Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Conceptual Design for Glass Cavity in Nd∶Glass Slab Amplifier
No full text针对片状放大器片腔的洁净度问题,提出一种钕玻璃片状放大器玻璃腔的设计方案.选用滤紫外石英玻璃作为主框架的材料,对玻璃腔的结构和密封方案进行设计,并利用玻璃腔外表面镀金属材料的方式进行遮光.采用神光Ⅱ升级主放和100片状放大器进行不同腔体的洁净度对比试验,结果表明玻璃腔的洁净度较不锈钢腔提高了近70%.运用光学高级系统分析程序对玻璃腔进行光线追迹,其钕玻璃泵浦比例提高了8.84%.该方案不仅能减少腔内气溶胶的产生,还能提高钕玻璃泵浦比例.国家自然科学基金; 惯性约束聚变能源先期关键技术合作研究To overcome the problem of cleanliness in the laser's internal cavity, a glass cavity design for a Nd:glass slab amplifier was proposed, which uses UV-stop quartz glass for its main structure.The design of the main structure of the glass cavity and the sealing are optimized, and metal-coated surfaces are used to prevent light from escaping.The cleanliness of the stainless steel cavity of the slab amplifier of the SG-II-UP laser and the glass cavity of a 100 slab amplifier were compared; the cleanliness of the glass cavity was found to be 70% better than that of the stainless cavity. Further, advanced system analysis program was used to simulate the designed amplifier, with the pumping ratio of the Nd:glass in the glass cavity being increased by 8.84%.Thus, the glass cavity decreases the production of aerosols and enhances the pumping ratio of the Nd∶glass
Far-field detection system for laser beam and crystal alignment
No full textNational Natural Science Foundation of China [61205137]Laser beam far-field alignment as well as frequency-doubling and frequency-tripling crystal adjustment is very important for high-power laser facility. Separate systems for beam and crystal alignment are generally used while the proposed approach by off-axial grating sampling share common optics for these two functions, reducing both space and cost requirements. This detection system has been demonstrated on the National Laser Facility of Israel. The experimental results indicate that the average far-field alignment error is <5% of the spatial filter pinhole diameter, average autocollimation angle error of crystals is <10 mu rad, and average frequency-tripling conversion efficiency is 69.3%, which meet the alignment system requirements on the beam direction and crystals. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE
Lens-free coherent modulation imaging with collimated illumination
No full textChinese Academy of Sciences, China [902012312D1100101]; [29201431151100301]We propose a lens-free coherent modulation imaging (CMI) method for reconstructing a general complex-valued wave field from a single frame of a diffraction pattern. A numerical Fourier transform is introduced in the iterative reconstruction process to replace the lens or zone plate used in the current CMI technique to adopt the constraint on the Fourier components of the exit wave field of the sample. While the complexity of the experimental setup is remarkably reduced by replacing the zone plate and additional accessories with the numerical processing, the energy fluence loss induced by the undesired diffraction orders of the zone plate can be also avoided. The feasibility of the proposed technique is verified experimentally with visible light
Research on Calculation of Gain Spatial Distribution for Main Amplifiers in Million Joules Laser Facility
No full text基于蒙特卡罗算法及ASAP光学软件构建了完整分析万焦耳级激光主放大器抽运动力学过程的模型。该模型包含三维空域和一维时域,分析计算了包层完全吸收时不同抽运时刻通光面上的储能分布,其变化趋势与文献报道结果相同,验证了建模的正确性。通过对比包层完全吸收和部分剩余反射时的平均小信号增益系数,发现当剩余反射率低于0.05%时,两者区别并不明显。考虑包层部分反射后平均小信号增益系数的计算值比测量值4.42/m偏小6%,分析其原因主要在于模型计算过程中的采用部分近似、未考虑自发辐射的光谱宽度以及钕玻璃中存在的亚表面缺陷国家自然科学基金A model which can simulate the pump dynamics process of the main amplifiers in million joules laser facility is built based on Monte Carlo algorithm and a ASAP software. The model contains 3D airspace and 1D time domain, and the evolution of the distribution of the energy in light pass surface in different pumping time with complete absorption on cladding is calculated, which is the same with the results mentioned in previous articles proving the accuracy of the model. The comparisons of average small signal gain coefficient are made between the cases when the residual reflection in cladding is taken into consideration or not. The results show that there is no significant difference when residual reflectivity is below 0.05%. The value of calculated average small signal gain coefficient with residual reflection is 6 percentage smaller than the measured value(4.42/m), which results from the use of part approximation during the simulation, the unconsidered spectrum of spontaneous radiation,the subsurface damage in the actual Nd:phosphate glass and so on
