ZnO薄膜的特殊光谱性质及其机理

以同步辐射真空紫外光(195nm)为激发源,在低温下观察到Si基衬底上ZnO薄膜的发光有三种紫外发射,其峰值波长分别为380,369．5,290nm。它们各自具有不同的衰减时间和不同的温度依赖关系,但其激发谱相同。强激发带不在近紫外区,而在真空紫外区(100～200nm),可能源于ZnO的下价带(Zn3d组态)电子的激发。对三种紫外发射的来源作了分析讨论。     

Monte Carlo方法模拟非直视紫外光散射覆盖范围

针对大气中紫外光散射通信的特点, 用Monte Carlo方法对紫外光非直视(NLOS) 通信三种工作方式的覆盖范围进行分析, 建立了基于Monte Carlo方法的NLOS紫外光传输模型.利用Monte Carlo模拟方法对三种NLOS散射方式的单次和多次散射路径损耗及覆盖范围进行模拟研究, 结果表明, 多次散射和单次散射的路径损耗基本一致, NLOS(a) 类全向发送全向接收通信方式覆盖范围最小但全方位性好, NLOS(b) 类定向发送全向接收通信方式的覆盖范围较大但有一定方向性, NLOS(c) 类定向发送定向接收通信方式的覆盖范围最大但有很强的方向性.     

利用ICCD定位宇宙线来测量探测器时间分辨的方法研究

本研究采用双层150 mm×150 mm闪烁条阵列定位宇宙线的入射和出射位置. 阵列信号光使用波移光纤吸收传输,在ICCD相机前插入前置像增强器,使信号光延迟大于200 ns, 使ICCD可以由外部高速触发信号控制,有效记录随机触发事例.该宇宙线定位系统可以同时多点密集测量 通用探测器测试平台的时间分辨和闪烁光的渡越时间.该新方法与传统时间分辨测量方法相比提高了30倍以上 的效率.实验结果显示:时间探测器的时间分辨好于200 ps,满足通用探测器测试平台的设计要求.     

The light-enhanced NO₂ sensing properties of porous silicon gas sensors at room temperature

The NO2 gas sensing behavior of porous silicon(PS) is studied at room temperature with and without ultraviolet(UV) light radiation.The PS layer is fabricated by electrochemical etching in an HF-based solution on a p +-type silicon substrate.Then,Pt electrodes are deposited on the surface of the PS to obtain the PS gas sensor.The NO2 sensing properties of the PS with different porosities are investigated under UV light radiation at room temperature.The measurement results show that the PS gas sensor has a much higher response sensitivity and faster response-recovery characteristics than NO2 under the illumination.The sensitivity of the PS sample with the largest porosity to 1 ppm NO2 is 9.9 with UV light radiation,while it is 2.4 without UV light radiation.We find that the ability to absorb UV light is enhanced with the increase in porosity.The PS sample with the highest porosity has a larger change than the other samples.Therefore,the effect of UV radiation on the NO2 sensing properties of PS is closely related to the porosity.     

近红外光诱导下NaYbF4:Tm3+,Eu3+ 体系中Eu3+的上转换发光

利用水热法制备得到NaYbF₄:0.01%Tm³⁺,20%Eu³⁺上转换材料,利用X射线衍射分析、扫描电子显微镜及光谱测试技术分别对其进行了结构、形貌以及光谱性质的表征。在980 nm近红外激光激发下,得到了Eu³⁺的可见到紫外范围的上转换荧光发射。分析表明:共掺杂NaYbF₄纳米材料中Tm³⁺到Eu³⁺离子的能量传递对布居Eu³⁺离子的激发态能级,获得Eu³⁺的上转换发光起着至关重要的作用。另外,在实验中首次获得了Eu³⁺对应于³P₀→⁷F_j (j=0,1,2)能级跃迁的上转换光发射。     

A tunable XUV monochromatic light source based on the time preserving grating selection of high-order harmonic generation

We accomplish a laboratory facility for producing a femtosecond XUV coherent monochromatic radiation with a broad tunable spectral range of 20 eV-75 eV. It is based on spectral selected single-order harmonics from intense laser driven high harmonic generation in gas phase. The time preserving for the selected harmonic radiation is achieved by a Czerny-Turner type monochromator designed with a conical diffraction grating mount for minimizing the time broadening caused by grating diffraction and keeping a relatively high diffraction efficiency. Our measurement shows that the photon flux of the 23-order harmonic(H23) centered at 35.7 eV is 1×10~9 photons/s approximately with a resolving power E/?E ≈ 36.This source provides an ultrashort tunable monochromatic XUV beam for ultrafast studies of electronic and structural dynamics in a large variety of matters.     

