猝发双脉冲直线感应加速器组元研究

 在原单脉冲直线感应加速器（LIA）组元的基础上，利用电缆延时和电缆反射两种方式获得了间隔500～1 000 ns的猝发双脉冲输出。在感应加速腔上进行了双脉冲实验，获得了幅度大于200 kV、前沿小于35 ns、平顶大于60 ns的双脉冲加速电压波形。两种方式中第一个脉冲的前沿和幅度都达到了原单脉冲组元的水平，表明加速腔负载的变化对波形没有明显影响，但由于电缆对波形的损耗，第二个脉冲的幅度和前沿比第一个脉冲略差。可以利用水介质传输线来代替长电缆，减小传输线的长度及其对波形的损耗。两个脉冲间的幅度差异可以通过改变长电缆的阻抗来调节。实验表明，通过这两种猝发双脉冲的产生方式并结合加速腔磁芯的改进，可简单高效地完成原单脉冲LIA的双脉冲改造。     

猝发双脉冲直线感应加速器组元研究

直线感应加速器（LIA）是产生强流、高能电子束的重要装置之一。现有的直线感应加速器均以单次方式工作，加压一次只能加速一个束流脉冲打靶，而实际应用常希望其能工作在高重复频率的猝发多脉冲模式下。对原单脉冲LIA进行猝发双脉冲改造，无疑是获得多脉冲LIA最经济最简单的方法。     

磁芯材料脉冲间叠加复位研究

 介绍了通过反向叠加长脉冲的方法，在双脉冲间隔小于1 μs的情况下对直线感应加速器磁芯进行的脉冲间复位实验，复位后波形幅度得到了明显改善，在最大伏秒值280 kV×100 ns的单脉冲感应腔上得到了两个伏秒值为200 kV×100 ns的感应脉冲。实验表明：当主脉冲脉宽小于100 ns，间隔大于500 ns时，采用脉冲间叠加复位的方法,将主脉冲叠加在一个反向的长脉冲上（脉宽大于10 μs，最大幅度约为主脉冲的20%）形成正负脉冲串，能有效提高感应加速腔磁芯的利用率，且对感应主脉冲没有明显影响，使单脉冲直线感应加速器的多脉冲改造成为可能。     

直线感应加速器组元的双脉冲改造

 对用于单脉冲直线感应加速器的加速组元进行了双脉冲改造的初步尝试：利用传输线延时获得了双脉冲馈入；用铁氧体作为磁芯材料，在感应腔上得到了双脉冲腔压波形。结果表明，现有组元功率系统经过简单的改造，可以获得两个甚至多个脉冲输出；在伏秒值允许的范围内，铁氧体磁芯的感应腔可以感应出双脉冲波形。为以后多脉冲直线感应加速器的改造和设计提供了一个方向，也提出了一些有待解决的问题。     

国产非晶磁芯应用于感应加速组元的可行性研究

介绍了国产非晶合金应用于感应加速组元的可行性研究的初步结果. 采用国产1K101型铁基非晶合金(FeSiB)~带材, 研制了非晶磁芯, 并利用加速腔(或实验腔)对研制的非晶磁芯的磁性能、绝缘性能和稳定性等方面进行了研究. 高压单脉冲实验可获得脉冲幅度为240kV、脉冲前沿为17ns(10%—90%)、脉冲平顶为72ns(±1%)的单脉冲; 高压猝发三脉冲实验可获得前沿35ns、脉冲平顶60ns的三脉冲, 磁芯的有效平均磁密跳变为1.41T. 耐压实验研究中, 得到了电压幅值为282kV的三脉冲. 非晶磁芯的性能稳定, 满足感应加速组元对磁芯性能的要求.     

国产非晶磁芯应用于感应加速组元的可行性研究

介绍了国产非晶合金应用于感应加速组元的可行性研究的初步结果.采用国产1K101型铁基非晶合金(FeSiB)带材,研制了非晶磁芯,并利用加速腔(或实验腔)对研制的非晶磁芯的磁性能、绝缘性能和稳定性等方面进行了研究.高压单脉冲实验可获得脉冲幅度为240kV、脉冲前沿为17璐(10%-90%)、脉冲平顶为72ns(±1%)的单脉冲;高压猝发三脉冲实验可获得前沿35ns、脉冲平顶60ns的三脉冲,磁芯的有效平均磁密跳变为1.41T.耐压实验研究中,得到了电压幅值为282kV的三脉冲.非晶磁芯的性能稳定,满足感应加速组元对磁芯性能的要求.     