Simulation study of broadband long-pulsed amplification in high-power laser systems
No full textNational Natural Science Foundation of China [61205212]Accurately and efficiently predicting the fundamental-frequency temporal shape of broadband long-pulsed lasers is very important in research on the properties of high-power laser amplifiers. In this study, we first propose that analytic electric polarization in the temporal domain is applied to broadband long-pulsed pulse amplification. We first verify the accuracy of this algorithm in the dozens of picoseconds range and the results are consistent with Miro software. Then we simulate the broadband long-pulsed amplification. The simulation results indicate that the front edge of the output pulse is more enlarged than the end edge owing to saturation and that the gain narrowing induces severe amplitude modulation. Analytic electric polarization in the temporal domain is effective and precise for investigating the broadband pulse amplification in the time scale from dozens of picoseconds to nanoseconds, and the computation time can be decreased by at least 4 orders of magnitude
Suppression of FM-to-AM modulation by polarizing fiber front end for high-power lasers
No full textNational Natural Science Foundation of China (NSFC) [61205103, 61405211]FM-to-AM modulation is an important effect in the front end of high-power lasers that influences the temporal profile. Various methods have been implemented in standard-fiber and polarization-maintaining (PM)-fiber front ends to suppress the FM-to-AM modulation. To analyze the modulation in the front end, a theoretical model is established and detailed simulations carried out that show that the polarizing (PZ) fiber, whose fast axis has a large loss, can successfully suppress the modulation. Moreover, the stability of the FM-to-AM modulation can be improved, which is important for the front end to obtain a stable output. To verify the model, a PZ fiber front end is constructed experimentally. The FM-to-AM modulation, without any compensation, is less than 4%, whereas that of the PM fiber front end with the same structure is nearly 20%. The stability of the FM-to-AM modulation depth is analyzed experimentally and the peak-to-peak and standard deviation (SD) are 2% and 0.38%, respectively, over 3 h. The experimental results agree with the simulation results and both prove that the PZ fiber front end can successfully suppress the FM-to-AM conversion. The PZ fiber front end is a promising alternative for improving the performance of the front end in high-power laser facilities. (C) 2016 Optical Society of Americ
Thermal-induced wavefront aberration in sapphire-cooled Nd:glass slab
No full textFrontend Group of National Laboratory on High Power Laser and Physics in Shanghai Institute of Optics and Fine MechanicsWe demonstrate for the first time a sapphire-cooled Nd: glass composite assembly based on optical bonding of two thin sapphire plates to a Nd: glass slab for efficient heat removal. The distributions of temperature, stress, depolarization loss, and wavefront aberration were obtained by finite element analysis. The simulation results were verified experimentally. Although the heat generation rate was 4.5 W/cm(3), the temperature increase was within 5.7 degrees C at the center of the sapphire surface, and the whole wavefront aberration was 1.21 lambda (lambda = 1053 nm). This demonstration opens up a viable path toward novel repetition rate Nd: glass laser amplifier designs with efficient double-sided room-temperature heat sinking on both sides of the slab
Total internal reflection orders in transmission grating
