一种微波源驱动的超导HEB太赫兹直接检测器北大核心CSCD

本文介绍了一种基于超导氮化铌(NbN)热电子测辐射热计(HEB)的太赫兹(THz)直接检测器,创新性地采用易调控的微波驱动方法,使其偏置在最佳工作点,得到了在4.2K的工作温度下、0.65THz频点的噪声等效功率(NEP)为1.6pW/Hz^(1/2).相比传统加热驱动的方法,微波驱动更易调控,有利于构建阵列读出电路,还可减少功耗等.由于该检测器响应速度快、灵敏度高的特点,有望应用于快速THz成像和脉冲信号检测等系统.     

一种微波源驱动的超导HEB太赫兹直接检测器

本文介绍了一种基于超导氮化铌(NbN)热电子测辐射热计(HEB)的太赫兹(THz)直接检测器,创新性地采用易调控的微波驱动方法,使其偏置在最佳工作点,得到了在4.2K的工作温度下、0.65THz频点的噪声等效功率(NEP)为1.6pW/Hz~(1/2).相比传统加热驱动的方法,微波驱动更易调控,有利于构建阵列读出电路,还可减少功耗等.由于该检测器响应速度快、灵敏度高的特点,有望应用于快速THz成像和脉冲信号检测等系统.     

基于超导HEB的太赫兹脉冲信号检测

本文利用超导氮化铌(NbN)热电子测辐射热计(HEB)结合自行开发的傅里叶变换光谱仪(FTS)来实现太赫兹(THz)脉冲信号的快速直接检测.该检测器采用易调控的微波来驱动超导NbNHEB芯片,使其偏置在直接检测的最佳工作点(测得的噪声等效功率为:8×10~(-12)W/(Hz)~(1/2)).通过与用同样灵敏度的商用低温半导体测辐射热计(Bolometer)测量到的THz量子级联激光器(QCL)辐射谱的结果进行比较,表明我们初步构建的基于超导NbNHEB直接检测器的系统已具有与商用Bolometer检测器同等的性能.     

自差分交流偏置超导纳米线单光子探测器

超导纳米线单光子探测器(SNSPD)因其优异的综合性能,在量子信息、激光雷达等方面有广泛的应用.通常, SNSPD工作在直流偏置下,在时域上具有自由运行探测的优点.而在卫星激光测距、单光子激光雷达等光信号到达时间有规律的应用场景中,使用交流偏置有望提升器件运行速率、有效抑制背景暗计数,却存在信号读出困难的棘手问题.本文报道了自差分读出的交流偏置SNSPD系统,该系统包含两根并行排布纳米线构成的2-pixel SNSPD器件.给两根纳米线加载相同的100 MHz交流偏置信号,并对两路输出信号差分使噪声信号相抵消,实现光子响应信号的读出.基于该方法测得,响应信号的信噪比相比差分之前提升10倍,在交流偏置下器件的暗计数降低至直流偏置下的约1/4,计数率达到直流偏置下的约1.5倍.本文为交流偏置SNSPD测试提供了一种思路,为其应用提供参考数据.     

HEB太赫兹混频器使用微波补偿的稳定方法

我们对氮化铌(NbN)热电子测热辐射计(Hot Electron Bolometer,简称:HEB)的太赫兹(Terahertz,简称:THz)混频器的稳定性进行了研究,并探讨了相应的简易稳定方法.我们测量了HEB THz混频器在4.2K温度下使用0.65THz本振源(Local Oscillator,简称:LO)的中频输出.为了稳定混频器的工作点,我们采用了一个具有微波补偿功能的反馈回路.在这个反馈回路里,我们使用的微波补偿频率(10GHz)远远低于NbN HEB混频器的工作频率(0.65THz),以补偿混频器的THz LO功率波动.这使系统的艾伦时间(Allan time)增加到22s以上,从而改善了系统的稳定性.     

基于VO2薄膜非致冷红外探测器光电响应研究

VO₂薄膜是非致冷微测辐射热红外探测器热敏电阻材料.研究中应用微电子工艺制备了VO₂溅射薄膜红外探测器,在296K的环境中测试了该探测器在不同的直流偏置、光调制频率下对873K标准黑体源8—12μm红外辐射的光电响应以及器件的噪声电压,在10和30Hz的调制频率下其响应率分别大于17kV/W和接近10kV/W.该探测器实现了探测率D大于1.0×10⁸cm (Hz)^1/2/W,热时间常量为0.011s的8—12μm非致冷 关键词： 非致冷测辐射热探测器 红外探测器 二氧化钒 薄膜     

高速、低噪声超导HEB太赫兹检测系统

本文介绍了一款高速、低噪声超导热电子测辐射热计(hot electron bolometer,HEB)的太赫兹检测系统,实验结果显示其有效提高了中频带宽(7.4GHz),减小了噪声温度(@0.65THz,系统在最佳偏置点的双边带(DSB)噪声温度为1185K).同时,用此款超导HEB太赫兹检测系统验证了改进后的傅里叶变换光谱仪(FTS)系统的稳定性及可靠性.     

