Effects of electron radiation on shielded space and triple-junction GaAs solar cells

The displacement damage dose methodology for analysing and modelling the performance of triple-junction InGaP₂/GaAs/Ge solar cells in an electron radiation environment is presented. Degradations at different electron energies are correlated with displacement damage dose (D_\rm d). One particular electron radiation environment, relative to a geosynchronous earth orbit (GEO), is chosen to calculate the total D_\rm d behind the different thicknesses coverglasses to predict the performance degradation at the end of the 15-year mission.     

用于空间激光通信的InGaAsP激光二极管辐射损伤研究（英文）

对1.55μm波长DFB结构的In Ga As P多量子阱激光二极管开展电子和60Co-γ射线辐照试验。试验结果表明,激光二极管的斜度效率主要受带电粒子沉积的电离总剂量影响,而阈值电流和光功率主要受位移损伤剂量的影响。利用位移损伤剂量方法评价激光二极管的辐射损伤特征,并且预测其在空间辐射环境中的光功率衰退情况。模拟计算结果表明,MEO轨道辐射环境对激光二极管光功率辐射损伤远大于GEO轨道的影响,这主要是由于MEO轨道辐射环境的高能电子通量密度远大于GEO轨道的通量密度。     

Influences of quantum noises on direct-modulated properties of 1.3-μm InGaAsP/InP laser diodes

Due to the zero dispersion point at 1.3μm in optical fibres, 1.3-μm InGaAsP/InP laser diodes have become main light sources in fibre communication systems recently. Influences of quantum noises on direct-modulated properties of single-mode 1.3-μm InGaAsP/InP laser diodes are investigated in this article. Considering the carrier and photon noises and the cross-correlation between the two noises, the power spectrum of the photon density and the signal-to-noise ratio (SNR) of the direct-modulated single-mode laser system are calculated using the linear approximation method. We find that the stochastic resonance (SR) always appears in the dependence of the SNR on the bias current density, and is strongly affected by the cross-correlation coefficient between the carrier and photon noises, the frequency of modulation signal, and the photon lifetime in the laser cavity. Hence, it is promising to use the SR mechanism to enhance the SNR of direct-modulated InGaAsP/InP laser diodes and improve the quality of optical fibre communication systems.     

Degradation mechanisms of current gain in NPN transistors

An investigation of ionization and displacement damage in silicon NPN bipolar junction transistors (BJTs) is presented. The transistors were irradiated separately with 90-keV electrons, 3-MeV protons and 40-MeV Br ions. Key parameters were measured {\em in-situ} and the change in current gain of the NPN BJTS was obtained at a fixed collector current (I_{\rm c}=1~mA). To characterise the radiation damage of NPN BJTs, the ionizing dose D_{\i} and displacement dose D_{\d} as functions of chip depth in the NPN BJTs were calculated using the SRIM and Geant4 code for protons, electrons and Br ions, respectively. Based on the discussion of the radiation damage equation for current gain, it is clear that the current gain degradation of the NPN BJTs is sensitive to both ionization and displacement damage. The degradation mechanism of the current gain is related to the ratio of D_{\rm d}/(D_{\rm d}+D_{\rm i}) in the sensitive region given by charged particles. The irradiation particles leading to lower D_{\rm d}/(D_{\rm d}+D_{\rm i}) within the same chip depth at a given total dose would mainly produce ionization damage to the NPN BJTs. On the other hand, the charged particles causing larger D_{\rm d}/(D_{\rm d}+D_{\rm i}) at a given total dose would tend to generate displacement damage to the NPN BJTs. The Messenger--Spratt equation could be used to describe the experimental data for the latter case.     

Correlation between Displacement Damage Dose and Proton Irradiation Effects on GaInP/GaAs/Ge Space Solar Cells

The irradiation effects of 0.28-2.80 MeV protons on GalnP/GaAs/Ge solar cells have been analysed, and then correlated with the displacement damage dose. The results of I-V and spectral response measurements, combined with the SRIM-derived vacancies produced rates, show that the degradation of the solar cells is largely determined by the displacement damage of the GaAs sub-cell. Thus the SRIM-derived NIEL values for protons in the GaAs sub-cell are used to calculate the displacement damage dose. It is shown that the irradiation effects of the solar cells caused by protons at different energies are correlated well with the aid of displacement damage dose.     

Time delay in InGaN multiple quantum well laser diodes at room temperature

This paper reports that a long delay between the beginning of pumping current pulse and the onset of optical pulse is observed in InGaN laser diodes.The delay time decreases as the pumping current increases,and the speed of the delay time reduction becomes slower as the current amplitude increases further.Such delay phenomena are remarkably less serious in laser diodes grown on GaN substrate than those on sapphire.It attributes the delay to the traps which cause a large optical loss by saturable absorption and retard the laser action.The traps can be bleached by capturing injected carriers.The effect of GaAs laser irradiation on InGaN laser action demonstrates that the traps responsible for the delay are deep centres which can be filled by the photo-assisted processes.     