高重复率猝发高压多脉冲加速组元

详细介绍了基于形成线并联和传输线延时两种不同技术路线的MHz重复率猝发多脉冲加速组元的工作原理、应用背景和技术特点,针对现有传输线延时双脉冲加速组元的主要问题提出了一种新的猝发高压双脉冲加速组元设计思路并进行了实验验证,使双脉冲加速组元在兼顾更高稳定性和更好波形品质的同时,解决了双脉冲电压独立调节、间隔调节及单双脉冲模式转换的问题。     

低压重频感应加速组元参数分析

针对脉冲源+传输线+感应腔和储能电容+固态开关+感应腔两种常见的脉冲感应组元结构,对相同感应腔的腔压波形进行了实验对比和理论分析,推导出了不同组元结构下感应腔中磁芯回路电感量、匹配电阻阻值和感应脉冲幅度间的关系表达式,分析对比了两种组元结构下感应腔电感量和电阻值变化对腔压平顶影响的程度和差异,为低压重频脉冲感应加速组元的参数选择和优化提出建议和判据。     

MHz重复频率脉冲功率技术

采用串联单传输线、并联Blumlein脉冲形成线和高重复频率固体开关等技术路线开展了MHz重复频率脉冲功率技术研究。利用串联单传输线获得了幅度约200 kV,时间间隔约500 ns的双脉冲。利用并联使用的Blumlein系统和特殊设计的汇流/隔离网络获得了幅度约275 kV,时间间隔约500 ns的三脉冲。利用并联MOSFET和感应叠加原理研制了6 kV/2.5 MHz固体调制器。结果表明:3种方式均可以猝发MHz的方式输出高品质的高压脉冲串,可根据实际的需求选择合适技术路线。     

双脉冲电子直线感应加速器实验研究

 Mini-LIA为MHz重复频率双脉冲电子直线感应加速器,由双脉冲功率系统、热阴极电子枪注入器及金属玻璃磁芯感应加速腔等组成。在此平台的实验获得了数百ns间隔（即MHz重复频率）的双脉冲高压,每个脉冲幅值达到80 kV,脉冲半高全宽为80 ns;在感应腔加速间隙处测得双脉冲加速电场;在加速器出口处测量得到流强约1.1 A的双脉冲电子束流。实验结果表明：利用硅堆隔离汇流装置可实现MHz重复频率的双脉冲高压,金属玻璃磁芯感应加速腔和六硼化镧热阴极电子枪均适合MHz重复频率双脉冲工作方式。     

Graded index profiles and loss-induced single-mode characteristics in vertical-cavity surface-emitting lasers with petal-shape holey structure

The 850-nm oxide-confined vertical-cavity surface-emitting lasers with petal-shape holey structures are presented.An area-weighted average refractive index model is given to analyse their effective index profiles,and the graded index distribution in the holey region is demonstrated.The index step between the optical aperture and the holey region is obtained which is related merely to the etching depth.Four types of holey vertical-cavity surface-emitting lasers with different parameters are fabricated as well as the conventional oxide-confined vertical-cavity surface-emitting laser.Compared with the conventional oxide-confined vertical-cavity surface-emitting laser without etched holes,the holey vertical-cavity surface-emitting laser possesses an improved beam quality due to its graded index distribution,but has a lower output power,higher threshold current and lower slope efficiency.With the hole number increased,the holey vertical-cavity surface-emitting laser can realize the single-mode operation throughout the entire current range,and reduces the beam divergence further.The loss mechanism is used to explain the single-mode characteristic,and the reduced beam divergence is attributed to the shallow etching.High coupling efficiency of 86% to a multi-mode fibre is achieved for the single-mode device in the experiment.     

Improvement of performance characteristics of deep violet InGaN DQW lasers using a strip DQW active region

The effect of the laser ridge width on the performance characteristics of deep violet In_0.082Ga_0.918N/GaN double quantum well (DQW) laser diodes (LDs) has been numerically investigated. Simulation results indicated that threshold current of LDs is decreased and slope efficiency and differential quantum efficiency (DQE) are increased by decreasing ridge width, whereas output power is decreased. The results also showed that a decrease of more than 1 μm in the ridge width reduces the threshold current, whereas the slope efficiency, output power, and DQE are decreased. A new DQW LD structure with a strip active region has been proposed to obtain a lower current threshold and higher output power, slope efficiency, and DQE. The results showed the InGaN DQW LD with a strip DQW active region has the highest output power, slope efficiency, and DQE; it also has a lower threshold current compared with that of the original LD. The comparative study conducted for the LDs with output emission wavelengths of 390, 414 and 436 nm has also confirmed the enhancement in LD performance using the strip DQW active region structure.     

酸蚀深度对熔石英三倍频激光损伤阈值的影响

 采用干涉仪和台阶仪测试蚀刻深度随时间的变化,结合材料去除速率测量,研究了HF酸蚀液对熔石英表面蚀刻的影响。测试了蚀刻后损伤阈值和表面粗糙度的变化。研究表明,熔石英表面重沉积层厚度约16 nm,亚表面缺陷层大于106 nm;重沉积层去除后损伤阈值增大,随亚表面缺陷层暴露其阈值先降低后又增加,最后趋于稳定;然而,随蚀刻时间的增加,其表面粗糙度增大。分析表明,蚀刻到200 nm能有效地提高熔石英的低损伤阈值,有利于降低初始损伤点数量和提高熔石英表面的机械强度。     

