 nm的激光激发氧化锌纳米线,测量了其发光光谱.观察到半宽度较小、峰值波长约382 nm的紫光峰和半宽度较宽、峰值波长约507 nm的绿光峰;两峰的发光强度随激发光功率密度的变化而变化,且均存在饱和效应,但各自的变化规律及饱和值的大小不同;紫光峰的中心波长随激发光功率密度的增加而发生了明显的红移.对两峰产生的机理、强度饱和值存在的原由、强度随激发光功率密度变化及紫光峰红移的起因进行了分析.     

超强激光功率密度对等离子体中自生磁场和电子热传导的影响

应用多光子非线性康普顿散射模型、3维粒子模拟模型和数值计算方法,研究了超强激光与等离子体作用中自生磁场产生和电子热传导过程,提出了将非线性康普顿散射光作为改变等离子体自生磁场和电子热传导的新机制,给出了自生磁场最大饱和值和超热电子热传导的修正方程和数值计算结果 .研究发现在时间为100~160内,自生磁场能量随入射激光功率密度增大而迅速增大,之后处于较高饱和阶段.增大的初始时刻较散射前提前了20,增大阶段的时间延长了30,饱和阶段增幅为40%.入射激光功率密度为1019~1020W/cm2时,自生磁场强度最大模拟值为1.47×104~3.75×104T,单电子能谱峰值出现在3.3 Me V和6.6 Me V附近,能谱曲线在4~15 Me V和11~14.3 Me V迅速衰减,在6.7 Me V和13.2 Me V以上时,超热电子有效温度为2.6 Me V和4.5 Me V,比无散射的理论值和拟合值均有一定增大.随入射激光强度增大,热流随激光脉冲一起向等离子体内流动的时间缩短,自生磁场限制热流的时间延长.对所得结果给出了初步物理解释.     

非平衡气流与化学激光的增益饱和效应

提出气流与化学激光的“对流-非平衡交叉弛豫”的理论。对于气流介质的湍流和层流混合两类流动模型,分别导出了增益系数和饱和增益谱的表示式;得到了一些新的饱和规律;非饱和增益和饱和增益均与流向距离有关。具有Doppler加宽的饱和放大器的增益线形,呈现非均匀和均匀加宽并存的“反常”现象。本理论与实验结果相符合。 关键词：     

横流放电CO2激光的理论分析

本文提出了横流放电CO₂激光器的理论分析模型,导出了稳态发射的基本方程式,得到与熟知的非流动稳态增益饱和及功率理论相同的简单解析关系式。关系式包含了流动效应及光腔上游泵浦效应的修正项。根据强度沿流动方向变化的分析,求得饱和强度等参量在提高流速时的极限值。本文分析为文献[1—3]建议的选择平均增益系数并利用非流动稳态关系计算流动激光器特性的半经验方案提供了理论证明,同时将文献[4]提出的流动激光器的定性分析发展为定量计算。由于本文公式的简单性与非流动情况一样,因而本理论能够取代半经验方案。 关键词：     

Design considerations and scaling laws for high power convective cooled CW CO2 lasers

Various criteria for designing high power convective cooled CO₂ lasers have been discussed. Considering the saturation intensity, optical damage threshold of the optical resonator components and the small-signal gain, the scaling laws for designing high power CW CO₂ lasers have been established. In transverse flow CO₂ lasers having discharge of square cross-section, the discharge lengthL and its widthW for a specific laser powerP (Watt) and gas flow velocityV (cm/s) can be given byL = 1.4 x 10⁴ p ^1/2 V ^-1 cms andW = 0.04P ^1/2 cms. The optimum transmitivity of the output coupler is found to be almost constant (about 60%), independent of the small signal gain and laser power. In fast axial flow CO₂ lasers the gas flow should be divided into several discharge tubes to maintain the flow velocity within sonic limit. The discharge length in this type of laser does not depend explicitly on the laser power, instead it depends on the input power density in the discharge and the gas flow velocity. Various considerations for ensuring better laser beam quality are also discussed.     

基于振动弛豫理论提高光抽运太赫兹激光器输出功率的研究

以半经典密度矩阵理论和分子振动弛豫理论为基础,研究添加适当比例缓冲气体与适当减小波导芯径对光抽运太赫兹激光器输出光强的影响.计算结果表明,加入适当比例缓冲气体或适当减小波导的芯径均能提高太赫兹激光的输出光强;同时优化两个参数能进一步提高抽运激光能量转化为太赫兹激光能量的效率,延长工作腔中的有效激活区,延缓抽运饱和效应的出现,提高太赫兹激光输出光强.该研究对提高光抽运太赫兹激光器的能量转化效率、提高光抽运太赫兹激光器的输出功率及实现光抽运太赫兹激光器的小型化有重要的指导意义.     

Gain and saturation intensity parameters in a transverse-flow CO2 laser

Details of an experimental investigation of the output characteristics of the 1.2 kW cw transverse-flow, electrically excited CO₂ laser are presented. They were used for estimation of the saturation intensity and the laser cavity loss values, as they follow from the Rigrod-type model of laser operation. The saturation intensity parameter was calculated from measurements of the output power and small signal gain performed with the same experimental conditions. Measurements of the small signal gain were conducted at different points along the gas flow direction for several laser operational parameters described by gas pressure and input electrical power.     