Radiation effects on MOS and bipolar devices by 8 MeV protons, 60 MeV Br ions and 1 MeV electrons

The radiation effects of the metal-oxide-semiconductor (MOS) and the bipolar devices are characterised using 8~MeV protons, 60~MeV Br ions and 1~MeV electrons. Key parameters are measured {\it in-situ} and compared for the devices. The ionising and nonionising energy losses of incident particles are calculated using the Geant4 and the stopping and range of ions in matter code. The results of the experiment and energy loss calculation for different particles show that different incident particles may give different contribution to MOS and bipolar devices. The irradiation particles, which cause larger displacement dose within the same chip depth of bipolar devices at a given total dose, would generate more severe damage to the voltage parameters of the bipolar devices. On the contrary, the irradiation particles, which cause larger ionising damage in the gate oxide, would generate more severe damage to MOS devices. In this investigation, we attempt to analyse the sensitivity to radiation damage of the different parameter of the MOS and bipolar devices by comparing the irradiation experimental data and the calculated results using Geant4 and SRIM code.     

Femtosecond Laser Induced Optical Waveguides and Micro—mirrors Inside Glasses

Optical Waveguides and micro-mirrors have been successfully induced inside fused silica glass and k9 glass,respectively,by focusing a 800nm femtosecond(fs)pulsed laser with a repetition rate of 1kHz,The change of refractive index was determined to be 0.001-0.008 in the fused silica glass and 0.006 in the k9 glass.The refractive index change is dependent on both the dose of irradiation and the power density of the fs pulsed laser,Photoluminescence was observed in the irradiated region,and was attributed to the defects induced by fs laser irradiation.We discuss the relationship between the optical property and the luminescent propert property of the irradiated region.     

A tunnel regenerated coupled multi-active-region large optical cavity laser with a high quality beam

A novel coupled multi-active-region large optical cavity structure cascaded by a tunnel junction is proposed to solve the problems of facet catastrophic optical damage (COD) and the large vertical divergence caused by the thin emitting area in conventional laser diodes. For a laser with three active regions, a slope efficiency as high as 1.49 W/A, a vertical divergence angle of 17.4 , and a threshold current density of 271 A/cm 2 are achieved. By optimizing the structural parameters, the beam quality is greatly improved, and the level of the COD power increases by more than two times compared with that of the conventional laser.     

初始电子密度对光学薄膜激光损伤机制的影响

光学元件的激光损伤问题是激光器件向高功率密度方向发展中必须认识和克服的问题.基于Forkker-Planck方程,研究了激光与材料相互作用时的雪崩电离机制、多光子电离机制以及联合两种机制的情况.雪崩电离的产生需要一定密度的初始自由电子存在,该自由电子可以是材料中原本就存在的,也可能是光电离产生的.着重分析了材料中的初始自由电子对材料电离机制的影响.结果表明,雪崩过程在激光作用一段时间后会达到一个稳定的电离阶段(以自由电子平均能量不随时间变化为特征,且此时雪崩电离为材料电离的主导机制),该时间与光电离速率、材料中初始自由电子密度有关.材料中的初始自由电子可以在一定程度上掩盖光电离的作用效果.     

初始电子密度对光学薄膜激光损伤机制的影响

光学元件的激光损伤问题是激光器件向高功率密度方向发展中必须认识和克服的问题.基于Forkker-Planck方程,研究了激光与材料相互作用时的雪崩电离机制、多光子电离机制以及联合两种机制的情况.雪崩电离的产生需要一定密度的初始自由电子存在,该自由电子可以是材料中原本就存在的,也可能是光电离产生的.着重分析了材料中的初始自由电子对材料电离机制的影响.结果表明,雪崩过程在激光作用一段时间后会达到一个稳定的电离阶段（以自由电子平均能量不随时间变化为特征,且此时雪崩电离为材料电离的主导机制）,该时间与光电离速率、材料中初始自由电子密度有关.材料中的初始自由电子可以在一定程度上掩盖光电离的作用效果.
关键词:初始电子;激光损伤;光电离;雪崩电离     

Laser diode beam shaping by optical interference

We recently proposed a novel beam shaping technique that employs Lloyd’s mirror interference. In this study, we apply this technique to three commercial laser diodes: laser diodes used for optical pumping of solid-state lasers, for laser beam printers, and for laser displays. The elliptical output beams from these laser diodes could be transformed into nearly circular beams by inserting a mirror-polished GaAs substrate below the active layer of each laser diode and adjusting its height. The experimentally observed far-field patterns were predicted fairly well by numerical calculations based on Huygens’ integral. We confirmed that our beam shaping technique is applicable to laser diodes with various wavelengths and vertical beam divergence angles. We also describe the monolithic configuration of the beam shaping system, which can be fabricated by dry etching.     

