脉冲电流冲击力对电极间距的影响

利用时变场理论和瞬态动力学方程建立了电极及其支撑结构的瞬态耦合模型,分析了瞬态电磁场各参数的分布特点,并求解了电极及其支撑结构的动态响应状态参数。计算结果表明:玻璃钢支撑结构对于脉冲电流形成的冲击力载荷具有很好的缓冲作用;低弹性模量支撑材料在脉冲上升沿和峰值阶段均会产生波动性形变,但该波动性形变对电极间距不会造成太大的影响。     

单壁碳纳米管薄膜光电器件研究

制备了单壁碳纳米管薄膜光电器件,在偏压和激光器照射条件下可产生净光电流。分别研究了偏置电压、激光功率、照射位置对净光电流的影响。实验表明,激光照射薄膜中点,净光电流随着偏压的增大而增大,随激光功率的增大而趋于饱和,偏压为0.2 V,激光功率为22.7 mW时,净光电流达到0.24 μA;无偏压,激光照射薄膜不同位置时,净光电流值关于器件中心对称分布,照射两端点输出最大光电流,照射中点输出趋于“0”。经分析,在偏压和激光照射薄膜中心位置的条件下,器件因内光电效应可产生净光电流;在无偏压和激光照射的条件下,因光热电效应可产生净光电流,并建立了温度模型,根据单壁碳纳米管的热电势特性推导出了净光电流与光照位置的关系,其符合实验结果;内光电和光热电效应是光电流产生、变化的原因,在偏压和激光照射的一般条件下,净光电流应是两种效应的叠加结果。器件所具有的光电特性使其在光伏器件、光传感器有应用的潜力。     

Optoelectronic conversion of short pulses in sub-micrometer GaAs active devices

The accelerating integration of microwave and optical components in modern optoelectronic systems stimulates comprehensive investigations of device operation and efficiency. This paper studies the optoelectronic conversion capabilities of sub-micron GaAs active devices in response to ultra-short illumination pulses. The physical phenomena involved in the photo-electronic effects are appropriately accounted for using a physical device model based on the solution of the Boltzmann’s transport equations. The study targets important optical performance indicators including terminal photocurrent peak value and switching time. A figure-of-merit is defined to quantify the overall response. Results show that operating and geometrical conditions can play important roles in the device design, operation and optimization process.     

激光主动干涉条纹间距识别光学目标口径

利用物理光学相关知识及Collins衍射积分公式和硬边光阑的复高斯函数分解法,推导得到目标处干涉图样条纹间距与光学目标反射光时间分布关系的解析表达式.从原理分析、仿真计算和实验研究等方面研究了干涉场的条纹间距、光学目标口径参数和反射光时间分布包络的峰峰数、峰峰间距和峰峰比之间定量关系.结果表明,当条纹间距的大小约为目标的口径尺寸时,反射光时间分布包络的峰峰数由单峰向多峰过渡,峰峰间距和峰峰比曲线会出现极大值,根据这一变化规律可以估测出光学目标的口径参数,其估测精度受条纹间距可调节范围的影响.     

Characterisation of the influence of multi-quantum barrier reflectors within GaInP/AlGaInP quantum well lasers using near-field imaging techniques

Using a near-field scanning optical microscope, near-field photocurrent and topographic imaging has measured the effect on intrinsic electric fields and photocurrent propagation resulting from inserting multi-quantum barrier (MQB) super-lattices into quantum well lasers. Measurements on devices at two different excitation wavelengths have highlighted the sensitivity of the near-field optical technique. Strong correlations were seen in the photocurrent response of the multi-quantum barrier regions when compared with simulations made on the electric field generated within the structure. As a result, photocurrent attenuation was attributed to carrier confinement in these barrier regions when compared to a control sample. The measurements illustrate the effectiveness of the MQB, in addition to the sensitivity and power of the near-field photocurrent technique.     

Effects of annealing temperature on GO–Cu2O composite films grown by electrochemical deposition for PEC photoelectrode

In this work, graphene oxide–cuprous oxide (GO–Cu₂O) composite films were grown on fluorine-doped tin oxide substrates by electrochemical deposition. We investigated the effects of the annealing temperature on the morphological, structural, optical and photoelectrochemical (PEC) properties of GO–Cu₂O composite films. As a result, our work shows that while GO–Cu₂O composite films exhibit the highest XRD (111) peak intensity at 300 °C sample, the highest photocurrent density value obtained was −4.75 mA/cm² at 200 °C sample (using 0.17 V versus a reversible hydrogen electrode (RHE)). In addition, a reduction reaction at 300 °C sample was observed using XPS analysis from the shift in the O1s peak in addition to a weaker O1s peak intensity.     

