钠乙烷准分子产生钠D_2线荧光寿命的实验研究

准分子宽带抽运钠金属激光器具有实现钠信标光源的潜质,该激光器在运转过程中需要借助准分子将钠原子由基态转换为激发态,因此有必要对由准分子解离产生的钠原子激发态荧光寿命开展实验研究。采用不同波长的蓝翼抽运光对不同温度的钠乙烷准分子体系进行激发,分别测量钠D_1线和钠D_2线的荧光寿命。结果表明,3~2P_(3/2)与3~2P_(1/2)能级的荧光寿命明显长于其自然寿命,且激发波长越长,荧光寿命延长得越明显。辐射捕获效应是导致荧光寿命延长的另一个因素。随着泵浦单光子能量下降,钠乙烷准分子被激发到A~2Π_(3/2)态的概率变大,能够长时间产生激发态钠原子,这也会使荧光寿命延长。与钠D_1线相比,钠乙烷准分子体系钠D_2线的放大自发辐射信号的可放大性更好。更好的可放大性以及较长的荧光寿命使得钠D_2线激光更易于实现。     

铅蒸气激光器

我们利用实验室里现有的进行铜蒸气激光实验的装置,进行了Au、Ba、Pb等蒸气激光器的实验。本文主要报告Pb蒸气激光器(7229(?)波长)的实验结果。 铅原子的基态是6p~2(3p),上激光能级是第一共振能级6s~26P7s(~3p_1~0),7229(?)波长的下激光能级是6S~26p~2(~1D_2),有关能级图见图10但是,激光跃迁~3p_1~0→~1D_2是三重态到单重态的跃迁,在L-S耦     

用辐射法研究CuⅡ激光振荡的增益特性

在自制的全金属铜空心阴极激光器中得到了GuⅡ740.4nm(6S~3D_3-5P~3P_2~0)谱线的激光振荡。为研究激光运行的最佳条件,我们用辐射法测量了不同激发条件下GuⅡ740.4nm谱线的增益特性。根据测量的结果,可以得到如下结论:     

强磁场下金属钠蒸气中二次谐波性质的研究

金属蒸气由于具有中心对称性,故在电偶极矩近似下,二次谐波是不存在的或者说是极弱的.近几年来陆续出现了一些金属蒸气中二次谐波的报道.首先是在1977年Matsuoka报道了在横向直流磁场70高斯下钠蒸气4~2D-3~2S的二次谐波.实验是用闪光灯泵浦染料激光器调谐到该跃迁的双光子共振上.1983年Chen报道了在无外磁场下观察到钠蒸气中同一跃迁的二次谐波,并且确认了地磁场的作用.1981年Freeman报道了无外磁场下钠蒸气的二次谐波的存在,并提出了由多光子电离的电场所致.但是我们认为磁场的作用是主要的,在强磁场下二次谐波的强度是否仍然与磁场强度平方成正比,这个问题至今未见报道.我们研究     

由Na_2-Na双光子混合共振和四波混频产生的可调谐紫外相干辐射

由与Na_2-Na双光子混合共振相关联的四波混频过程产生可调谐紫外相干辐射。当以614.5～617.4nm的染料激光泵浦钠蒸气时,第一个光子将钠分子从基态X_1∑_g~+激发到A~1∑_u~+态;通过Na_2~*-Na近共振碰撞能量转移过程,将处于基态3S的钾原子激发到3P(3/2),(3/2)态;第二个光子将钠原子共振激发到5S态,从而产生5S→4P的受激辐射和4P→4S的串级受激辐射。而在离共振激发时,除上述受激辐射(或串级受激辐射)外,还存在分别起始于3P_(1/2)和3P(3/2)态的受激喇曼散射。上述受激辐射(或串级受激辐射)和受激喇曼散射分别与泵浦光的     

钠蒸气参量四波混频紫外辐射的产生

记录并分析了钠原子蒸气形成近４Ｄ能级双光子共振参量四波混频产生的３３０ｎｍ信号，描述了信号强度随实验条件变化的规律，确定了最强辐射条件。     

碲红外滤光片

用各种滤光片能滤出红外器件和系统的一定红外光谱区。作者认为,以碲作滤光片有一系列优点。实验中所用的碲系六角系结晶,它的C轴垂直于顶部Te原子六角体平面。该晶体常被视作三角系,并表明为D_3点状和D_3~4或D_3~6空间对称群。资料[2-4]对碲的光学特性作了极为详尽的研究。研究结果表明,碲的本征吸收无论是(?)或(?)都取决于直接转换((?):极化红外辐射的电矢量)。200～     