基于VO_2薄膜非致冷红外探测器光电响应研究

VO2 薄膜是非致冷微测辐射热红外探测器热敏电阻材料 .研究中应用微电子工艺制备了VO2 溅射薄膜红外探测器 ,在 2 96K的环境中测试了该探测器在不同的直流偏置、光调制频率下对 873K标准黑体源 8— 12 μm红外辐射的光电响应以及器件的噪声电压 ,在 10和 30Hz的调制频率下其响应率分别大于 17kV/W和接近 10kV/W .该探测器实现了探测率D 大于 1 0× 10 8cmHz/W ,热时间常量为 0 0 11s的 8— 12 μm非致冷红外探测     

基于Pt/GaN/AlGaN异质结高响应度双波段紫外探测器

提出一种在AlGaN基PIN器件的p-GaN表面上沉积Pt,形成肖特基势垒(SB)-PIN异质结器件,器件的能带和载流子的输运发生了变化,这种新型光电探测器实现了双波段紫外探测,可分别工作在光伏和光电导模式下。器件在275 nm波长的紫外光照射的负偏置电压下,工作模式为光伏探测,当入射光功率密度为100μW/cm²,偏置电压为-10 V时,器件得到最大响应度(0.12 A/W);当偏置电压为-0.5 V时,器件得到最大探测率(1.0×10¹³ cm·Hz^1/2·W^-1)。器件在正偏置电压工作模式下可作为高响应、高增益的光电导探测器,当偏置电压为+10 V时,用275 nm和365 nm波长的紫外光照射(光功率密度为100μW/cm²),器件的响应度分别为10 A/W和14 A/W,外量子效率分别为4500%和4890%。所设计的双波段多功能器件将极大地扩展基于AlGaN的紫外探测器的用途。     

High repetition rate picosecond LiNbO_3 THz parametric amplifier and parametric gain

A high repetition rate, picosecond terahertz(THz) parametric amplifier with a LiNbO_3(LN) crystal has been demonstrated in this work. At a 10 k Hz repetition rate, a peak power of 200 W and an average power of 12 μW have been obtained over a wide range of around 2 THz; at a 100 k Hz repetition rate, a maximum peak power of 18 W and an average power of 10.8 μW have been obtained. The parametric gain of the LN crystal was also investigated, and a modified Schwarz–Maier model was introduced to interpret the experimental results.     

Co-Ni/FeMn双层膜中磁化强度对交换偏置的影响

固定CoNiFeMn双层膜中反铁磁层的厚度,改变CoNi铁磁层的成分来调节磁化强度,从而研究铁磁层的饱和磁化强度对CoNiFeMn双层膜中交换偏置的影响.研究表明,CoNiFeMn界面的交换耦合能U不是一个常量,而是随(MFM)12的增加而线性增加.其原因是铁磁层磁矩通过界面相互作用在反铁磁层中形成的局域交换磁场,在磁场冷却时影响反铁磁层的自旋结构或磁畴结构及双层膜中的交换偏置 关键词： 交换偏置 磁化强度     

Poloidal Structure of the Turbulence and the Turbulent Flux During Edge Plasma Biasing in the Castor Tokamak

The poloidal structure of the turbulence and the turbulent particle flux in the scrape-off layer (SOL) of the CASTOR tokamak are analysed by means of a poloidal ring of 124 probes distributed uniformly along the whole poloidal circumference. Fluctuation measurements are performed in standard ohmic regime as well as in discharges when a biased electrode is inserted either into the SOL or deeper into the confinement region. It is found that in both cases a strongly sheared radial electric field is created in the SOL, which de-correlates the density and radial velocity fluctuations and reduces their levels. Consequently, the turbulent flux is reduced. However, no phase shift is observed between density and radial velocity fluctuations. When the electrode is localized in the confinement region, all the above effects are less pronounced because of a smaller shear. In addition, the increase of the E × B velocity at biasing leads in both cases to the formation of oscillations in the temporal correlation function. These oscillations are specifically associated to the poloidal mode (m = q), which is created for a limited time and rotates poloidally. This mode does not modify the phase between density and radial velocity fluctuations and has no further effect on the turbulent flux.     

