熔石英亚表面横向划痕调制作用的3维模拟

建立了熔石英后表面3维横向划痕模型,并采用3维时域有限差分方法对熔石英亚表面划痕周围的电场强度进行了数值模拟,分析了划痕宽度、深度、长度以及划痕倾斜角度对入射光场的调制作用,结果表明:随划痕深度和划痕长度的增加,熔石英内的最大电场强度增大,且当划痕长度达到1μm以上时,最大电场强度趋于稳定;划痕结构因子在1~2之间的划痕较容易引起熔石英损伤;而入射激光在划痕界面和后表面之间发生内全反射时,后表面上的光强增强效果更加明显,因此减少角度范围在20.9°~45°之内的划痕能大幅提高熔石英的损伤阈值。     

The electric field modulation by three-dimensional crack on fused silica subsurface

The main factor of laser-induced damage is the modulation to electromagnetic field of laser by the crack on the subsurface. In this paper, a three-dimensional crack model on the exit surface is presented. Three-dimensional finite-difference time-domain (FDTD) method is employed to simulate the electric field intensity distribution in the vicinity of crack on fused silica subsurface. The roles of the crack width, depth, length and the gradient angle in the modulation to the incident light field are analyzed in detail. Results show that the crack size plays an important role in the electric modulation. With the increasing depth and width, the peak value of maximal electric field intensity appears in fused silica. However, the maximal electric field intensity tends to be a constant when the crack length reaches 1 μm. Besides, the enhancement of light intensity becomes obvious when total internal reflection occurs in fused silica. Our calculated results provide an advisable theoretical criterion to the corresponding experiment.     

Über die Verstärkung der Röntgenlumineszenz durch elektrische Felder und infrarote Strahlung

The x-ray excited luminescence of a zinc-cadmium sulfide phosphor activated by manganese and cobalt can be enhanced by infrared or red light, by alternating electric fields, and by both together. The infrared light as well as the electric field enhance the same emission band caused by manganese. The dependence of the enhancement on the strength and on the frequency of the electric field, and on the intensity and on the wavelength of the stimulating radiation has been investigated. Maximum enhancements are observed at frequencies of about 20 cps and at wavelengths of 0.77 and 1.35 μ of the stimulating light. When both the electric field and the stimulating light are applied together, the enhancement is lower than the sum of both effects. While at small intensities of the infrared the emission is increased by an additional electric field, it is diminished at high intensities. If the non-excited phosphor is exposed to the infrared a memory effect is found quite similar to that produced by electric fields reported byDestriau. The results are discussed using a model published earlier.     

All-Optical Photorefractive Effect in Carbazole-Based Azo-Side Group Polymer

We observe the photorefractivity without bias voltage or prepoling in a bifunctional photorefractive polymer. The maximum two-beam coupling gain is measured to be 126cm^-1 at zero bias voltage. The sample is considered to be poled by the photoinduced longitudinal electric field, which is formed due to the light intensity gradient along the light path. The expression of the electric field was deduced. The energy transfer direction between two writing beams and light intensity dependence of the two-beam coupling gain coefficient is predicted to be consistent with the experimental results. Furthermore, the dependence of the two-beam coupling gain coefficient on external applied electrical field is measured and this experiment verifies the existence of the photoinduced longitudinal electric field.     

基于人工表面等离激元探针实现太赫兹波的紧聚焦和场增强

为提高太赫兹近场显微成像技术的分辨率,设计了一款在Teflon探针的尖锥形表面镀上厚度渐变、具有相同占空比的超薄金属银制条带的探针,用于实现探针尖端处人工表面等离激元的激发和太赫兹波的亚波长聚焦.研究表明,对于频率为0.1 THz的入射波,厚度渐变镀银条带探针产生的紧聚焦光场的尺寸可稳定在20μm左右(λ/150),探针尖端处最大电场强度为入射电场强度的849倍.研究还发现,周期性金属条带的数目和入射电场的偏振方向可对探针尖端处产生的紧聚焦光斑的尺寸和电场强度等进行灵活有效的调控.     

Electric field effect on refraction of light in a layer of chiral liquid crystal with large pitch

The effect of an alternating electric field on the trajectory of an extraordinary light wave in a layer of a chiral liquid crystal with a 180° turn of the director is studied. In this structure, in the absence of the field and at a large angle of incidence of the light wave on the liquid crystal layer, the light undergoes refraction inside the layer. It is shown that the deformation of the director that arises under the action of the electric field changes the character of refraction of the extraordinary wave and the layer begins to transmit the light. The threshold voltage of this effect is determined. The dynamics of the effect is studied. At large voltages, in addition to the extraordinary wave, an ordinary light wave is observed in the light passed through the cell. The ordinary wave intensity is modulated by the initial frequency of the control signal, whereas the extraordinary wave intensity is modulated by the double initial frequency.     