Determination of Rubipium Using Laser Diode Excited Atohic Fluorescence

The use of laser diodes to excite atomic fluorescence for chemical analysis is investigated. Operating conditions for the laser diode, optical schematic, results, and calibration curve are provided.     

四光束对高能电子的捕获特性研究

依据非线性强场效应的基本原理,提出了一种四光束捕获电子的方案,旨在通过延长电子和强场相互作用时间来提高非线性过程发生的总概率,实现观测信号的增强。其基本原理是基于电子在强激光光束上的非弹性散射。数值模拟结果表明,捕获后的电子和中心光场的相互作用时间得到延长。     

1 064 nm激光对氧化铟锡薄膜的损伤研究

 液晶光学器件在激光光束精密控制上具有重要应用前景,氧化铟锡（ITO）薄膜作为液晶光学器件的透明导电电极,是液晶器件激光损伤的薄弱环节。为此,建立了ITO薄膜激光热损伤物理模型。理论计算结果表明：1 064 nm激光对ITO薄膜的损伤主要为热应力损伤;连续激光辐照下,薄膜损伤始于靠近界面的玻璃基底内;脉冲激光辐照下,温升主要发生在光斑范围内的膜层,薄膜损伤从表面开始。利用泵浦探测技术,研究了ITO薄膜的损伤情况,测量了不同功率密度激光辐照后薄膜的方块电阻,结合1-on-1法测定了ITO薄膜的50%损伤几率阈值。实验结果表明：薄膜越厚,方块电阻越小,激光损伤阈值越低;薄膜未完全损伤前,方块电阻随激光功率密度的增加而增大。理论计算与实验结果吻合较好。设计液晶光学器件中的ITO薄膜电极厚度时,应综合考虑激光损伤、透光率及薄膜电阻的影响。     

紫外准分子激光损伤典型光学材料的特性分析

根据已经建立的紫外准分子激光损伤典型光学材料的理论模型,研究了准分子激光对透明光学材料（石英玻璃）和非透明光学材料（K9玻璃）的损伤特性,并结合实验结果证实了理论模型的有效性。研究表明：在准分子激光对非透明光学材料辐照下,激光光斑半径越大,产生的热应力和温度越小;脉宽越小,产生的热应力越大;随着脉冲数的增加,温度和热应力都逐渐增大。值得注意的是,当重频增加至45 Hz以上时,熔融损伤阈值开始低于应力损伤阈值,这说明当重频增加到一定程度时,非透明光学材料将首先产生熔融损伤,而不再是应力损伤。在准分子激光对透明光学材料辐照下,杂质微粒的半径和掩埋深度对光学材料温度场分布有着重要影响。但当杂质半径和掩埋深度超过一定的数值时,杂质粒子的存在与表面温度并无联系。理论模型能够较好地解释石英玻璃前/后表面相同的初始损伤形貌特征。     

Period Doubling in a Fabry-Perot Laser Diode Subject to Optical Pulse Injection

Experimental study and numerical simulations of the period doubling of injected optical pulses in Fabry-Perot laser diodes are presented. In our experiments, the period doubling is achieved within a wide input frequency range and the period doubling of the injected optical pulses with 6.32 GHz repetition rate is investigated in detail. The obtained experimental results indicate that period doubling occurs at an appropriate injected optical power level when the bias current of the Fabry-Perot laser diode is located in lower ranges. Moreover, the experimental observed features have been numerically demonstrated by using a coupled rate-equation model. Numerical simulations are consistent with the experimental results.     

Characteristics of Multi-Beam Module Using Waveguides for Laser Scanning Optical Systems

A multi-beam module using optical waveguides has been studied for a laser scanning optical system. Laser diodes with a wavelength of 780 nm are assembled on a silicon substrate. The beams emitted from the laser diodes are directly coupled into waveguides. This multi-beam module is assembled on a metal substrate with a photodiode. The photodiode controls the power of each laser diode on the silicon substrate. The multi-beam module is able to increase the output speed of high-density image printings, and the speed for high-speed color printings. We have developed the four-beam module with beam divergence angles of 11 degrees and spatial beam interval of 24 μm. Additional heat sink and optimizing tip-bonding between the laser diode and solder pad on the silicon substrate is useful to stabilize laser power against rising temperature.     

Optical Defect in GaN-Based Laser Diodes Detected by Cathodoluminescence

GaN-based laser diodes （LDs） with 399 nm wavelength are grown on sapphire substrates by metal organic chemical vapour deposition （MOCVD）. Electroluminescence spectra of the fabricated LDs show that the LDs from some grown wafers failed to emit laser. The SEM and XRD results show the similar surface morphology and interface qualities of multi quantum wells （MQWs） and super-lattices between LDs that succeed and fail to emit laser. However, the cathodoluminescence （CL） measurements reveal a kind of optical defect rather than structural defect in un-emitted LDs. Further depth-dependent CL imaging observation indicates that such optical defects originate from the MQWs to the surface of LDs as a non-irradiative recombination centre that should cause the failure of laser emitting of LDs.