Improved performance of near UV light-emitting diodes with a composition-graded p-AlGaN irregular sawtooth electron-blocking layer

We investigate the performances of the near-ultraviolet(about 350 nm-360 nm) light-emitting diodes(LEDs) each with specifically designed irregular sawtooth electron blocking layer(EBL) by using the APSYS simulation program.The internal quantum efficiencies(IQEs),light output powers,carrier concentrations in the quantum wells,energy-band diagrams,and electrostatic fields are analyzed carefully.The results indicate that the LEDs with composition-graded pAl_xGa_(1-x)N irregular sawtooth EBLs have better performances than their counterparts with stationary component p-AlGaN EBLs.The improvements can be attributed to the improved polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-AlGaN interface,which results in less electron leakage and better hole injection efficiency,thus reducing efficiency droop and enhancing the radiative recombination rate.     

Spectral and ion emission features of laser-produced Sn and SnO_2 plasmas

We have made a detailed comparison of the atomic and ionic debris, as well as the emission features of Sn and SnO_2 plasmas under identical experimental conditions. Planar slabs of pure metal Sn and ceramic SnO_2 are irradiated with1.06 μm, 8 ns Nd:YAG laser pulses. Fast photography employing an intensified charge coupled device(ICCD), optical emission spectroscopy(OES), and optical time of flight emission spectroscopy are used as diagnostic tools. Our results show that the Sn plasma provides a higher extreme ultraviolet(EUV) conversion efficiency(CE) than the Sn O2 plasma.However, the kinetic energies of Sn ions are relatively low compared with those of SnO_2. OES studies show that the Sn plasma parameters(electron temperature and density) are lower compared to those of the SnO_2 plasma. Furthermore, we also give the effects of the vacuum degree and the laser pulse energy on the plasma parameters.     

Calibration of a compact XUV soft X‐ray monochromator with a digital autocollimator in situ

A digital autocollimator of resolution 0.1 µrad (0.02 arcsec) serves as a handy correction tool for calibrating the angular uncertainty during angular and lateral movements of gratings inside a monochromator chamber under ultra‐high vacuum. The photon energy dispersed from the extreme ultraviolet (XUV) to the soft X‐ray region of the synchrotron beamline at the Taiwan Light Source was monitored using molecular ionization spectra at high resolution as energy references that correlate with the fine angular steps during grating rotation. The angular resolution of the scanning mechanism was <0.3 µrad, which results in an energy shift of 80 meV at 867 eV. The angular uncertainties caused by the lateral movement during a grating exchange were decreased from 2.2 µrad to 0.1 µrad after correction. The proposed method provides a simple solution for on‐site beamline diagnostics of highly precise multi‐axis optical manipulating instruments at synchrotron facilities and in‐house laboratories.     

A confident source of hard X‐rays: radiation from a tokamak applicable for runaway electrons diagnosis

In a tokamak with a toroidal electric field, electrons that exceed the critical velocity are freely accelerated and can reach very high energies. These so‐called `runaway electrons' can cause severe damage to the vacuum vessel and are a dangerous source of hard X‐rays. Here the effect of toroidal electric and magnetic field changes on the characteristics of runaway electrons is reported. A possible technique for runaways diagnosis is the detection of hard X‐ray radiation; for this purpose, a scintillator (NaI) was used. Because of the high loop voltage at the beginning of a plasma, this investigation was carried out on toroidal electric field changes in the first 5 ms interval from the beginning of the plasma. In addition, the toroidal magnetic field was monitored for the whole discharge time. The results indicate that with increasing toroidal electric field the mean energy of runaway electrons rises, and also an increase in the toroidal magnetic field can result in a decrease in intensity of magnetohydrodynamic oscillations which means that for both conditions more of these high‐energy electrons will be generated.