泵浦光激发下金刚石纳米柱内部光场的研究

金刚石纳米柱是实现色心单光子源增强的有效结构,而纳米柱结构尺寸决定泵浦光对色心的激发强度.本文为提高其激发效率,采用时域有限差分法(Finite Difference Time Domain,FDTD)研究金刚石纳米柱的光学性质.通过仿真分析了纳米柱直径和高度对内部电场强度的影响.结果表明,在泵浦光波长为532 nm时...     

静电场中电场强度的数值意义

“近场强远场弱”是静电场的普遍特点,宏观带电体的静电场是点电荷电场叠加的结果.本文以静电场中两个实际的电场强度问题为例,用相对数值比较了电荷分布对电场强度的贡献,阐述电场强度“近场强远场弱”的数值意义.     

Generation and detection of electromagnetic field with charged material oscillation

We generated an electromagnetic field using the spatial oscillation of a charged material such as a polyimide film. The film was vibrated with acoustic waves at 1 Hz–1 kHz. For charged films, changes in electric field intensity with acoustic wave irradiation were detected using an antenna. The electric field intensity and phase were found to be related to the surface voltage and electrical polarity. The surface potential distribution matches the electric field distribution that was measured by scanning the local excitation. These results indicate that this phenomenon can be used to measure the electrical properties of charged materials.     

基于准周期光学超晶格的高效电光调制差频转换

为获得尽可能大的差频转换效率,基于准周期极化铌酸锂(QPPLN)光学超晶格,提出了级联电光和差频理论,用于高效的差频转换。其方法是沿QPPLN光学超晶格的y方向施加一个外加电场,用来控制能量在抽运光、信号光、o偏振的差频光和e偏振的差频光四个光波之间的转移。计算结果表明,在一个100℃,40mm长的QPPLN光学超晶格中,当1550nm信号光与1064nm抽运光光强比值r<0.324时,对光强超过特定值的任意抽运光都可以通过施加一个适当的外加电场将抽运光完全转化为1550nm信号光和3393.4nm差频光;当r≥0.324,只当抽运光光强落在一定范围内时,才可以通过施加外加电场使抽运光完全转化为信号光和差频光;超过该范围,外加电场不能增加差频光转换效率。计算结果还表明,电光调制差频转换效率对温度和畴构造误差都不敏感。     

基于Talbot效应的可调位相差二维六角位相阵列器的理论研究和数值模拟

系统研究了基于Talbot效应的光栅阵列器,利用数值模拟方法开展了阵列器的理论研究,对二维振幅型与固定位相差型阵列器进行了分析,通过外加电场调制位相差可以很好的解决二维振幅型与固定位相差型阵列器后z处光强分布不可调节和工作易受温度影响的问题.推导了外加电场调制位相差位相型阵列器实现均匀光强分布的理论模型,并验证了Paturz等人的实验结果,为此种新型阵列器的研究提供了基础.     

高分辨紫外电子轰击互补金属氧化物半导体器件的实验研究

基于真空紫外光电阴极和背照式互补金属氧化物半导体(CMOS)图像传感器研制了紫外光响应的电子轰击CMOS(EBCMOS)器件,实现了EBCMOS器件在40 mlx光照度环境下的高分辨探测,电子图像灰度随电子能量的变化呈现出极好的线性关系.对器件成像分辨率测试的结果表明,在电场强度为5000 V/mm时,器件的空间分辨率可以达到25 lp/mm,与国际相关报道水平相当.研制的EBCMOS器件可直接在紫外弱光探测领域应用,如天文观察、高能物理、遥感测绘等,同时也可为下一步研制可见光和近红外敏感的EBCMOS器件提供参考.     

不同偏压下Zn1-xCdxSe-ZnSe超晶格室温电调制反射谱研究

首次研究了在室温和不同直流偏压下Zn_1-xCd_xSe-ZnSe超晶格结构的电调制反射谱(ER)的变化。当器件处于弱场范围时,随着电场的增加,ER谱的信号幅度增加,而线型不变;在强场区,随着电场的增加,ER谱的线型发生变化,激子跃迁能量红移,继续增加反向偏压出现来自于1c-2hh的禁戒跃迁,且其强度随反向偏压的增加迅速增加。不同偏压下组合超晶格结构的ER谱研究表明,势垒高度较低的超晶格结构中的激子较易受到电场的调制。     

产生纳米级暗中空光束的方法研究

用时域有限差分法，给出光纤头近场区电场强度模的空间分布.讨论了当光纤纤芯分别取不同尺寸时，对此空间光场强度的影响.要想得到较大范围的暗中空光束，必须增加光纤纤芯尺寸.并且，对光纤纤芯尺寸取一较大值和光纤中空区域尺寸取一较小值时的情况进行讨论，可得在光纤头附近可以出现与光纤中空区域尺寸大小相当的暗斑(10¹ nm量级).但是，暗中空光束中背景光较强.为此，将光纤的空心设计为金属. 发现此时中心暗斑的背景光明显减弱，在近场区域可获得较为理想的暗中空光束.如进一步缩小光纤中空区域尺寸，可以在光纤头附近获得暗斑更小甚至纳米量级的暗中空光束.为获得一种纳米量级的暗中空光束提供一种方法.     