Visible photocurrent response of TiO2 anode

The photoelectrochemical response to the electromagnetic radiation over the visible range is particularly sought for from the point of view of the efficiency of hydrogen generation by water photolysis in a photoelectrochemical solar cell, PEC. The PEC used in this work comprises thin film TiO₂ - based photoanode, Pt foil covered with Pt black as a cathode and SCE as a reference electrode, immersed in an electrolyte solution. Titanium dioxide thin films are deposited by means of rf reactive sputtering and modified, when necessary, by Au or Ag ultra-thin overcoatings. Here we show that even unmodified TiO₂ photoanode, shows a photocurrent peak over the visible range of the light spectrum (λ = 500-650 nm). The effect of the surface modification by noble metals and properties of the aqueous electrolyte on the visible photocurrent are studied. The optical spectra indicate an increased absorption due to noble metal deposits at 410 nm for Ag and at 600 nm for Au. In contrast, the photocurrent peak over the visible range (500 nm < λ < 650 nm) changes its symmetry and decreases in intensity with the increasing thickness of noble metals layers. The visible photoresponse is explained in terms of OH formation at the interface between TiO₂ electrode and aqueous electrolyte.     

Multi-wavelength Brillouin-Raman ring-cavity fiber laser with 22-GHz spacing

We experimentally demonstrate a multi-wave length Brillouin-Raman fiber laser configured in a ring-cavity resonator. Interactions between stimulated Brillouin scattering and Raman amplification in a dispersion compensating fiber, attributed to the generation of 16 output channels at injected Raman pump unit power of 650 mW and Brillouin pump power of 2.0 mW. The first output channel has a peak power of 14.8 mW. By discriminating the even-order Brillouin Stokes signals from circulating in the resonator, the generated output channels were found to have wavelength spacing of ∼22 GHz. The output channels were also found to have average optical signal-to-noise ratio value of 11.7 dB.     

Correlated ejection of electron-hole drops from a continuously generated electron-hole liquid in Ge

The photocurrent power spectra were measured in a Ge photodiode as a function of the incident optical intensity at 1.8 K and 4.3 K. The observed spectra showed a peak at low frequencies superimposed on a continuum which has a cut-off at high frequency. The interpretation of the results implies that the electron-hole drops coming from a same region of the photoexcited liquid are ejected periodically.     

Generation and transmission of the double-sideband optical millimeter-wave with signal carried only by optical carrier

In this paper, we have proposed a new scheme to generate double-sideband (DSB) optical millimeter-wave (mm-wave) with signal carried only by optical carrier, and its transmission performance is investigated. The theoretical and numerical results show that the DSB optical mm-wave signal generated by our scheme suffers only from the fading effect, the time shift of the sidebands has little influence on its transmission performance. The signal demodulated from the harmonic photocurrent shows a clear and open eye diagram and has good performance even if the transmission distance is very close to but not just at the fading nodes. The theoretical results are in good agreement with our numerical simulation.     

Entwicklung leistungsfähiger Stickstofflaser mit abgeschmolzenem Laserrohr

For an increase of the laser pulse energy from longitudinally excited multiple electrodes tubes, experiments and model calculations have been accomplished. A variation of the electrode spacing in the laser tube has shown, that a maximum pulse energy could be achieved with about 40 mm electrode spacing. If barium titanat capacitors with a dielectric constant of 10000 in the pulse forming unit were applied, a voltage pulse transform occured enabling an increase of the laser power up to 50%. With a sealed off operated laser tube of 100 cm active length, a laser peak power of 600 kW and a pulse duration of 10 ns could be achieved. A tube with 200 cm active length generated a pulse power of 1.2 MW. The decrease of laser pulse energy with increasing pulse repetition rate can be explained by the decrease of impulse breakdown voltage. For an increase of the lifetime of laser tubes, appropriate technologies for the production of the tube have been developed.     

Multi-wavelength fiber source with equal frequency spacing

A optical filter based on Sagnac interferometer was proposed to be acted as a comb filter with equal frequency spacing and good signal to noise ratio (SNR), which was composed of an 8.14 m stress-induced Hi-Bi (high-birefringence) PM (polarization-maintaining) fiber. Using this multi-wavelength Sagnac comb filter and a gain flattening Sagnac filter that made the output spectra flattening at different pump powers, a 25-channel multi-wavelength all-fiber source were successfully generated with channel spacing of 0.8 nm with respect to the center wavelength at 1550 nm and flattened gain about ±1 dB peak deviation. The channel spacing can be further reduced to 0.4 nm to produce a DWDM (dense wavelength division multiplexing) source, simply by increasing the Hi-Bi fiber to be 16.28 m. It can be used in many applications such as WDM (wavelength division multiplexing), optical amplifiers with a high SNR, narrow band filters and optical sensors.     