808 nm大功率半导体激光器阵列的优化设计

 采用激射波长为808 nm的GaAs/AlGaAs梯度折射率波导分别限制单量子阱结构外延片,制备了沟道深度不同的半导体激光器阵列,并对载流子分布进行理论分析和模拟。理论和实验结果表明：引入脊形台面和隔离沟道后,激光器阵列的输出功率、电光转换效率、斜率效率和光谱特性均有显著提高。随着沟道的加深,对电流侧向扩散的限制作用增强,从而提高了阵列性能。     

K9基片的亚表面损伤探测及化学腐蚀处理技术研究

 研究了几种类型的腐蚀液对K9基片化学腐蚀的影响。通过腐蚀液对基片纵向腐蚀速度的变化初步判断了K9基片重沉积层的深度。考察了腐蚀前后基片表面参数的变化以及腐蚀对激光损伤阈值的影响。研究表明，特定的腐蚀液能够对K9基片进行平稳可控的腐蚀，并且腐蚀能提高其激光损伤阈值，其主要原因是去除了重沉积层及表面、亚表面缺陷中的污染物,但过多的腐蚀会暴露本来为重沉积层所掩盖的划痕等亚表面缺陷，所以腐蚀并非越深越好。同时，表面各种杂质与缺陷的去除能够提高材料的机械强度，从而也有利于提高材料的激光损伤阈值。     

紧凑型窄线宽分布反馈光纤激光器

 在铒/镱共掺杂有源光纤上直接刻蚀光栅,制成一台紧凑型非对称π相移分布反馈光纤激光器。光栅总长度约50 mm,最佳相移位置在29 mm处,最佳耦合系数为150 m^-1。采用980 nm激光二极管同向泵浦,当最大泵浦功率为200 mW时,在1 550.94 nm处实现约10 mW激光输出,线宽小于0.05 nm,阈值约35 mW,斜率效率为6.06%,总光 光转换效率为5%,基本满足长距离光通信系统光源功率实用化的要求。     

940nm垂直腔面发射激光器的设计及制备

利用PICS3D计算得到InGaAs/GaAsP应变补偿量子阱的增益特性,得到量子阱的各项参数,再通过传输矩阵理论和TFCalc膜系设计软件分别仿真出上下分布式布拉格反射镜的白光反射谱.采用金属有机化合物气相沉积技术外延生长了垂直腔面发射激光器结构,之后通过干法刻蚀、湿法氧化以及金属电极等芯片技术制备得到8μm氧化孔径的VCSEL芯片.最终,测试得到其光电特性实现室温下阈值电流和斜效率分别为0.95 mA和0.96 W/A,在6 mA电流和2 V电压下输出功率达到4.75 mW,并测试了VCSEL的高温特性.     

Theoretical and Experimental Investigations of Diode-Pumped Tm:YAG Laser in Active Mirror Configuration

Based on the rate-equations of quasi-three-level lasers, we analyzed the threshold and the output power of longitudinally pumped Tm:YAG lasers in an active mirror configuration. In contrast to one-pass pumping, two-pass pumping in this configuration will result in a 24% decrease in threshold and 16% increase in slope efficiency. Using a 3-W diode-laser pumping in the active mirror configuration, we demonstrated a CW Tm:YAG laser and obtained 735 mW output power with a slope efficiency up to 49%. Using a Ti:sapphire laser to pump the same device, the threshold power was further reduced and the slope efficiency reached 59%.     

Highly confined and continuous single-mode operation of self-align photonic crystal oxide VCSEL

In this letter, we report on single-mode operation of originally multi-mode oxide VCSEL by using etched photonic crystal air holes and unique trench structure. The device fabrication utilized conventional photolithography; with simplified lithography step of self-aligning the photonic crystal and trench structures to the laser aperture for efficient and vigorous device processing. The fabricated photonic crystal VCSEL with trench device exhibits a single-mode output power of 0.7 mW, threshold current of 3.5 mA, slope efficiency of 0.10 W/A, and continuous single-mode output spectra at wide operating current range. The results are compared with conventional multi-mode oxide VCSEL of similar device geometry. In addition, theoretical analysis is presented for developing further understanding of the photonic crystal VCSEL.     

Optimization of inductively coupled plasma deep etching of GaN and etching damage analysis

Inductively coupled plasma (ICP) etching of GaN with an etching depth up to 4 μm is systemically studied by varying ICP power, RF power and chamber pressure, respectively, which results in etch rates ranging from ∼370 nm/min to 900 nm/min. The surface morphology and damages of the etched surface are characterized by optical microscope, scanning electron microscope, atomic force microscopy, cathodoluminescence mapping and photoluminescence (PL) spectroscopy. Sub-micrometer-scale hexagonal pits and pillars originating from part of the structural defects within the original GaN layer are observed on the etched surface. The density of these surface features varies with etching conditions. Considerable reduction of PL band-edge emission from the etched GaN surface indicates that high-density non-radiative recombination centers are created by ICP etching. The density of these non-radiative recombination centers is found largely dependent on the degree of physical bombardments, which is a strong function of the RF power applied. Finally, a low-surface-damage etch recipe with high ICP power, low RF power, high chamber pressure is suggested.