Generation of an axial magnetic field from photon spin

In circularly polarized light the spins of the photons are aligned. When a short intense pulse of circularly polarized laser light is absorbed by a plasma, a torque is delivered initially to the electron species, resulting primarily in an opposing torque from an induced azimuthal electric field. This electric field, in general, has a curl and leads to the generation of an axial magnetic field. It also is the main means for transferring angular momentum to the ions. The time-dependent magnetic field has a magnitude proportional to the transverse gradient of the absorbed intensity but inversely proportional to the electron density, in contrast to earlier theories of the inverse Faraday effect.     

Calculation of the temperature and thermal expansion of a STM tip heated by a short laser pulse

A mathematical model for the calculation of the temperature field in a scanning tunneling microscope (STM) tip under laser illumination is developed. The duration of the laser pulse is a few nanoseconds or shorter. A Gaussian distribution of the laser light intensity in time and space is assumed. Two different mechanisms of tip heating are taken into account: 1. due to an enhanced electric field on the tip; 2. due to heating of the side surface of the tip by the focused spot of laser light. An average tip temperature is calculated using the heat conductivity equation. The enhanced electric field on the tip is calculated by the method of boundary integral equations. Received: 20 August 2002 / Revised version: 4 December 2002 / Published online: 19 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-2551/962-490, E-mail: sklein@fh-muenster.de     

Multiphoton intraband absorption of electromagnetic waves and stimulated scattering by optical phonons in the superlattice

Multiphoton intraminiband absorption of the electromagnetic wave and stimulated scattering by optical phonons in the semiconductor superlattice are considered. The absorption coefficient is found without using the quantum kinetic equation. The absorbed energy is plotted versus the electric field of the wave. It is found that, as the electric field grows, the absorbed energy reaches a maximum and then starts decreasing in an oscillatory manner. An explanation for such a run of the absorbed energy with electric field is given. It is shown that multiphoton absorption must be taken into account if the condition eEd ≥ ?ω is satisfied. Stimulated multiphoton scattering by optical phonons in superlattices is shown to produce harmonics of the scattered light at frequencies both higher and lower than those of the incident light. Scattering partial cross sections are found and plotted versus the incident wave intensity.     

Statistical properties in the chaotic regime of the Maxwell-Bloch equations

The statistical properties of the electric field solution of the Maxwell-Bloch equations describing a single mode, homogeneously broadened laser in the mean field limit are investigated in the strange attractor regime. The electric field distribution sis calculated and it is found that the low order intensity moments are somewhat higher than those for thermal-chaotic light whilst the higher order moments are substantially lower. The field and intensity correlation functions are also calculated and found to exhibit radically different behaviour. The results are interpreted in terms of iterative map which is dederived using multiple time-scale perturbation theory. It is shown that a simple random phasor model is compatible with the numerical data.     

双缺陷模一维光子晶体的双光子吸收增强研究

采用真空镀膜工艺制备了具有762 nm和800 nm双缺陷模的含两个CdS缺陷层的TiO2/SiO2一维光子晶体,运用抽运探测技术测量了其双光子吸收。对于两个缺陷模,双光子吸收均得到很大的增强,其中缺陷模为800nm时的双光子吸收系数307 cm/GW要大于缺陷模为762 nm时的116 cm/GW,分别为单层CdS薄膜的48倍和18倍。这种双光子吸收的增强是由于光局域化导致一维光子晶体缺陷层内的电场强度增大而形成的。通过传输矩阵法计算了一维光子晶体的内部场强,发现800 nm波长光入射时缺陷层内的电场强度要大于762 nm波长光入射时的电场强度值。     

Integrated optical electric field sensor based on a Bragg grating in lithium niobate

We demonstrate a new sensor concept for the measurement of oscillating electric fields that is based on Bragg gratings in LiNbO₃:Ti channel waveguides. This miniaturized sensor that works in a retroreflective scheme does not require metallic electrodes and can be directly immersed in an oscillating electric field. The electric field induces a shift of the Bragg wavelength of the reflection grating that is due to the electro-optic effect. The operating point of the sensor is chosen by adjusting the laser wavelength to the slope of the spectral reflectivity function of the grating. In this way the magnitude of an external electric field is measured precisely as the amplitude of modulated reflected light intensity by using a lock-in amplifier. The sensor principle is demonstrated by detecting low-frequency electric fields ranging from 50 V/cm to 5 kV/cm without any conducting parts of the sensor head. Furthermore, the ability of the sensor to determine the three-dimensional orientation of an external electric field by a single rotation along the waveguide direction is demonstrated. PACS 42.40.Eq; 42.82.-m; 42.82.Et