不对称菁染料敏化纳米TiO2的光生电流过程

用光电化学方法研究了不对称菁类染料敏化TiO2 纳米结构电极的光电转换过程 .结果表明 ,该染料的电子激发态能级位置与TiO2 纳米粒子导带边位置匹配较好 ,光激发染料后 ,其激发态电子可以注入到TiO2 纳米多孔膜的导带 ,从而使TiO2 纳米结构电极的吸收光谱和光电流谱红移至可见光区 ,其IPCE(Incidentphoton to electronconversionefficiency)值最高可达 84.3 % .并进一步结合现场紫外 可见吸收光谱研究了外加电势对激发态染料往TiO2 纳米多孔膜注入电子过程的影响     

Analysis and interpretation of photo-stimulated discharge spectrum for polypropylene films under different electric and geometrical conditions

Experiments on polypropylene films under different electric and geometrical conditions are carried out to investigate various causes that would affect the interpretation of photo-stimulated discharge spectrum. The samples used in the experiment are metalized with finger-like shape or circular shape electrodes. The results show that the occurrence of photoemissions from electrode or polymer at wavelengths less than about 260 nm is possible, depending on the polarity and amplitude of applied voltage. The photocurrent spectra for samples with circular electrodes characterize two charge de-trapping peaks and the peak at 273 nm is also partially contributed by the photoelectrons from electrode.     

Terahertz generation from Si3N4 covered photoconductive dipole antenna

We observe enhanced terahertz (THz) radiation generated from a Si3N4 film-coated GaAs photoconductive dipole antenna. Compared to an uncoated antenna with identical electrode geometry and optical excitation power, the Si3N4 film-coated antenna has a higher effective DC resistance and larger breakdown voltage. As a result, the peak amplitude of generated THz radiation is significantly enhanced due to the Si3N4 film-coated layer.     

Anisotropy of photocurrent for two-photon absorption photodetector made of hemispherical silicon with $(\overline{1}10)$ plane

We fabricated a hemispherical nearly-intrinsic Si-based photodetector with ( plane. The photocurrent generated from the detector under a continuous wave laser at the wavelength of 1.3 μm was observed. The photocurrent shows a quadratic dependence on the incident optical power. The dependence of the photocurrent on the azimuth of the incident optical field is consistent with the anisotropy of the two-photon absorption in Si crystals. The ratio of the two nonzero independent components of the third-order susceptibility of silicon is obtained to be 0.42 from the observed result of the anisotropy of the photocurrent.     

Photocurrent in single walled carbon nanotubes

Carbon based nanomaterials have received a lot of attention due to their unique structural and physical properties. In this study, photoresponse in semiconducting single-walled carbon nanotubes is investigated using density functional theory. The photocurrent generated is found to increase with the increasing electrode voltage at a constant flux. In all models the current increases uniformly with applied voltage and maximum value of current is found in the pristine CNT model, however the magnitude of photocurrent decreases in the homogenously nitrogen and boron doped models. Moreover, the photocurrent increases with increase in flux showing photoresistive property in CNTs. The spectral peaks appear at different wavelengths in the three models paving way for wide range of applications in the futuristic optoelectronic devices.     

Experimental research of diffuse bi-directional pulsed dielectric barrier discharge plasma

A bi-directional nanosecond pulsed power supply is employed to generate diffuse dielectric barrier discharge in N₂ using needle-plate electrode configuration at atmospheric pressure. Both discharge images and optical emission spectra of diffuse bi-directional nanosecond high-voltage pulsed dielectric barrier discharge are successfully recorded under severe electromagnetic interference. The diffuse performance of the discharge at different electrode gap distances is observed. The effects of pulse peak voltage, pulse repetition rate, electrode gap distance, He addition, and O₂ addition on the optical emission spectra are investigated. The main physicochemical processes involved are discussed.     

Current-voltage characteristics simulation and analysis of 4H-SiC metal-semiconductor-metal ultraviolet photodetectors

The current-voltage (I-V) characteristics of 4H-SiC metal-semiconductor-metal (MSM) ultraviolet pho-todetector with different finger widths and spacings, different carrier concentrations and thicknesses of n-type epitaxial layer are simulated. The simulation results indicate that the dark current and the pho-tocurrent both increase when the finger width increases. But the effect of finger width on the dark current is more significant. On the other hand, the effect of finger spacing on the photocurrent is more significant. When the finger spacing increases, the photocurrent decreases and the dark current is almost changeless. In addition, it is found that the smaller the carrier concentration of n-type epitaxial layer is, the smaller the dark current and the larger the photocurrent wiU be. It is also found that I-V characteristics of MSM detector also depend on the epitaxial layer thickness. The dark current of detector is smaller and the photocurrent is larger when the epitaxial layer thickness is about 3 μm.     

The transmission performance of the single sideband optical millimeter-wave with BPSK signal in the duplex radio-over-fiber link

This paper has investigated the transmission performance of the single sideband (SSB) optical millimeter (mm)-wave with signal carried by the sideband in BPSK format in duplex radio-over-fiber (RoF) system theoretically and numerically. The SSB optical mm-wave signal is generated by a LiNbO₃ Mach–Zehnder modulator and there exists an optimal modulation index to generate the SSB optical mm-wave with a maximal RF photocurrent. The SSB optical mm-wave is much suitable for the duplex ROF link with the uplink lightwave recovered from the downlink because the optical carrier carries no signal. In such a duplex RoF link, although there are the spurs on the optical carrier, they have little influence on the downlink and the uplink signal even if the modulation index is large.