No full text当前高功率激光装置系统中, 国内使用透射式衍射光栅进行光束采样, 国外甚至使用光栅聚焦并同时结合谐波分离和采样功能. 高功率激光辐照下, 除了0级透射打靶光以及目标取样光外, 其他级次衍射光的影响也不可忽视, 可能造成诸如鬼像聚焦破坏、时间脉宽测量不稳定、近远场测量噪声等问题. 尤其是透射衍射光栅内部全反射级次会导致光栅出射一系列规律的衍射花样, 造成上述干扰和危害. 首先理论上针对透射式光栅(包括取样光栅和聚焦光栅)进行了相应的计算和分析, 然后从实验上观察并测量了取样光栅内部全反射级次的现象, 并且结Major Project of the National Science and Technology of the Ministry of Science and Technology of China [GFZX0205010405.2]; Young Scientists Fund of the National Natural Science Foundation of China [11204331]In a current high-power laser system, transmission grating has been used to sample, separate and focus laser beam. Under high power laser irradiation, besides the 0-order shooting beam and target sampling beam, the detrimental influence of other diffraction orders should be taken into consideration seriously. These useless orders may damage other nearby optical elements and mechanical devices, disturb and confuse the measurement of time pulse and near/far-field intensity. Especially the total internal diffraction order will lead to some series diffraction patterns, causing the above problems. First, relevant theoretical calculation and analysis are carried out for transmission grating (including beam sample grating and focusing grating), which can predict and indicate these inconspicuous diffraction orders. These orders appear on four receiving screens regularly and periodically, and the periodic distance between them is determined by ray-tracing draft. Second, the phenomenon of total internal reflection order is observed and measured by combining with anti-reflection film. The measured periodic spacings on three screens are 24 mm, 26 mm and 35 mm, respectively. Moreover, energy intensities of these redundant orders are measured finely, which shows that their contrasts or SNRs to 0-order main laser is in a range of 10(-8)-10(-4)). Finally, some appropriate and effective approaches to eliminating or avoiding total internal reflection and other useless orders are proposed and discussed, which include 1) coating by anti-reflection film with pre-deep etching; 2) optimizing the grating design to make redundant orders far from target spot; 3) placing laser scattering or absorbing devices at corresponding position to avoid being damaged by the side-leakage energy and ghost image of total internal reflection and other redundant orders
1.31 and 1.32 mu m dual-wavelength Nd:LuLiF4 laser
No full textNatural Science Foundation of Shandong Province, China [ZR2013FM027]; National Science Foundation for Distinguished Young Scholars of China [61308020]; Independent Innovation Foundation of Shandong University, IIFSDU [2082014TB011]We demonstrate the operation of Nd:LuLiF4 laser with efficient 1.31 and 1.32 mu m dual-wavelength. Maximum continuous-wave output power of 1.63 W is obtained at an incident pump power of 9.97 W and 8% transmission of output coupler (OC), giving a slope efficiency of 17.9%. When monolayer graphene is employed as saturable absorber, stable passively Q-switched 1.31 and 1.32 mu m dual-wavelength laser operation still remains. The maximum average output power of 1.33 W, the largest pulse energy of 17.3 mu J and the highest peak power of 111.6 W are achieved with the 8% OC. Meanwhile, the shortest pulse duration of 133 ns and the highest repetition rate of 91 kHz are rendered by the 3.8% OC cavity. (C) 2016 Elsevier Ltd. All rights reserved
A novel blue-emitting KCa4(BO3)(3):Ce3+ phosphor for white LED application
No full textNational Natural Science Foundation of China [51302283]; Natural Science Foundation of Shanghai [13ZR1463400]; Innovation Program of Shanghai Municipal Education Commission [15ZZ093]A blue-emitting phosphor KCa4(BO3)(3) doped with Ce3+ was prepared by solid state reaction. Its phase purity and synthesis temperature were investigated by powder X-ray diffraction (XRD). The optical properties were studied by photoluminescence (PL) and photoluminescence excitation (PLE) spectra. In addition, the temperature-dependent PL measurement was also carried out. The phosphor showed a broad and strong blue emission centered at 428 nm under near ultraviolet light excitation at 370 nm. Ce3+ ions in the three Ca sites of the host showed the similar centroid shift (epsilon(c)) and crystal field splitting (epsilon(cfs)). The quantum efficiency of the phosphor with optimal doping concentration was 68% of that of commercial blue phosphor BaMgAl10O17:Eu2+. It indicated the promising applicability as a blue-emitting phosphor for UV-converting white light-emitting diodes