衬底偏置对ITO膜光学性质的影响

研究衬底偏置机理。在低温偏压衬底下,用三极反应溅射法镀制出在可见光区透射率为83％的ITO膜。测试低温负偏置衬底法与高温无偏置衬底法镀制ITO膜的光谱特性,发现两者在红外区有相似变化。确定出氧分压范围在(5～7)×10~(-3)Pa。     

Design and construction of hot limiter biasing system for the tokamak

A hot limiter biasing system with a simplified fast switch circuit was designed, constructed, and installed on the IR-T1 tokamak, and then the negative voltage applied to a hot limiter inserted inside the tokamak fixed limiter and the plasma current, poloidal, and radial components of the magnetic fields, loop voltage, diamagnetic flux, and the ion saturation currents in the absence and presence of the biased limiter were measured. Results of measurements of biasing effects on the plasma equilibrium behavior and edge plasma rotation are compared and discussed.     

The effect of the use of different electrode materials for edge-plasma biasing on plasma density and floating potential modifications

The effect of the use of different electrode materials for edge-plasma biasing on plasma density and floating-potential profile modifications has been recently investigated on the CASTOR tokamak. Dependences of biasing current, edge plasma density and floating potential on biasing voltage have been measured. Induced relaxation events and fast (10–50) kHz oscillations are shown and surface changes of the biasing electrodes are discussed in the paper. Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005.     

JMCT软件的自动源偏倚抽样功能及其应用

介绍JMCT（J Monte Carlo Transport）软件的多群中子伴随输运功能以及基于伴随通量的自动源偏倚抽样功能.对某商用压水堆屏蔽模型的模拟计算表明,采用自动源偏倚后,JMCT的模拟结果与实验值符合较好,比MCNP程序采用几何重要性方法的计算效率大幅提高.     

Transport and fluctuations during electrode biasing on TJ-II

Edge polarization experiments were carried out on TJ-II using an electrode. It has been found that the plasma response is different at densities below and above the threshold value to trigger the spontaneously development of E × B sheared flows. At low densities, the edge plasma potential is fully controlled by external biasing, while at higher densities it is determined not only by external biasing but also by the electric fields spontaneous developed. Although an improvement in particle confinement is observed for both polarities, a larger increase is observed for negative electrode bias. Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005.     

Efficiency of plasma biasing by movable localized limiter in tokamak ISTTOK

The correlation between the efficiency of plasma biasing and the position of a localized limiter has been investigated. It has been found that two distinct zones of limiter position can be distinguished in ISTTOK plasma: Far-zone at r _lim > 7.2 cm, and Close-zone at r _lim < 7.2 cm. The strongest modifications of edge plasma potential take place for both positive and negative limiter biasing when it is positioned inside Close-zone. The transition between zones is correlated with effective screening of the wall by the limiter, being more efficient as it is immersed deeper into the plasma. The indicative difference between zones can be a difference of non-ambipolar fluxes flowed onto short-circuited limiter: mostly positive (ion) inside Far-zone, and mostly negative (electron) inside Close-zone.Presented at the Workshop Electric Fields Structures and Relaxation in Edge Plasmas, Nice, France, October 26–27, 2004.     

Runaway electron generation decrease during a major disruption by limiter biasing in tokamaks

The high-energy current of runaway electrons during a major disruption in tokamak reactors can cause serious damage to the first wall of the reactors and reduce their life time. Therefore, finding a method to minimize runaway electron generation during a major disruption is much needed. Tokamak limiter biasing is one of the methods that can be used for controlling the radial electric field and can induce a transition to an improved confinement state. This paper attempts to examine the effect of limiter biasing on the generation of runaway electrons during a major disruption. To do so, a horizontal biased limiter placed on the tokamak was used. Main parameters such as plasma current, loop voltage, emitted hard X-ray intensity, magnetohydrodynamic (MHD) oscillation and H_α radiation and spectrum of hard X-rays, in the presence and absence of negative and positive limiter biasing, were measured. The results show that the application of limiter biasing during a major disruption can reduce runaway electron generation.     

Limiter Biasing Experiments on the Tokamak ISTTOK

The influence of the polarization of a localized limiter on the global and edge parameters is described. In particular, the effect of varying the limiter position and the bias voltage is investigated. Improvement in confinement has been obtained for both positive and negative limiter bias as a result of the creation of large radial electric fields in the region just inside the fixed limiter. Furthermore, it has been observed that the modification in the floating potential due to limiter biasing is proportional to the collected current.