Lasing of CdSexS1-x quantum dots in a glass spherical microcavity

A glass spherical microcavity only a few microns in diameter embedded with CdSexS1-x quantum dots (QDs) was fabricated using a physical method; it exhibited good optical stability under continuous-wave laser excitation with high power. We investigated the excitation power dependences of the emission intensity and the linewidth of both transverse electric and transverse magnetic resonance peaks of whispering gallery modes. Stimulated emission behaviour of multi-frequency modes is observed at room temperature. The low threshold value and large mode separation makes QD-containing microspheres promising for visible microlaser applications.

Room-temperature, ground-state lasing for red-emitting vertically aligned InAlAs/AlGaAs quantum dots grown on a GaAs(100) substrate

The effect of the growth temperature on the properties of InAlAs/AlGaAs quantum dots grown on GaAs(100) substrates is investigated. The optical efficiency and structural uniformity are improved by increasing the growth temperature from 530 to 560 degreesC. The improvements of InAlAs/AlGaAs quantum-dot characteristics could be explained by suppressing the incorporation of oxygen and the formation of group-III vacancies. Furthermore, edge-emitting laser diodes with six quantum-dot layers grown at 560 degreesC have been fabricated. Lasing occurs via the ground state at 725 nm, with a room-temperature threshold current density of 3.9 kA/cm(2), significantly better than previously reported values for this quantum-dot systems. (C) 2002 American Institute of Physics.

AlGaInP visible quantum well lasers for information technology

650 nm-range AlGaInP multi-quantum well (MQW) laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) have been studied and the results are presented in this paper. Threshold current density of broad area contact laser diodes can be as low as 350 A/cm(2). Laser diodes with buried-ridge strip waveguide structures were made, threshold currents and differential efficiencies are (22-40) mA and (0.2-0.7) mW/mA, respectively. Typical output power for the laser diodes is 5 mW, maximum output power of 15 mW has been obtained. Their operation temperature can be up to 90 degrees C under power of 5 mW. After operating under 90 degrees C and 5 mW for 72 hrs, the average increments for the threshold currents of the lasers at 25 degrees C and the operation currents at 5 mW (at 25 degrees C) are (2-3) mA and (3-5) mA, respectively. Reliability tests showed that no obvious degradation was observed after 1400 hours of CW operation under 50 degrees C and 2.5 mW.

A New Technique for Side Pumping of Double-Clad Fiber Lasers

We report a new technique, called SAP, for side pumping of double-clad, rare-earth-doped fiber lasers using fiber-coupled pump sources. The highest coupling efficiency can even exceed 92% in theory with this structure.

Controlled growth of III-V compound semiconductor nano-structures and their application in quantum-devices

Various techniques on the growth of self-assembled compound semiconductor nano-structures (quantum dots, QDs) have been tried to enhance the controlling on size, density, emitting wavelength, uniformity in size and ordering in location of the QDs. Optimized growth conditions have been used in the application of the QD materials in opto-electronic devices. High-power long-lifetime quantum-dot laser-diodes (QD-LDs) emitting near 1 mu m, QD-LDs emitting in red-light range, 1.3 mu m QD-LDs on GaAs substrate and quantum-dot super-luminescent diodes (QD-SLDs) have successfully been achieved.

A novel photonic crystal vertical cavity surface emitting laser based on coherent coupling

We demonstrate a novel oxide confined GaAs-based photonic crystal vertical cavity surface emitting laser (PC-VCSEL) operating at a wavelength of 850 nm based on coherent coupling. A ring-shaped light-emitting aperture is added to the conventional PC-VCSEL, and coherent coupling is achieved between the central defect aperture and the ring-shaped light-emitting aperture. Measurements show that under the continuous-wave (CW) injected current of 20 mA, a high power of 2 mW is obtained, and the side mode suppression ratio (SMSR) is larger than 20 dB. The average divergence angle is 4.2 degrees at the current level of 20 mA. Compared with the results ever reported, the divergence angle is reduced.