Pressure Dependence of the Small-Signal Gain and Saturation Intensity of a Copper Bromide Laser

A pair of copper bromide lasers in an oscillator-amplifier configuration is used to investigate the small signal gain and saturation intensity as amplifying parameters and output power of lasers, versus pressure of buffer gas. It is shown that the amplifying parameters and laser output power have a maximum value at optimum buffer gas pressure of 11 Torr. The challenge between microscopic parameters such as stimulated emission cross section, laser upper level lifetime, and population inversion, which determine the values of laser characteristics respective to the operational pressure of buffer gas, are investigated. Thus an optimum delay time of about 10 ns is determined, and a maximum output power equivalent to about 12 W is extracted. The amplifying parameters and measured output power of laser versus delay times show some local maxima and minima at the delay time interval of 6-43 ns.     

The bi-directional amplifier in the constant intensity approximation and its application to KrF lasers

Bi-directional and folded laser amplifiers are analysed in the constant intensity approximation. Simple analytical expressions are developed for gain, output intensity and extraction efficiency. The analysis is applied to electron-beam pumped KrF lasers and expressions for saturation intensity, small-signal gain coefficient and intrinsic efficiency in terms of gas composition and pump power per unit volume are given. The problem of fluorine burn-up in KrF lasers is discussed. Under certain conditions the analysis is shown to be equally applicable to oscillators and comparison is made with previous experimental results and computer code predictions.     

Parametric study of plasma active medium and gain saturation region in a Ne-like soft X-ray laser

Plasmas created by the interaction of high power optical laser with a target surface can be used as a source of soft X-ray lasers. Plasma and pump laser characteristics play significant role in achieving high gain coefficient for such plasma based on soft X-ray lasers. In the present work, the plasma active medium parameters for germanium element at a wavelength of 19.6 nm irradiated by a double-pulse pump laser have been studied using MED103 hydrodynamic code. For this purpose, first, the effects of laser intensity, pulse width and delay time of two pulses on the gain coefficient have been investigated and the optimum conditions for the maximum gain extent of Ne-like germanium soft X-ray laser are obtained. Then, in order to calculate the intensity of such high gain lasers in which Linford equation is invalid, we have adopted the general formula of amplified spontaneous emission intensity, which is valid in all range of intensities even at much higher intensities than saturation intensity. Finally, the soft X-ray laser intensities in the saturated areas for different plasma lengths have been calculated. The results show that the output of soft X-ray laser intensity with 294 cm⁻¹ gain coefficient can reach to about several times saturated intensity by applying a 1–2 mm plasma length as the active medium.     

Yb:CNGG有源反射镜的多程放大特性研究

高效、高平均功率固体纳秒脉冲激光器在光电对抗、激光雷达、材料改性、激光加工等诸多领域发挥着越来越重要的作用,然而目前大多数纳秒级高平均功率激光器采用Yb:YAG或掺Nd材料作为增益介质,材料的高饱和通量或低储能密度会导致激光器放大链路复杂,体积庞大。研究比较了一种更适合作为高平均功率、高脉冲能量激光器增益介质的无序石榴石晶体Yb:CNGG,研究了有源反射镜结构中Yb:CNGG的多程增益特性,分析了放大过程并建立了多程放大模型,在一定的泵浦条件下优化了晶体参数以实现更好的储能。开展了双程放大实验,在15 kW/cm²的泵浦功率密度下得到了1.53倍的增益。对比Yb:CNGG晶体与Yb:YAG晶体的多程放大能力,在相同的晶体参数和泵浦条件下,在入射能量1 mJ时Yb:CNGG可实现2.11 J的脉冲能量输出,优于Yb:YAG晶体1.41 J的能量输出。     

Semi-gas kinetics model for performance modeling of flowing chemical oxygen-iodine lasers (COIL)

The gas pressure in a laser cavity of flowing chemical oxygen-iodine laser (COIL)is about 133.31333 Pa[1]. In this pressure range, effects of homogeneous and inhomo-geneous broadening competing with each other on the performances of a COIL are no-ticeable. Generally, a rate equation (RE) model is adopted to the performance modeling of a supersonic COIL, such as in refs. [1—4]. This model assumes the spectral line pro-file is homogeneously broadened. Homogeneous broadening assumption sim…     

Modeling of flowing gas diode pumped alkali lasers: dependence of the operation on the gas velocity and on the nature of the buffer gas

A simple, semi-analytical model of flowing gas diode pumped alkali lasers (DPALs) is presented. The model takes into account the rise of temperature in the lasing medium with increasing pump power, resulting in decreasing pump absorption and slope efficiency. The model predicts the dependence of power on the flow velocity in flowing gas DPALs and checks the effect of using a buffer gas with high molar heat capacity and large relaxation rate constant between the P_3/22 and P_1/22 fine-structure levels of the alkali atom. It is found that the power strongly increases with flow velocity and that by replacing, e.g., ethane by propane as a buffer gas the power may be further increased by up to 30%. Eight kilowatt is achievable for 20?kW pump at flow velocity of 20 m/s.