基于钠原子3S-4S跃迁受激电子Raman散射的可调谐红外输出

用准分子激光器泵浦的染料激光器激励钠蒸气,当染料激光输出波长在334.0～338.8nm范围内调谐时,观测到2.38～2.65μm的红外强辐射,具有明显的阈值,谱线窄,发散角小。从理论计算和实验数据判明,该辐射属于钠原子3S-4S跃迁的SERS过程。光子转换效率可达30％。当泵浦光超过阈值后,SERS强度随泵浦功率的提高而大大增强,与理论的指     

Rb(7~2D)-N_2碰撞FST截面的测量

使用Rb灯和CW染料激光器选择两步激发基态钕原子集居于“中间”激发态7D_(5/2)或者7~2D_(3/2)能级,产生的原子荧光包括碰撞集居态的敏化荧光I_(3/2)~1和光激发态的直接荧光I_(3/2)~2。测量两个荧光成份的相对强度比I_(3/2)~1/I_(3/2)~2与N_2分子气体压力的关系,得到截面σ_(fs)~*、σ_(fs)~*′和σ_(tr)~*实验值。本文对实验结果进行了分析与讨论。     

利用锌蒸气二次谐波产生140nm相干光

在锌蒸气中,利用双光子共振增强,产生了自6~1S_0、6~1D_2的相干二次谐波151.4nm、140.7nm,我们发现缓冲气体氩的气压对倍频输出有很重要的影响。     

Electron Field Emission of Geometrically Modulated Monolayer Semiconductors

Electron field emission, electrons emitted from solid surfaces under high electric field, offers significant scientific interests in materials sciences and potential optoelectronics applications. 2D atomic layers, such as MoS₂, exhibit fascinating properties for diverse applications in next‐generation nanodevices and rich physical phenomena for fundamental research. However, the study on field emission of semiconducting monolayers is lacking owing to its low efficiency and stability of electron emission. Here, electron field emission of the geometrically modulated monolayer semiconductors suspended with 1D nanoarrays is demonstrated. Chemical vapor deposition synthesis of two prototype monolayers of transition metal dichalcogenides (TMD), MoS₂ and MoSe₂, is presented and their diverse band structures offer an ideal platform to explore the fundamental process of the electron emission in the TMD. Geometrical modulation and charge transfer of the semiconducting monolayers can be significantly tuned with the structural suspension with the 1D ZnO nanoarrays. Possible mechanisms on the enhanced electron emission of the 2D monolayers are discussed. With geometrical control of the monolayers, a highly efficient and stable electron emission of TMD monolayers is achieved in low turn‐on electric fields, enabling applications on electrons sources and opening a new avenue toward geometrically tuned atomic layers.     

钠蒸气近4D能级双光子共振光谱分析

由钠蒸气近4D能级双光子共振光谱证实，存在330nm纯参量四波混频信号，共振时参量四波混频抑制了放大的自发辐射，而激光波长失谐时产生的受激超拉曼散射削弱了参量四波混频。     

Synthesis of GaN nanowires and nanorods via self-growth mode control

The synthesis of hexagonal wurzite one-dimensional (1D) GaN nanostructures on c-Al₂O₃ substrates was investigated using a thermal chemical vapor deposition (CVD) process. The diameter of the GaN nanostructures was controlled by varying the growth time using a mixture of GaN powder and Ga metal with the ammonia gas reaction. The morphologies of the GaN nanowires and nanorods were confirmed by field emission scanning electron microscopy. The micro-Raman spectroscopy and X-ray scattering measurements indicated that the GaN nanostructures had a hexagonal wurzite structure without any oxide phases. We investigated the difference in the structural properties between the GaN nanowires and nanorods. Deep-level emission bands were not observed in cathodoluminescence measurements from either the GaN nanowires or nanorods, indicating the incorporation of low-level impurities into our 1D GaN nanostructures.     