Tunable parametric fluorescence using a single crystal

In this paper, we investigate the mechanism of tunable parametric superfluorescence (PS) based on the second harmonic generation and parametric processes taking place in the same nonlinear crystal (BBO). The tunable spectra of PS has been generated between 480 nm and 530 nm, which is pumped by the second-harmonic from the high-power Ti: sapphire laser system at 1 kHz repetition rate. We present the generation mechanism of PS theoretically and simulate the process of PS ring using the amplification transfer function. The experiment and the theory show that PS will appear when the phase matching angle for second-harmonic generation is close to the optimal pump angle for optical parametric generation, and then the tunable spectra of PS are generated by slightly adjusting the crystal angle. The result provides a theoretical basis for controlling the generation of PS and quantum entanglement states, which is of great significance for the development of quantum imaging, quantum communications and other applieations.

THE DEPENDENCE OF THE INVERSION LAYER THICKNESS ON THE FILM THICKNESS IN THIN-FILM SOI STRUCTURES

The dependence of the inversion-layer thickness on the film thickness in thin-film SOI structure is analyzed theoretically by using computer simulation. A new concept and parameter, the critical thickness of thin film all-bulk inversion, is introduced for the design of thin-film MOS/SOI devices. It is necessary to select the film thickness T(s1) close to the all-bulk strong inversion critical thickness in order to get high-speed and high-power operation of ultra-thin film MOS/SOI devices.

Fiber Optic Coupling of CW Linear Laser Diode Array

Based on a set of microoptics the output radiation from a continuous wave (CW) linear laser diode array is coupled into a multi-mode optical fiber of 400 ptm diameter. The CW linear laser diode array is a 1 cm laser diode bar with 19 stripes with 100 fxm aperture spaced on 500 (xm centers. The coupling system contains packaged laser diode bar, fast axis collimator, slow axis collimation array, beam transformation system and focusing system. The high brightness, high power density and single fiber output of a laser diode bar is achieved. The coupling efficiency is 65% and the power density is up to 1.03 * 10~4 W/cm~2.

Design of side-pumped Nd : YAG lasers

Design of the typical laser diode side-pumped Nd:YAG rod system has been discussed using the conventional ray tracing method in this paper. Firstly introduce two basic matrices, refractional and translational matrix, described the transmission of nonparaxial light ray in the medium without concerning the absorption of light. And then, using those matrices, analyze the distribution of pump light in the crystal respectively under the condition of directly pumped system and indirectly pumped system with a cylindrical quartz rod as focusing lens. From the result of simulation, we compare the advantage and disadvantage of the two pumped method, and mainly consider how to select the diameter of the focus lens and cooling tube, indicate the effect of deionized water and cooling tube have on the pump light distribution in the active material. At last, make some conclusions about the side-pumped Nd:YAG laser system.

Studies of 6H-SiC devices

Silicon carbide (SiC) is recently receiving increased attention due to its unique electrical and thermal properties. It has been regarded as the most appropriate semiconductor material for high power, high frequency, high temperature, and radiation hard microelectronic devices. The fabrication processes and characterization of basic device on 6H-SiC were systematically studied. The main works are summarized as follows:The homoepitaxial growth on the commercially available single-crystal 6H-SiC wafers was performed in a modified gas source molecular beam epitaxy system. The mesa structured p(+)n junction diodes on the material were fabricated and characterized. The diodes showed a high breakdown voltage of 800 V at room temperature. They operated with good rectification characteristics from room temperature to 673 K.Using thermal evaporation, Ti/6H-SiC Schottky barrier diodes were fabricated. They showed good rectification characteristics from room temperature to 473 K. Using neon implantation to form the edge termination, the breakdown voltage was improved to be 800 V.n-Type 6H-SiC MOS capacitors were fabricated and characterized. Under the same growing conditions, the quality of polysilicon gate capacitors was better than Al. In addition, SiC MOS capacitors had good tolerance to gamma rays. (C) 2002 Published by Elsevier Science B.V.