Recent Advances in 2D Rare Earth Materials

2D rare earth (RE) materials have received considerable attention in recent years due to the fascinating luminescence, magnetism, and electric properties originated from RE associated with sharp and various emission peaks, intrinsic 2D ferromagnetism, and incommensurate charge density wave. These materials might open up a new prospect in next-generation lighting, magnetic devices, and phototransistors. Herein, a comprehensive review of 2D RE materials is presented, focusing on their recent progresses. First, the crystal structures of 2D RE materials are discussed. Then, typical synthesis methods such as mechanical exfoliation, molecular beam epitaxy, pulsed laser deposition, and chemical vapor deposition are introduced. Furthermore, various properties in luminescence, magnetism, and electronics are summarized. The recently reported RE-based 2D novel photodetectors are outlined as three constructions: MoS₂/RE, graphene/RE, and perovskite/RE, which show promising applications for both narrow and broad band detection arised from the special absorption windows of different RE elements. Finally, the conclusions and outlook of this area are proposed, such as exploring novel 2D RE compounds, improving stability, and broadening applications.     

Characterization of quaternary AlInGaN epilayers and polarization-reduced InGaN/AlInGaN MQW grown by MOCVD

We have demonstrated the growth of quaternary AIlnGaN compounds at different growth temperatures and pressures with metalorganic chemical vapor deposition (MOCVD). The optical properties of the samples have been investigated by photoluminescence (PL) at different temperatures. The results show that the sample grown at higher temperature (850℃) exhibits the best optical quality for its sharp band edge luminescence and weak yellow luminescence. The AlInGaN exhibited three-dimensional (3D) growth mode at higher pressure. The band edge emission almost disappeared. With the optimization of AlInGaN growth parameters, we replaced the traditional barrier in InGaN/GaN multiple quantum wells (MQWs) with AlInGaN barriers. The peak wavelength for the InGaN/AlInGaN-MQW based light emitting diodes (LEDs) was very stable at various injection current levels because of the polarization-matched InGaN/AlInGaN MQWs.     

Enhanced electron emission from phosphorus-doped diamond-cladsilicon field emitter arrays

Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities     

Centimeter‐Scale and Visible Wavelength Monolayer Light‐Emitting Devices

Monolayer 2D transition metal dichalcogenides (TMDCs) have shown great promise for optoelectronic applications due to their direct bandgaps and unique physical properties. In particular, they can possess photoluminescence quantum yields (PL QY) approaching unity at the ultimate thickness limit, making their application in light‐emitting devices highly promising. Here, large‐area WS₂ grown via chemical vapor deposition is synthesized and characterized for visible (red) light‐emitting devices. Detail optical characterization of the synthesized films is performed, which show peak PL QY as high as 12%. Electrically pumped emission from the synthetic WS₂ is achieved utilizing a transient‐mode electroluminescence device structure, which consists of a single metal–semiconductor contact and alternating gate fields to achieve bipolar emission. Utilizing this aforementioned structure, a centimeter‐scale ( ≈ 0.5 cm²) visible (640 nm) display is demonstrated, fabricated using TMDCs to showcase the potential of this material system for display applications.     

浸泡Ni(NO3)2溶液的石墨在不同温度下生长的碳纳米管及其场发射性能

将石墨衬底浸泡于0.5mol/LNi(NO3)2溶液中一段时间,之后利用低压化学气相沉积法在不同温度的条件下生长碳纳米管薄膜。研究了碳纳米管的生长温度对其场发射性能的影响。通过扫描电子显微镜和拉曼光谱对生长的碳纳米管薄膜的表征发现,随着碳纳米管的生长温度的增加,碳纳米管的直径与相应拉曼光谱中的G峰和D峰(ID/IG)的峰强比减小。同样,碳纳米管的G峰的半峰宽随着碳纳米管的生长温度的增加而减小,这表明碳纳米管的石墨化程度的增强。实验中发现,碳纳米管的场发射性能依赖于碳纳米管的生长温度。     

Silicon carbide technology for blue-emitting diodes

Silicon carbide light-emitting diodes with emission in the blue range of the spectrum have been produced by vapor growth and liquid-phase epitaxy. The technology of devices with a p-type (Al-doped) luminescent layer is described. Emission spectra and efficiency data are presented for two types of diodes.     

Effect of diamond-like carbon coating on the emissioncharacteristics of molybdenum field emitter arrays

We have studied the electron emission characteristics of Mo field emitter arrays (FEAs) using a diamond-like carbon (DLC) film deposited by a layer-by-layer technique using plasma enhanced chemical vapor deposition. The turn-on voltage was lowered from 55 to 30 V by a 20 nm thick hydrogen-free DLC coating and maximum emission current was increased from 166 to 831 μA. Also the gate voltage required to get the anode current of 0.1 (μA/emitter) decreases from 77 to 48 V. Furthermore, the emission current from DLC coated Mo FEAs is more stable than that of noncoated Mo FEAs