AlGaInP visible quantum well lasers for information technology

650 nm-range AlGaInP multi-quantum well (MQW) laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) have been studied and the results are presented in this paper. Threshold current density of broad area contact laser diodes can be as low as 350 A/cm(2). Laser diodes with buried-ridge strip waveguide structures were made, threshold currents and differential efficiencies are (22-40) mA and (0.2-0.7) mW/mA, respectively. Typical output power for the laser diodes is 5 mW, maximum output power of 15 mW has been obtained. Their operation temperature can be up to 90 degrees C under power of 5 mW. After operating under 90 degrees C and 5 mW for 72 hrs, the average increments for the threshold currents of the lasers at 25 degrees C and the operation currents at 5 mW (at 25 degrees C) are (2-3) mA and (3-5) mA, respectively. Reliability tests showed that no obvious degradation was observed after 1400 hours of CW operation under 50 degrees C and 2.5 mW.

Broadly Tunable Grating-Coupled External Cavity Laser With Quantum-Dot Active Region

A broadly tunable and high-power grating-coupled external cavity laser with a tuning range of more than 200 nm and a similar to 200-mW maximum output power was realized, by utilizing a gain device with the chirped multiple quantum-dot (QD) active layers and bent waveguide structure. The chirped QD active medium, which consists of QD layers with InGaAs strain-reducing layers different in thickness, is beneficial to the broadening of the material gain spectrum. The bent waveguide structure and facet antireflection coating are both effective for the suppression of inner-cavity lasing under large injection current.

Study of the LED based light calibration system for neutron wall detector

The light calibration system is one of the key components of Neutron Wall detector. It is used to calibrate the electronics and to monitor the long-term stability of the detector modules. With the detaile investigations, a calibration system with high-power LED (3W) driven by the fast pulses has been carried out. It is also tested together with the detector module of the Neutron Wall and the result of the preliminary calibration demonstrates that it fulfills the needs. It's a new design proposal to the light calibration system of the fast scintillator detector.

大功率电子加速器的预研与束流传输的研究

电子束辐照烟道气脱除502和NOx技术是一项将辐射物理和辐射化学紧密结合的高新技术。该项技术自1970年被提出后，经历了20多年的逐步发展，已进入了工业装置阶段。目前，在美国、德国、日本、波兰和我国的成都热电厂等处建立了中试厂和工业示范厂。当前在国际上，对一该项目的关键部件电子加速器有两种方案：即日新公司的高压变压器方案和以俄罗斯新西伯利亚核物理研究所的ElV型加速器为代表的谐振变压器型。根据目前国内的实际状况和满足我所及在兰州各研究所的物理实验的需要，中利4院近代物理所在已有技术力量的基础上，并在国家计委的大力支持下，立项研制大功率谐振变压器型电子加速器。这篇论文首先对1.5Mev/300mA三相谐振变压器型电子加速器的高压电极表面电场强度、分布电容、电感、三相谐振频率等作了预研。在此基础上，着重对强流静电加速管轴上电位和电场分布、平面电子枪的实际电流密度、电极膜孔透镜对束流的聚焦性能、加速管中电子轨迹和出射斜率、球面阴极的电子光学特性等作了详细的计算和分析，从计算得到的结果来看，所设计的电场能够满足束流传输的要求。另外，还对加速管非均匀场对电子负载的抑制作用，离子反轰阴极作了初步研究。论文的另一个重点是研究了静电加速管中强流电子束的空间电荷效应。根据实际情况，合理地建立了物理模型。并对模型上的4个不同位置的束内外径向电位分布、空间电荷对轴＿L电位的影响，以及空间电荷力对束流传输的影响等进行了详尽的理论计算和分析。在对轴上电场分布进行分析时，发现可以将电场沿轴向分为3个区域，并认真对每个区域的作用作了详细的分析说明。特别指出了，强流静电加速管的设计关键在加速管的前端，与弱流加速管相比，前者的变化幅度要大得多。论文最后对大功率电子加速器部件的加工和三相谐振变压器高压发生器模拟实验结果给予了介绍和分析。